J Neurosurg 48:946-956, 1978
Studies of the third circulation Amipaque CT cisternography and ventriculography BURTON P. DRAYER, M.D., AND ARTHUR E. ROSENBAUM, M.D.
Department of Radiology, Division of Neuroradiology, University of Pittsburgh School of Medicine, Presbyterian-University Hospital, Pittsburgh, Pennsylvania u," The techniques of Amipaque (metrizamide) computerized tomography (CT) cisternography and Amipaque CT ventriculography are described. Normal, intermediate, delayed, and obstructive cerebrospinal fluid circulation patterns are readily demonstrated by evaluation ofventricular stasis of Amipaque on serial CT scans. Both the morphological and physiologicalcharacteristics of intracranial cysts are accurately defined and a diagnostic classificationis presented. The functional integrity of ventricular shunts can be appraised using the ventricular persistence of Amipaque as a primary criterion. Other applications of these modalities are described and their place in the neurodiagnostic armamentarium is discussed. KEY WORDS 9 computerized tomography cisternography 9 ventriculography 9 Amipaque (metrizamide) 9 CSF circulation cysts, central nervous system 9 ventricular shunt
INCE its early clinical applications ipnhy1964,6 radionuclide cisternograhas become the primary radiodiagnostic modality for the evaluation of cerebrospinal fluid (CSF) disorders. This technique has provided important and often diagnostic information in various clinical situations including communicating hydrocephalus, 15 ventricular shunt malfunction,12 cysts, 4 and CSF fistulas. 8 However, radionuclide cisternographic studies have certain limitations 16 which include poor morphological detail, a significant incidence of test failures, and the complicated handling of radioisotopic materials. Cranial computerized tomography (CT), T M although an anatomic technique, has proven useful in the evaluation of hydrocephalusH and extra-axial cysts? 8 Direct physiological information concerning the CSF circulation
S
946
in hydrocephalus has been monitored using small doses of Amipaque (metrizamide) administered via either the lateral ventricles or the lumbar subarachnoid spaces and serially imaged using CT. 7,13 This radiodiagnostic modality, Amipaque CT cisternography (CTC), can be used for the diagnosis of the various CSF circulation abnormalities,7's'13 which was previously restricted to the domain of radionuclide cisternography. For the first time Amipaque CTC provides the capacity for a single radiological examination to accurately and simultaneously assess both morphological and physiological information. Materials and Methods
Amipaque CTC studies were performed on 63 patients aged 8 months to 69 years. Individuals receiving neuroleptic drugs or with a
J. Neurosurg. / Volume 48 /June, 1978
Amipaque CT cisternography and ventriculography TABLE 1 CSF circulation patterns using Amipaque CTC and CTV* Circulation Pattern Type I: normal Type II: intermediate
Type III: intermediate Type IV: delayed Type V: obstructive**
Primary: Secondary: Periventricular Parasagittal V e n t r i c u l a r Slow SAS Stasist Ascent:~ ~ Absorptionw BlushlJ 0 + + ++ X )< X
0 0 + 0/+ --
0 0 0 0/+ 0/+
+ + ++ 0/+ 0
*CSF = cerebrospinal fluid; CTC = computerized tomography (CT) cisternography; CTV = CT ventriculography. tVentricular stasis of Amipaque: 0 = none at 24 hours; + = mild at 24 hours; -t-q- = moderate to severe at 24 hours; X X X = site of ventricular obstruction ascertained. ~Persistence of well defined Amipaque in basal subarachnodi cisterns at 12 hours: 0 = normal, poor definition; + = sharp definition; -- = none or minimal amount present. SAS --- subarachnoid spaces. w decreased absorption on 0.2 or 6 hour CT: 0 = none; + = present. [IParasagittal blush: + = best seen at 6 and 12 hours (normal); + + = best seen at 24 or 36 hours (delayed); 0 = never well seen. **Criteria using Amipaque CTV.
history of iodine allergy or seizure disorder were not studied. A baseline neurological examination was performed, followed by repeat evaluations 6 and 24 hours after Amipaque administration. The respiratory rate, heart rate, and temperature were also monitored. In adults, usually no premedication was needed. In children under the age of 12 years, intramuscular secobarbital and morphine sulphate were given 30 minutes before the procedure. General anesthesia was rarely necessary. With the patient lying p r o n e on a myelographic tilt table, a lumbar puncture was performed using a No. 22 spinal needle. Amipaque was then introduced (6.0 ml of 190 mg iodine per ml (I/ml) in adults, and 1.5 to 5.0 ml of 190 mg I / m l in children) with brief fluoroscopic monitoring to insure its subarachnoid administration. The needle was then removed, the patient turned supine, and the tilt table moved to a - 60 ~ head down (Trendelenberg) position for 1 minute. The table was returned to - 15 ~ Trendelenberg and the patient was then moved to a similarly inclined stretcher for transfer to the CT scanner. For the immediate CT, a right triangular upholstered pillow was used with the patient lying along its hypotenuse and the head always lower than the remainder of the body. Great care was taken in all transfers to assure that the head remained dependent, J. Neurosurg. / Volume 48 / June, 1978
thereby confining the hyperbaric contrast agent to the cranial region. Following the initial scans, the patient was kept in bed with the head elevated 45 ~ except during the times of serial scans (at 6, 12, 24, or 48 hours) which were performed with the patient lying flat. When a ventricular C S F diversionary shunt was in place, the Amipaque was introduced into the tubing or reservoir (Amipaque CT ventriculography, CTV) rather than by lumbar puncture. The remainder of the procedure was as described above except t h a t no positional maneuvers were necessary for adequate filling of the ventricles and subarachnoid spaces. Results
Cerebrospinal Fluid Circulation Patterns Table 1 summarizes the C S F circulation patterns with Amipaque C T C and CTV. The types are more fully described below. Type I: Normal. Thirty-eight patients were categorized as normal (Figs. 1 and 2). On the immediate (0.2 hour) CT, there was rapid filling of the basal subarachnoid cisterns and the Sylvian fissure. Even some cortical sulci were sharply delineated by the contrast material. The circulation of Amipaque toward the outflow arachnoid granulation system occurred via both the anterior and posterior subarachnoid spaces. The fourth ventricle can 947
B. P. Drayer and A. E. Rosenbaum
FIG. 1. Normal Amipaque computerized tomography cisternograms. Left: Pre-Amipaque, with enlarged lateral ventricles and subarachnoid spaces. Center."Six hours after Amipaque. Amipaque fills the lateral ventricles and cortical sulci. Right: Twenty-four hours after Amipaque. Amipaque has been totally cleared from the lateral ventricles. A very mild blushing of the cerebral regions adjacent to the subarachnoid spaces persists.
usually be completely filled with Amipaque using the described supine filling technique. The third and lateral ventricles contained Amipaque seen by CT in more than half of the cases studied. The brain regions immediately subjacent to the opacified subarachnoid spaces appeared free of Amipaque. By the 6-hour CT, the subarachnoid spaces were sharply defined. Mild persistence of Amipaque in the lateral ventricles was not unusual. A prominent staining now occurred in areas adjacent to the cerebral and cerebellar subarachnoid spaces. The deeper cerebral regions and the brain stem did not stain. On the 12-hour CT, visualization of the basal subarachnoid cisterns became less dis-
FIG. 2. Normal Amipaque computerized tomography cisternograms. Left: Before Amipaque administration, showing mildly dilated cortical sulci. Right: Twelve hours after Amipaque, blushing (B) is prominent in the parasagittal and lateral convexity regions. A few cortical sulci (S) remain well visualized. 948
tinct. Minimal or no Amipaque could be detected in the lateral ventricles. The parasagittal, lateral convexity, and cerebellar blushing remained prominent. The 24-hour CT showed almost total clearing of Amipaque from the subarachnoid spaces. The ventricles were free of contrast media. The symmetrical brain blushing was far less evident. Types I I and 111." Intermediate. Nine patients fell into the intermediate group (Fig. 3). The general circulation of Amipaque through the various subarachnoid spaces in its ascent to the arachnoid granulations was sometimes delayed, especially when the basal cisterns were capacious. This was evidenced by persistence of well defined contrast media in the basal subarachnoid cisterns for 12 hours or longer and by a delayed appearance of the maximal parasagittal blush. A mild amount of ventricular stasis of Amipaque at 24 hours was the cardinal feature of the intermediate patterns. No periventricular rim of decreased absorption was visualized in these cases. Type IV." Delayed Pattern. Ten patients showed a delayed pattern (Fig. 4). The most prominent feature of this circulation pattern was the moderate-to-severe ventricular stasis of Amipaque seen on the serial CT at 24 hours. Associated findings that were diagnostically useful, although inconstant, included a periventricular rim of decreased absorption and a diminished parasagittal blush. Radionuclide (16gy) cisternographic findings
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Arnipaque CT cisternography and ventriculography
FIG. 3. Intermediate Amipaque computerized tomography cisternograms. Left: Pre-Amipaque, showing enlarged lateral ventricles and subarachnoid spaces. Center:Twelve hours post-Amipaque, the lateral ventricles (v) contain Amipaque, making them isodense with the brain substance. Right: Twentyfour hours post-Amipaque, a small amount of Amipaque persists (stasis) in the lateral ventricles.
correlated with the Amipaque CTC results in the four patients who were examined by both techniques. Type V: Obstructive Pattern. Four patients exhibited obstruction (Fig. 5). When Amipaque was introduced via the ventricular diversionary shunt (Amipaque CTV), the presence of an obstructive phenomenon in the ventricular system or outflow tract was readily demonstrated by non-filling of the ventricular system or subarachnoid spaces distal to the obstruction. Sites of obstruction studied have included the foramina of Monro
(two cases) and Magendie and Luschka (two cases). Amipaque CTC, when done, confirmed the location of blockage. In one patient who was studied following surgical removal of an obstructing mass, free flow to Amipaque was restored.
Intracranial Cysts A morphological-physiological classification of central nervous system ( C N S ) cysts as defined by Amipaque C T C a n d / o r CTV emerged from this study (Table 2). A total of
FIG. 4. Delayed Amipaque computerized tomographic cisternograms. Left: At 0.2 hours postAmipaque, Amipaque opacities the dependent portions of the lateral ventricles (v). A periventricular rim of diminished absorption (arrowheads) is accentuated by the Amipaque tilling of the lateral ventricles. Center: Twenty-four hours post-Amipaque, there is prominent Amipaque stasis in the lateral ventricles (v), which is now evenly distributed throughout. Right: Forty-eight hours post-Amipaque, the ventricular stasis of Amipaque (v) persists even at this late time interval.
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B. P. Drayer and A. E. Rosenbaum TABLE 2 lntracranial cyst spectrum using Amipaque CTC and CTV*
Cyst Classification Subarachnoid capacious normal cisternt communicating EAC (immediate)t communicating EAC (delayed) noncommunicating EAC (such as epidermoid, neuroepithelial, arachnoid, poorly differentiated) Outlet Dandy-Walker cyst Ventrietdar porencephaly (comm) intra-axial cyst (noncommunicating)
Filling Following Subarachnoid Amipaque Administration (CTC) No. of ImmedCases iate Delayed 2 2 3
q+
None
+ +
2
+ +
Immediate Delayed + +
2
1 3
Filling Following Ventricular Amipaque Administration (CTV)
+
None
+ +
+ +
+
*CTC = computerized tomography (CT) cisternography; CTV = CT ventriculography; EAC = extraaxial cyst. revert with a combination of Amipaque CTC, pneumoencephalography, and angiography, it is often extremely difficult to separate the normal enlarged cistern (such as in cisterna magna) from the freely communicating extra-axial cyst.
15 p a t i e n t s were studied, with a d i a g n o s i s o f CNS cyst or enlarged cisterna magna. Pneumoencephalography and/or angiogr a p h y were p e r f o r m e d in all 15 i n d i v i d u a l s a n d e i g h t o f these h a d s u r g i c a l i n t e r v e n t i o n .
Subarachnoid Cysts. A m i p a q u e fills either a communicating extra-axial cyst or a c a p a c i o u s , n o r m a l c i s t e r n (for instance, an enlarged cisterna magna) immediately. The d i s t i n c t i o n o f t h e s e t w o entities (Fig. 6) was
FIG. 5. Undifferentiated cyst and obstructive hydrocephalus. Left: Pre-Amipaque, markedly dilated lateral ventricles can be seen with a large cystic structure either adjacent to or communicating with the ventricle. Center: At 0.2 hours post-Amipaque, Amipaque fills the lateral ventricles but not the cystic structure, that is, the low-absorption area is not in communication with the lateral ventricles. The third and fourth ventricles and basal subarachnoid cisterns did not opacify with Amipaque, denoting an obstructive hydrocephalus. Right: Six hours post-Amipaque. No filling of the cyst occurred on delayed scans. At surgery, an undifferentiated cyst was removed which was not in communication with the lateral ventricles, and compressed but did not infiltrate the brain substance. 950
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Amipaque CT cisternography and ventriculography
FIG. 6. Retrocerebellar (communicating) extra-axial cyst versus enlarged cisterna Routine computerized magna. Upper: tomography (CT) scan. Large area of diminished attenuation coefficient posterior to a small cerebellum. The fourth ventricle (arrow) and brain stem (B) are compressed from behind. Center." Amipaque CT cisternograms at 0.2 hours. Amipaque immediately fills the large retrocerebellar cystic region. Lower Right." Pneumoencephalogram, anteroposterior, brow down view. Oxygen fills the large retrocerebellar area noted on computerized tomography. On lateral views the fourth ventricle was displaced anteriorly. Vertebral angiography displayed the anteriorly displaced vermian and hemispheric branches of the posterior inferior cerebellar artery as well as the small cerebellum. Therefore, a definitive distinction between cisterna magna and cyst cannot be made, although a communicating cyst is most likely.
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951
B. P. Drayer and A. E. Rosenbaum cyst from adjacent brain, thus definitively establishing its extra-axial nature. Outlet Foraminal (Fourth Ventricle) Cysts. Amipaque CTV showed ready filling of the large region of diminished absorption in the posterior fossa (Fig. 8). Moreover, definitive proof of outlet foramina obstruction (DandyWalker cyst) was obtained by the absence of Amipaque in the basal subarachnoid cisterns. Ventricular Cysts. The diagnosis of porencephaly was established by the ready opacification of a lateral ventricular outpouching with water-soluble contrast media. With both extra-axial and intra-axial brain cysts, no filling of the cystic region occurred even with adequate Amipaque in the ventricles and positional manipulations.
Ventricular Shunt Function
FIG. 7. Delayed communicating extra-axial cyst. Upper." Immediate post-Amipaque scans. Amipaque opacities the basal subarachnoid cisterns, but does not fill the cystic region. Lower Left." Six hours post-Amipaque. A small amount of Amipaque penetrates the cystic region. Lower Right: Twelve hours post-Amipaque. Amipaque has almost totally cleared from the cyst.
difficult with Amipaque CT techniques as with pneumoencephalography and angiography. The differentiation was often dependent on associated findings (such as, hydrocephalus and abnormal CSF circulation favoring cyst) which were best delineated with Amipaque CTC. When no communication was present between the Amipaque in the subarachnoid space and the cyst on the immediate (0.2 to 1.0 hour) CT scan, diffusion-penetrance of Amipaque into the cyst (Fig. 7) sometimes occurred over several hours (delayed communicating extra-axial cyst). In some individuals, no Amipaque entered the cystic area (Fig. 5) on either the immediate or delayed CT scans (noncommunicating extraaxial cyst). A cleavage plane of subarachnoid Amipaque often separates an intracranial 952
Eight individuals were studied by serial CT following the administration of Amipaque into a ventricular shunt system (Amipaque CT ventriculography). With "normal" shunt function (four patients), the immediate CT showed Amipaque filling the lateral ventricles. When ventricular obstruction was not present, Amipaque also opacified the basal subarachnoid cisterns. If a body scanner was used, the contrast media could also be promptly visualized at the peritoneal end of the shunt tubing. Within 12 hours, the lateral ventricles were fully cleared of Amipaque. Shunt "malfunction" (four patients) was readily distinguished by the persistence of Amipaque in the lateral ventricles at 24 hours (Fig. 9).
Cerebrospinal Fluid Fistulas Cerebrospinal fluid rhinorrhea (two patients) was readily defined following lumbar injection of Amipaque by the layering of contrast in the appropriate nasal passage with the patient prone. The site of the fistula was also delineated using an EMI 5000 body scanner (Fig. 10).
Adverse Reactions Among the 39 adults and 24 children, headache (20 adults and four children), and nausea with vomiting (18 adults and six children) were the most common side effects. Subtle perceptual alterations (four adults and one child) were noted only if the patient and
J. Neurosurg. / Volume 48 / June, 1978
Amipaque CT cisternography and ventriculography
FIG. 8. Dandy-Walker cyst demonstrated on Amipaque computerized tomography cistograms. A: A large cystic region in the posterior fossa immediately fills with Amipaque (1.5 ml of 190 mg I/ml) injected through the ventriculoperitoneal shunt reservoir. The anterior pointing of this abnormality excludes an enlarged cisterna magna. B: The cystically dilated fourth ventricle is now clearly seen. On this scan and on serial scans over 24 hours, the basal subarachnoid cisterns never opacified, affirming fourth ventricular outlet obstruction. C, D, and E: The superior extension of the cyst has a maximum height of 32 mm (overlapping slice determination, confirmed radiographically). The straightened medial margins of the lateral ventricles suggest concomitant agenesis of the corpus callosum. F. Specific attenuation coefficient (+ 35 Hounsfield units) of B better defines the cyst and its relationships to the inner table posteriorly.
family were questioned in detail. Adverse reactions were usually delayed in onset and in most instances persisted for less than 24 hours. N o side effects were observed in 15 adults and 15 children.
Discussion A m i p a q u e is an investigational, non-ionic, intrathecal contrast agent of lowered toxicity due to its decreased osmolality. 1 The relative safety of this water-soluble glucosamide of m e t r i z o i c acid has been evidenced in laboratory and h u m a n experience with radiJ. Neurosurg. / Volume 48 / June, 1978
culomyelography, cisternography, and ventriculography. ~7 Since large volumes and high concentrations of this contrast m e d i u m seem to correlate with an increased incidence of adverse reactions, TM reduced dosages are obviously preferred and are p e r m i t t e d by the high resolution of C T imaging. However, even using this method with lowered doses, adverse reactions (usually mild to m o d e r a t e in intensity and lasting less than 24 hours) occurred in 53% of the individuals studied. These side effects were delayed in onset and correlated closely with the m a x i m a l Amipaque blush. 7,8 953
B. P. Drayer and A. E. Rosenbaum
FIG. 9. Ventricular shunt malfunction. Left: Pre-Amipaque, showing dilated lateral ventricles and shunt artifact. Center." Twelve hours after Amipaque, prominent opacification of the lateral ventricles with Amipaque can be seen. Right: Twenty-four hours post-Amipaque, ventricular stasis of Amipaque continues, thus confirming the malfunction of the ventriculoperitoneal shunt.
FIG. 10. Cerebrospinal fluid (CSF) leak, visualized by supine computerized tomography. Left." Amipaque, introduced by lumbar puncture, is seen in the basal subarachnoid spaces defining the midbrain (M). Air was incidentally introduced and fills the temporal horn of the lateral ventricle (T). Note the Amipaque (arrowhead) layered in the posterior portion of the ethmoid sinus denoting a CSF fistula (confirmed at surgery). Right: Amipaque (arrowhead) is visualized in the pharynx (P) confirming CSF leakage. The patient described tasting iodine. 954
J. Neurosurg. / Volume 48 / June, 1978
Amipaque CT cisternography and ventriculography Following either the intraventricular or lumbar intrathecal introduction of Amipaque, the contrast medium progresses in a unidirectional fashion toward the intracranial arachnoid granulations in a manner paralleling that described for subarachnoid injected radionuclides), is Amipaque therefore appears to accurately reflect the circulation characteristics of CSF. Amipaque CT suggests that the CSF follows both an anterior and posterior route (rather than predominantly anterior ~) in its ascent to the convexity and parasagittal regions. The most important criterion of "abnormal" CSF circulation is ventricular stasis, whether using Amipaque C T C / C T V or radionuclide cisternography/ventriculography. Ancillary signs are often helpful using either technique, that is, parasagittal activity with radionuclide or parasagittal blushing with Amipaque. Computerized tomography enhanced with water-soluble contrast material affords the advantage of improved morphological detail which enables the distinction of subtleties such as periventricular edema. Elaborate precautions must be taken in the handling of radioactive substances as opposed to the simple mixing of lyophilized Amipaque with its diluent. The only disadvantage of the Amipaque CT studies was the incidence of adverse reactions, which are not severe enough to limit the usefulness of the technique. With differing premedication regimens before the use of Amipaque and with the development of even lower toxicity water-soluble contrast agents, this disadvantage should be readily overcome. Amipaque CTV seems a simple and reliable method to evaluate the functioning of a ventricular shunt system. In the clinical situation in which a shunt malfunction is suspected and previous CT scans are not available or the comparison CT findings are not definitive, ventricular persistence of Amipaque and the absence of abdominal contrast media (if the shunt is totally obstructed distally) confirm the presence of malfunction. A combination of Amipaque CTC 9 and/or Amipaque CTV 1~has proven the most useful diagnostic approach to intracranial cysts. Angiography provides mainly anatomical information. Pneumoencephalography is of limited physiological usefulness and carries a high morbidity. Routine CT again provides basically morphological data, although the J. Neurosurg. / Volume 48 / June, 1978
visualization of hydrocephalus allows mechanistic suppositions. Amipaque CTC or CTV present both precise morphological (such as extra-axial location of cyst) and functional (such as Dandy-Walker versus posterior fossa extra-axial cyst; delayed communication of cyst) information in a single, rapidly performed study. In addition, the circulation of the CSF, the mechanism of the hydrocephalus, and the functioning of a therapeutic shunt may also be defined by this single test. It appears that the use ofpneumoencephalography, angiography, and radionuclide studies may be obviated in the diagnostic evaluation of most brain cysts. Acknowledgments
We wish to acknowledge Jeane Dobrinski for her secretarial assistance, the Departments of Neurology and Neurosurgery for their excellent patient care, and the Neuroradiology Staff (Z. L. Deeb, W. O. Bank, E. R. Heinz, P. B. Markarian, and J. A. Horton) for their assistance and encouragement. References
1. AIm6n T: Contrast agent design. Some aspects of the synthesis of water soluble contrast agents of low osmolality. J Theoret Biol 24: 216-226, 1969 2. Ambrose J" Computerized transverse axial scanning (tomography): Part 2. Clinical application. Br J Radiol 46:1023-1047, 1973 3. Ashburn WL, Harbert JC, Briner WH, et al: Cerebrospinal fluid rhinorrhea studied with the gamma scintillation camera. J Nucl Med 9:523-529, 1968 4. Conway J J, Yarzagaray L, Welch D: Radionuclide evaluation of the Dandy-Walker malformation and congenital arachnoid cyst of the posterior fossa. Am J Roentgenoi Radium Ther Nucl Med 112:306-314, 1971 5. Di Chiro G: Movement of the cerebrospinal fluid in human beings. Nature 204:290-291, 1964
6. Di Chiro G, Reames PM, Mathews WB Jr: RISA-ventriculography and RISA-cisternography. Neurology 14:185-191, 1964 7. Drayer BP, Rosenbaum AE: Amipaque brain penetrance. Its correlation with adverse reactions and value radiodiagnostically. Acta Radiol (Supp!) (In press) 8. Drayer BP, Rosenbaum AE, Higman HB: Cerebrospinal fluid imaging using serial metrizamide CT cisternography. Neuroradiology 13:7-17, 1977 955
B. P. Drayer and A. E. Rosenbaum 9. Drayer BP, Rosenbaum AE, Maroon JC, et al: Posterior foSsa extraaxial cyst: Diagnosis with metrizamide CT cisternography. Am J Roentgenol 128:431-436, 1977 I0. Drayer BP, Rosenbaum AE, Strand RD, et al: Amipaque CT ventriculography. Diagnostic applications. Paper presented at the 15th Annual Meeting of the American Society of Neuroradiology, Hamilton, Bermuda, March, 1977 11. Gado MH, Coleman RE, Lee KS, et al: Correlation between computerized transaxial tomography and radionuclide cisternography in dementia. Neurology 26:555-560, 1976 12. Gilday DL, Kellam J: ~11In-DTPA evaluation of CSF diversionary shunts in children. J Nucl Med 14:920-923, 1973 13. Greitz T, Hindmarsh T: Computer assisted tomography of intracranial CSF circulation using a water-soluble contrast medium. Acta Radioi (Diagn) 15:497-507, 1974 14. Hounsfield GN: Computerized transverse axial scanning (tomography): Part 1. Description of system. Br J Radiol 46:1016-1022, 1973 15. James AE Jr, New PFJ, Heinz ER, et al: A cisternographic classification of hydrocepha-
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16.
17. 18. 19.
lus. Am J Roentgenol Radium Ther Nucl Med 115:39-49, 1972 McAfee IG, Subramanian G: Radioactive agents for imaging, in Freeman LM, Johnson PM (eds): Clinical Scintillation Imaging, ed 2. New York: Grune and Stratton, 1975, pp 13-114 Metrizamide: Metrizamide. A non-ionic water-soluble contrast medium. Acta Radiol (Suppl) 335:1-390, 1973 Naidich TP, Epstein F, Lin JP, et al: Evaluation of pediatric hydrocephalus by computed tomography. Radiology 119:337-353, 1976 Wylie IG, Afshar F, Koeze TH: Results of the use of a new water-soluble contrast medium (metrizamide) in the posterior fossa of the baboon. Br J Radiol 48:1007-1012, 1975
Address reprint requests to: Burton P. Drayer, M.D., Department of Radiology, University of Pittsburgh School of Medicine, Presbyterian-University Hospital, 230 Lothrop Street, Pittsburgh, Pennsylvania 15261.
J. Neurosurg. / Volume 48 /June, 1978
Studies of the third circulation Amipaque CT cisternography and ventriculography BURTON P. DRAYER, M.D., AND ARTHUR E. ROSENBAUM, M.D.
Department of Radiology, Division of Neuroradiology, University of Pittsburgh School of Medicine, Presbyterian-University Hospital, Pittsburgh, Pennsylvania u," The techniques of Amipaque (metrizamide) computerized tomography (CT) cisternography and Amipaque CT ventriculography are described. Normal, intermediate, delayed, and obstructive cerebrospinal fluid circulation patterns are readily demonstrated by evaluation ofventricular stasis of Amipaque on serial CT scans. Both the morphological and physiologicalcharacteristics of intracranial cysts are accurately defined and a diagnostic classificationis presented. The functional integrity of ventricular shunts can be appraised using the ventricular persistence of Amipaque as a primary criterion. Other applications of these modalities are described and their place in the neurodiagnostic armamentarium is discussed. KEY WORDS 9 computerized tomography cisternography 9 ventriculography 9 Amipaque (metrizamide) 9 CSF circulation cysts, central nervous system 9 ventricular shunt
INCE its early clinical applications ipnhy1964,6 radionuclide cisternograhas become the primary radiodiagnostic modality for the evaluation of cerebrospinal fluid (CSF) disorders. This technique has provided important and often diagnostic information in various clinical situations including communicating hydrocephalus, 15 ventricular shunt malfunction,12 cysts, 4 and CSF fistulas. 8 However, radionuclide cisternographic studies have certain limitations 16 which include poor morphological detail, a significant incidence of test failures, and the complicated handling of radioisotopic materials. Cranial computerized tomography (CT), T M although an anatomic technique, has proven useful in the evaluation of hydrocephalusH and extra-axial cysts? 8 Direct physiological information concerning the CSF circulation
S
946
in hydrocephalus has been monitored using small doses of Amipaque (metrizamide) administered via either the lateral ventricles or the lumbar subarachnoid spaces and serially imaged using CT. 7,13 This radiodiagnostic modality, Amipaque CT cisternography (CTC), can be used for the diagnosis of the various CSF circulation abnormalities,7's'13 which was previously restricted to the domain of radionuclide cisternography. For the first time Amipaque CTC provides the capacity for a single radiological examination to accurately and simultaneously assess both morphological and physiological information. Materials and Methods
Amipaque CTC studies were performed on 63 patients aged 8 months to 69 years. Individuals receiving neuroleptic drugs or with a
J. Neurosurg. / Volume 48 /June, 1978
Amipaque CT cisternography and ventriculography TABLE 1 CSF circulation patterns using Amipaque CTC and CTV* Circulation Pattern Type I: normal Type II: intermediate
Type III: intermediate Type IV: delayed Type V: obstructive**
Primary: Secondary: Periventricular Parasagittal V e n t r i c u l a r Slow SAS Stasist Ascent:~ ~ Absorptionw BlushlJ 0 + + ++ X )< X
0 0 + 0/+ --
0 0 0 0/+ 0/+
+ + ++ 0/+ 0
*CSF = cerebrospinal fluid; CTC = computerized tomography (CT) cisternography; CTV = CT ventriculography. tVentricular stasis of Amipaque: 0 = none at 24 hours; + = mild at 24 hours; -t-q- = moderate to severe at 24 hours; X X X = site of ventricular obstruction ascertained. ~Persistence of well defined Amipaque in basal subarachnodi cisterns at 12 hours: 0 = normal, poor definition; + = sharp definition; -- = none or minimal amount present. SAS --- subarachnoid spaces. w decreased absorption on 0.2 or 6 hour CT: 0 = none; + = present. [IParasagittal blush: + = best seen at 6 and 12 hours (normal); + + = best seen at 24 or 36 hours (delayed); 0 = never well seen. **Criteria using Amipaque CTV.
history of iodine allergy or seizure disorder were not studied. A baseline neurological examination was performed, followed by repeat evaluations 6 and 24 hours after Amipaque administration. The respiratory rate, heart rate, and temperature were also monitored. In adults, usually no premedication was needed. In children under the age of 12 years, intramuscular secobarbital and morphine sulphate were given 30 minutes before the procedure. General anesthesia was rarely necessary. With the patient lying p r o n e on a myelographic tilt table, a lumbar puncture was performed using a No. 22 spinal needle. Amipaque was then introduced (6.0 ml of 190 mg iodine per ml (I/ml) in adults, and 1.5 to 5.0 ml of 190 mg I / m l in children) with brief fluoroscopic monitoring to insure its subarachnoid administration. The needle was then removed, the patient turned supine, and the tilt table moved to a - 60 ~ head down (Trendelenberg) position for 1 minute. The table was returned to - 15 ~ Trendelenberg and the patient was then moved to a similarly inclined stretcher for transfer to the CT scanner. For the immediate CT, a right triangular upholstered pillow was used with the patient lying along its hypotenuse and the head always lower than the remainder of the body. Great care was taken in all transfers to assure that the head remained dependent, J. Neurosurg. / Volume 48 / June, 1978
thereby confining the hyperbaric contrast agent to the cranial region. Following the initial scans, the patient was kept in bed with the head elevated 45 ~ except during the times of serial scans (at 6, 12, 24, or 48 hours) which were performed with the patient lying flat. When a ventricular C S F diversionary shunt was in place, the Amipaque was introduced into the tubing or reservoir (Amipaque CT ventriculography, CTV) rather than by lumbar puncture. The remainder of the procedure was as described above except t h a t no positional maneuvers were necessary for adequate filling of the ventricles and subarachnoid spaces. Results
Cerebrospinal Fluid Circulation Patterns Table 1 summarizes the C S F circulation patterns with Amipaque C T C and CTV. The types are more fully described below. Type I: Normal. Thirty-eight patients were categorized as normal (Figs. 1 and 2). On the immediate (0.2 hour) CT, there was rapid filling of the basal subarachnoid cisterns and the Sylvian fissure. Even some cortical sulci were sharply delineated by the contrast material. The circulation of Amipaque toward the outflow arachnoid granulation system occurred via both the anterior and posterior subarachnoid spaces. The fourth ventricle can 947
B. P. Drayer and A. E. Rosenbaum
FIG. 1. Normal Amipaque computerized tomography cisternograms. Left: Pre-Amipaque, with enlarged lateral ventricles and subarachnoid spaces. Center."Six hours after Amipaque. Amipaque fills the lateral ventricles and cortical sulci. Right: Twenty-four hours after Amipaque. Amipaque has been totally cleared from the lateral ventricles. A very mild blushing of the cerebral regions adjacent to the subarachnoid spaces persists.
usually be completely filled with Amipaque using the described supine filling technique. The third and lateral ventricles contained Amipaque seen by CT in more than half of the cases studied. The brain regions immediately subjacent to the opacified subarachnoid spaces appeared free of Amipaque. By the 6-hour CT, the subarachnoid spaces were sharply defined. Mild persistence of Amipaque in the lateral ventricles was not unusual. A prominent staining now occurred in areas adjacent to the cerebral and cerebellar subarachnoid spaces. The deeper cerebral regions and the brain stem did not stain. On the 12-hour CT, visualization of the basal subarachnoid cisterns became less dis-
FIG. 2. Normal Amipaque computerized tomography cisternograms. Left: Before Amipaque administration, showing mildly dilated cortical sulci. Right: Twelve hours after Amipaque, blushing (B) is prominent in the parasagittal and lateral convexity regions. A few cortical sulci (S) remain well visualized. 948
tinct. Minimal or no Amipaque could be detected in the lateral ventricles. The parasagittal, lateral convexity, and cerebellar blushing remained prominent. The 24-hour CT showed almost total clearing of Amipaque from the subarachnoid spaces. The ventricles were free of contrast media. The symmetrical brain blushing was far less evident. Types I I and 111." Intermediate. Nine patients fell into the intermediate group (Fig. 3). The general circulation of Amipaque through the various subarachnoid spaces in its ascent to the arachnoid granulations was sometimes delayed, especially when the basal cisterns were capacious. This was evidenced by persistence of well defined contrast media in the basal subarachnoid cisterns for 12 hours or longer and by a delayed appearance of the maximal parasagittal blush. A mild amount of ventricular stasis of Amipaque at 24 hours was the cardinal feature of the intermediate patterns. No periventricular rim of decreased absorption was visualized in these cases. Type IV." Delayed Pattern. Ten patients showed a delayed pattern (Fig. 4). The most prominent feature of this circulation pattern was the moderate-to-severe ventricular stasis of Amipaque seen on the serial CT at 24 hours. Associated findings that were diagnostically useful, although inconstant, included a periventricular rim of decreased absorption and a diminished parasagittal blush. Radionuclide (16gy) cisternographic findings
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Arnipaque CT cisternography and ventriculography
FIG. 3. Intermediate Amipaque computerized tomography cisternograms. Left: Pre-Amipaque, showing enlarged lateral ventricles and subarachnoid spaces. Center:Twelve hours post-Amipaque, the lateral ventricles (v) contain Amipaque, making them isodense with the brain substance. Right: Twentyfour hours post-Amipaque, a small amount of Amipaque persists (stasis) in the lateral ventricles.
correlated with the Amipaque CTC results in the four patients who were examined by both techniques. Type V: Obstructive Pattern. Four patients exhibited obstruction (Fig. 5). When Amipaque was introduced via the ventricular diversionary shunt (Amipaque CTV), the presence of an obstructive phenomenon in the ventricular system or outflow tract was readily demonstrated by non-filling of the ventricular system or subarachnoid spaces distal to the obstruction. Sites of obstruction studied have included the foramina of Monro
(two cases) and Magendie and Luschka (two cases). Amipaque CTC, when done, confirmed the location of blockage. In one patient who was studied following surgical removal of an obstructing mass, free flow to Amipaque was restored.
Intracranial Cysts A morphological-physiological classification of central nervous system ( C N S ) cysts as defined by Amipaque C T C a n d / o r CTV emerged from this study (Table 2). A total of
FIG. 4. Delayed Amipaque computerized tomographic cisternograms. Left: At 0.2 hours postAmipaque, Amipaque opacities the dependent portions of the lateral ventricles (v). A periventricular rim of diminished absorption (arrowheads) is accentuated by the Amipaque tilling of the lateral ventricles. Center: Twenty-four hours post-Amipaque, there is prominent Amipaque stasis in the lateral ventricles (v), which is now evenly distributed throughout. Right: Forty-eight hours post-Amipaque, the ventricular stasis of Amipaque (v) persists even at this late time interval.
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B. P. Drayer and A. E. Rosenbaum TABLE 2 lntracranial cyst spectrum using Amipaque CTC and CTV*
Cyst Classification Subarachnoid capacious normal cisternt communicating EAC (immediate)t communicating EAC (delayed) noncommunicating EAC (such as epidermoid, neuroepithelial, arachnoid, poorly differentiated) Outlet Dandy-Walker cyst Ventrietdar porencephaly (comm) intra-axial cyst (noncommunicating)
Filling Following Subarachnoid Amipaque Administration (CTC) No. of ImmedCases iate Delayed 2 2 3
q+
None
+ +
2
+ +
Immediate Delayed + +
2
1 3
Filling Following Ventricular Amipaque Administration (CTV)
+
None
+ +
+ +
+
*CTC = computerized tomography (CT) cisternography; CTV = CT ventriculography; EAC = extraaxial cyst. revert with a combination of Amipaque CTC, pneumoencephalography, and angiography, it is often extremely difficult to separate the normal enlarged cistern (such as in cisterna magna) from the freely communicating extra-axial cyst.
15 p a t i e n t s were studied, with a d i a g n o s i s o f CNS cyst or enlarged cisterna magna. Pneumoencephalography and/or angiogr a p h y were p e r f o r m e d in all 15 i n d i v i d u a l s a n d e i g h t o f these h a d s u r g i c a l i n t e r v e n t i o n .
Subarachnoid Cysts. A m i p a q u e fills either a communicating extra-axial cyst or a c a p a c i o u s , n o r m a l c i s t e r n (for instance, an enlarged cisterna magna) immediately. The d i s t i n c t i o n o f t h e s e t w o entities (Fig. 6) was
FIG. 5. Undifferentiated cyst and obstructive hydrocephalus. Left: Pre-Amipaque, markedly dilated lateral ventricles can be seen with a large cystic structure either adjacent to or communicating with the ventricle. Center: At 0.2 hours post-Amipaque, Amipaque fills the lateral ventricles but not the cystic structure, that is, the low-absorption area is not in communication with the lateral ventricles. The third and fourth ventricles and basal subarachnoid cisterns did not opacify with Amipaque, denoting an obstructive hydrocephalus. Right: Six hours post-Amipaque. No filling of the cyst occurred on delayed scans. At surgery, an undifferentiated cyst was removed which was not in communication with the lateral ventricles, and compressed but did not infiltrate the brain substance. 950
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Amipaque CT cisternography and ventriculography
FIG. 6. Retrocerebellar (communicating) extra-axial cyst versus enlarged cisterna Routine computerized magna. Upper: tomography (CT) scan. Large area of diminished attenuation coefficient posterior to a small cerebellum. The fourth ventricle (arrow) and brain stem (B) are compressed from behind. Center." Amipaque CT cisternograms at 0.2 hours. Amipaque immediately fills the large retrocerebellar cystic region. Lower Right." Pneumoencephalogram, anteroposterior, brow down view. Oxygen fills the large retrocerebellar area noted on computerized tomography. On lateral views the fourth ventricle was displaced anteriorly. Vertebral angiography displayed the anteriorly displaced vermian and hemispheric branches of the posterior inferior cerebellar artery as well as the small cerebellum. Therefore, a definitive distinction between cisterna magna and cyst cannot be made, although a communicating cyst is most likely.
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B. P. Drayer and A. E. Rosenbaum cyst from adjacent brain, thus definitively establishing its extra-axial nature. Outlet Foraminal (Fourth Ventricle) Cysts. Amipaque CTV showed ready filling of the large region of diminished absorption in the posterior fossa (Fig. 8). Moreover, definitive proof of outlet foramina obstruction (DandyWalker cyst) was obtained by the absence of Amipaque in the basal subarachnoid cisterns. Ventricular Cysts. The diagnosis of porencephaly was established by the ready opacification of a lateral ventricular outpouching with water-soluble contrast media. With both extra-axial and intra-axial brain cysts, no filling of the cystic region occurred even with adequate Amipaque in the ventricles and positional manipulations.
Ventricular Shunt Function
FIG. 7. Delayed communicating extra-axial cyst. Upper." Immediate post-Amipaque scans. Amipaque opacities the basal subarachnoid cisterns, but does not fill the cystic region. Lower Left." Six hours post-Amipaque. A small amount of Amipaque penetrates the cystic region. Lower Right: Twelve hours post-Amipaque. Amipaque has almost totally cleared from the cyst.
difficult with Amipaque CT techniques as with pneumoencephalography and angiography. The differentiation was often dependent on associated findings (such as, hydrocephalus and abnormal CSF circulation favoring cyst) which were best delineated with Amipaque CTC. When no communication was present between the Amipaque in the subarachnoid space and the cyst on the immediate (0.2 to 1.0 hour) CT scan, diffusion-penetrance of Amipaque into the cyst (Fig. 7) sometimes occurred over several hours (delayed communicating extra-axial cyst). In some individuals, no Amipaque entered the cystic area (Fig. 5) on either the immediate or delayed CT scans (noncommunicating extraaxial cyst). A cleavage plane of subarachnoid Amipaque often separates an intracranial 952
Eight individuals were studied by serial CT following the administration of Amipaque into a ventricular shunt system (Amipaque CT ventriculography). With "normal" shunt function (four patients), the immediate CT showed Amipaque filling the lateral ventricles. When ventricular obstruction was not present, Amipaque also opacified the basal subarachnoid cisterns. If a body scanner was used, the contrast media could also be promptly visualized at the peritoneal end of the shunt tubing. Within 12 hours, the lateral ventricles were fully cleared of Amipaque. Shunt "malfunction" (four patients) was readily distinguished by the persistence of Amipaque in the lateral ventricles at 24 hours (Fig. 9).
Cerebrospinal Fluid Fistulas Cerebrospinal fluid rhinorrhea (two patients) was readily defined following lumbar injection of Amipaque by the layering of contrast in the appropriate nasal passage with the patient prone. The site of the fistula was also delineated using an EMI 5000 body scanner (Fig. 10).
Adverse Reactions Among the 39 adults and 24 children, headache (20 adults and four children), and nausea with vomiting (18 adults and six children) were the most common side effects. Subtle perceptual alterations (four adults and one child) were noted only if the patient and
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Amipaque CT cisternography and ventriculography
FIG. 8. Dandy-Walker cyst demonstrated on Amipaque computerized tomography cistograms. A: A large cystic region in the posterior fossa immediately fills with Amipaque (1.5 ml of 190 mg I/ml) injected through the ventriculoperitoneal shunt reservoir. The anterior pointing of this abnormality excludes an enlarged cisterna magna. B: The cystically dilated fourth ventricle is now clearly seen. On this scan and on serial scans over 24 hours, the basal subarachnoid cisterns never opacified, affirming fourth ventricular outlet obstruction. C, D, and E: The superior extension of the cyst has a maximum height of 32 mm (overlapping slice determination, confirmed radiographically). The straightened medial margins of the lateral ventricles suggest concomitant agenesis of the corpus callosum. F. Specific attenuation coefficient (+ 35 Hounsfield units) of B better defines the cyst and its relationships to the inner table posteriorly.
family were questioned in detail. Adverse reactions were usually delayed in onset and in most instances persisted for less than 24 hours. N o side effects were observed in 15 adults and 15 children.
Discussion A m i p a q u e is an investigational, non-ionic, intrathecal contrast agent of lowered toxicity due to its decreased osmolality. 1 The relative safety of this water-soluble glucosamide of m e t r i z o i c acid has been evidenced in laboratory and h u m a n experience with radiJ. Neurosurg. / Volume 48 / June, 1978
culomyelography, cisternography, and ventriculography. ~7 Since large volumes and high concentrations of this contrast m e d i u m seem to correlate with an increased incidence of adverse reactions, TM reduced dosages are obviously preferred and are p e r m i t t e d by the high resolution of C T imaging. However, even using this method with lowered doses, adverse reactions (usually mild to m o d e r a t e in intensity and lasting less than 24 hours) occurred in 53% of the individuals studied. These side effects were delayed in onset and correlated closely with the m a x i m a l Amipaque blush. 7,8 953
B. P. Drayer and A. E. Rosenbaum
FIG. 9. Ventricular shunt malfunction. Left: Pre-Amipaque, showing dilated lateral ventricles and shunt artifact. Center." Twelve hours after Amipaque, prominent opacification of the lateral ventricles with Amipaque can be seen. Right: Twenty-four hours post-Amipaque, ventricular stasis of Amipaque continues, thus confirming the malfunction of the ventriculoperitoneal shunt.
FIG. 10. Cerebrospinal fluid (CSF) leak, visualized by supine computerized tomography. Left." Amipaque, introduced by lumbar puncture, is seen in the basal subarachnoid spaces defining the midbrain (M). Air was incidentally introduced and fills the temporal horn of the lateral ventricle (T). Note the Amipaque (arrowhead) layered in the posterior portion of the ethmoid sinus denoting a CSF fistula (confirmed at surgery). Right: Amipaque (arrowhead) is visualized in the pharynx (P) confirming CSF leakage. The patient described tasting iodine. 954
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Amipaque CT cisternography and ventriculography Following either the intraventricular or lumbar intrathecal introduction of Amipaque, the contrast medium progresses in a unidirectional fashion toward the intracranial arachnoid granulations in a manner paralleling that described for subarachnoid injected radionuclides), is Amipaque therefore appears to accurately reflect the circulation characteristics of CSF. Amipaque CT suggests that the CSF follows both an anterior and posterior route (rather than predominantly anterior ~) in its ascent to the convexity and parasagittal regions. The most important criterion of "abnormal" CSF circulation is ventricular stasis, whether using Amipaque C T C / C T V or radionuclide cisternography/ventriculography. Ancillary signs are often helpful using either technique, that is, parasagittal activity with radionuclide or parasagittal blushing with Amipaque. Computerized tomography enhanced with water-soluble contrast material affords the advantage of improved morphological detail which enables the distinction of subtleties such as periventricular edema. Elaborate precautions must be taken in the handling of radioactive substances as opposed to the simple mixing of lyophilized Amipaque with its diluent. The only disadvantage of the Amipaque CT studies was the incidence of adverse reactions, which are not severe enough to limit the usefulness of the technique. With differing premedication regimens before the use of Amipaque and with the development of even lower toxicity water-soluble contrast agents, this disadvantage should be readily overcome. Amipaque CTV seems a simple and reliable method to evaluate the functioning of a ventricular shunt system. In the clinical situation in which a shunt malfunction is suspected and previous CT scans are not available or the comparison CT findings are not definitive, ventricular persistence of Amipaque and the absence of abdominal contrast media (if the shunt is totally obstructed distally) confirm the presence of malfunction. A combination of Amipaque CTC 9 and/or Amipaque CTV 1~has proven the most useful diagnostic approach to intracranial cysts. Angiography provides mainly anatomical information. Pneumoencephalography is of limited physiological usefulness and carries a high morbidity. Routine CT again provides basically morphological data, although the J. Neurosurg. / Volume 48 / June, 1978
visualization of hydrocephalus allows mechanistic suppositions. Amipaque CTC or CTV present both precise morphological (such as extra-axial location of cyst) and functional (such as Dandy-Walker versus posterior fossa extra-axial cyst; delayed communication of cyst) information in a single, rapidly performed study. In addition, the circulation of the CSF, the mechanism of the hydrocephalus, and the functioning of a therapeutic shunt may also be defined by this single test. It appears that the use ofpneumoencephalography, angiography, and radionuclide studies may be obviated in the diagnostic evaluation of most brain cysts. Acknowledgments
We wish to acknowledge Jeane Dobrinski for her secretarial assistance, the Departments of Neurology and Neurosurgery for their excellent patient care, and the Neuroradiology Staff (Z. L. Deeb, W. O. Bank, E. R. Heinz, P. B. Markarian, and J. A. Horton) for their assistance and encouragement. References
1. AIm6n T: Contrast agent design. Some aspects of the synthesis of water soluble contrast agents of low osmolality. J Theoret Biol 24: 216-226, 1969 2. Ambrose J" Computerized transverse axial scanning (tomography): Part 2. Clinical application. Br J Radiol 46:1023-1047, 1973 3. Ashburn WL, Harbert JC, Briner WH, et al: Cerebrospinal fluid rhinorrhea studied with the gamma scintillation camera. J Nucl Med 9:523-529, 1968 4. Conway J J, Yarzagaray L, Welch D: Radionuclide evaluation of the Dandy-Walker malformation and congenital arachnoid cyst of the posterior fossa. Am J Roentgenoi Radium Ther Nucl Med 112:306-314, 1971 5. Di Chiro G: Movement of the cerebrospinal fluid in human beings. Nature 204:290-291, 1964
6. Di Chiro G, Reames PM, Mathews WB Jr: RISA-ventriculography and RISA-cisternography. Neurology 14:185-191, 1964 7. Drayer BP, Rosenbaum AE: Amipaque brain penetrance. Its correlation with adverse reactions and value radiodiagnostically. Acta Radiol (Supp!) (In press) 8. Drayer BP, Rosenbaum AE, Higman HB: Cerebrospinal fluid imaging using serial metrizamide CT cisternography. Neuroradiology 13:7-17, 1977 955
B. P. Drayer and A. E. Rosenbaum 9. Drayer BP, Rosenbaum AE, Maroon JC, et al: Posterior foSsa extraaxial cyst: Diagnosis with metrizamide CT cisternography. Am J Roentgenol 128:431-436, 1977 I0. Drayer BP, Rosenbaum AE, Strand RD, et al: Amipaque CT ventriculography. Diagnostic applications. Paper presented at the 15th Annual Meeting of the American Society of Neuroradiology, Hamilton, Bermuda, March, 1977 11. Gado MH, Coleman RE, Lee KS, et al: Correlation between computerized transaxial tomography and radionuclide cisternography in dementia. Neurology 26:555-560, 1976 12. Gilday DL, Kellam J: ~11In-DTPA evaluation of CSF diversionary shunts in children. J Nucl Med 14:920-923, 1973 13. Greitz T, Hindmarsh T: Computer assisted tomography of intracranial CSF circulation using a water-soluble contrast medium. Acta Radioi (Diagn) 15:497-507, 1974 14. Hounsfield GN: Computerized transverse axial scanning (tomography): Part 1. Description of system. Br J Radiol 46:1016-1022, 1973 15. James AE Jr, New PFJ, Heinz ER, et al: A cisternographic classification of hydrocepha-
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16.
17. 18. 19.
lus. Am J Roentgenol Radium Ther Nucl Med 115:39-49, 1972 McAfee IG, Subramanian G: Radioactive agents for imaging, in Freeman LM, Johnson PM (eds): Clinical Scintillation Imaging, ed 2. New York: Grune and Stratton, 1975, pp 13-114 Metrizamide: Metrizamide. A non-ionic water-soluble contrast medium. Acta Radiol (Suppl) 335:1-390, 1973 Naidich TP, Epstein F, Lin JP, et al: Evaluation of pediatric hydrocephalus by computed tomography. Radiology 119:337-353, 1976 Wylie IG, Afshar F, Koeze TH: Results of the use of a new water-soluble contrast medium (metrizamide) in the posterior fossa of the baboon. Br J Radiol 48:1007-1012, 1975
Address reprint requests to: Burton P. Drayer, M.D., Department of Radiology, University of Pittsburgh School of Medicine, Presbyterian-University Hospital, 230 Lothrop Street, Pittsburgh, Pennsylvania 15261.
J. Neurosurg. / Volume 48 /June, 1978
