J Neurosurg 72:378-382, 1990
Diagnosis and microsurgical approach to far-lateral disc herniation in the lumbar spine JOSEPH C. MAROON, M . D . , THOMAS A. KOPITNIK, M . D . , LARRY A. SCHULHOF, M . D . , ADNAN ABEA, M . D . , AND JAMES E. WIEBERGER, M . D .
Department of Neurosurgery, Allegheny General Hospital, Pittsburgh, Pennsylvania; Department of Neurosurgery, West Virginia University Medical Center, Morgantown, West Virginia; and Memorial Mission Hospital, Asheville, North Carolina u," Lumbar-disc herniations that occur beneath or far lateral to the intervertebral facet joint are increasingly recognized as a cause of spinal nerve root compression syndromes at the upper lumbar levels. Failure to diagnose and precisely localize these herniations can lead to unsuccessful surgical exploration or exploration of the incorrect interspace. If these herniations are diagnosed, they often cannot be adequately exposed through the typical midline hemilaminectomy approach. Many authors have advocated a partial or complete unilateral facetectomy to expose these herniations, which can lead to vertebral instability or contribute to continued postoperative back pain. The authors present a series of 25 patients who were diagnosed as having far lateral lumbar disc herniations and underwent paramedian microsurgical lumbar-disc excision. Twelve of these were at the L4-5 level, six at the L5-S 1 level, and seven at the L3-4 level. In these cases, myelography is uniformly normal and high-quality magnetic resonance images may not be helpful. High-resolution computerized tomography (CT) appears to be the best study, but even this may be negative unless enhanced by performing CT-discography. Discography with enhanced CT is ideally suited to precisely diagnose and localize these far-lateral herniations. The paramedian muscle splitting microsurgical approach was found to be the most direct and favorable anatomical route to herniations lateral to the neural foramen. With this approach, there is no facet destruction and postoperative pain is minimal. Patients were typically discharged on the 3rd or 4th postoperative day. The clinical and radiographic characteristics of far-lateral lumbar-disc herniations are reviewed and the paramedian microsurgical approach is discussed. KEY WORDS ~ intervertebral disc discectomy 9 surgical approach
R-LATERAL l u m b a r - d i s c h e r n i a t i o n s b e n e a t h or ateral to t h e facet j o i n t o c c u r with a frequency e t w e e n 2.6% a n d 11.7% o f all l u m b a r - d i s c h e r n i a t i o n s . 1'2'12'16'17'19,22,24'25,3~ A b d u l l a h , et al., 1 rep o r t e d the clinical characteristics w h i c h distinguish t h e m f r o m t h e t y p i c a l h e r n i a t i o n s t h a t o c c u r m e d i a l to t h e facet. U p p e r l u m b a r r o o t c o m p r e s s i o n s y n d r o m e s are f o u r t i m e s m o r e likely to be c a u s e d b y far-lateral disc h e r n i a t i o n s t h a n b y h e r n i a t i o n o f discs a b o v e the L 4 - 5 interspace, w h i c h h a v e a n average i n c i d e n c e o f o n l y 2 . 5 % . 4"14'27'31'35
T h e s t a n d a r d m i d l i n e surgical a p p r o a c h for lateral disc r u p t u r e s i n c l u d e s p a r t i a l l a m i n e c t o m y a n d medial f a c e t e c t o m y in m o s t series, 1'2'16,17'22 with c o m p l e t e face t e c t o m y u s u a l l y reserved for t h o s e disc h e r n i a t i o n s t h a t c a n n o t b e r e a c h e d with a m o r e l i m i t e d proce-
378
9 lateral disc herniation
9 paramedian approach
9
dure. 1,3,16,2z,3~ Z i n d r i c k , et al., 42 a n d R e u l e n , et a/., 32 have d e s c r i b e d a p a r a s p i n a l o r lateral e x p o s u r e which avoids m e d i a l f a c e t e c t o m y a n d possible spinal instability. W e a d v o c a t e a s i m i l a r t e c h n i q u e with e m p h a s i s o n microsurgical a n a t o m y in the intertransverse process region a n d precise p r e o p e r a t i v e localization o f the disc herniation using high-resolution computerized tomogr a p h y (CT), m a g n e t i c r e s o n a n c e ( M R ) imaging, o r C T enhanced discography. Summary of Cases
Presentation a n d Diagnosis In o u r series, 25 p a t i e n t s presented with far-lateral l u m b a r - d i s c h e r n i a t i o n s c o n f i r m e d at surgery. Twelve h e r n i a t i o n s were p r e s e n t at the L 4 - 5 interspace, six
J. Neurosurg. / Volume 72/March, 1990
Paramedian approach to lateral microdiscectomy
FIG. 1. Left: Unenhanced computerized tomography (CT) scan showing questionable far-lateral disc herniation. Right: Discography-enhanced CT scan showing far-lateral disc herniation (arrow).
patients presented with lateral L5-S 1 herniations, and seven patients had a lateral disc herniation at the L3-4 interspace. Nineteen patients (76%) had a positive Lasrgue sign and often presented with pain radiating into the ipsilateral hip. Quadriceps weakness or atrophy was present in 78% of patients with L 3 - 4 herniations and the patellar reflex was depressed or absent in all but one patient with herniations at this level. Fifteen disc lesions were on the left and 10 were on the right. The patients' mean age at diagnosis was 55 years. The diagnosis of far-lateral disc herniation was made using high-resolution CT with and without intrathecal contrast material, surface-coil M R imaging, or CTenhanced discography. The latter method was the most reliable in confirming the diagnosis and in precisely localizing the pathology (Fig. 1). All patients were operated on using the paramedian muscle-splitting microsurgical approach described below. At surgery, 23 of the patients (92%) were found to have a free fragment compressing the affected nerve root, while three had bulging discs and foraminal stenosis. The only complication was the development of burning dysesthesias in the distribution of the regional dorsal root ganglion in four patients, which persisted only briefly in the postoperative period.
Operative Technique Following induction of general endotracheal anesthesia, the patient is placed in the prone position on a lumbar frame. The operative site is prepared in the usual fashion. A paramedian skin incision, approximately 4 cm from the midline and 4 to 5 cm long, is used for a direct paramedian muscle-splitting approach to the far-lateral herniated disc (Fig. 2). The subcutaneous tissue is dissected free from the underlying fascia and the groove between the multifidus and longissimus muscles is palpated (Fig. 3 left). A fascial incision is made at this point and blunt dissection is used to palpate and expose the lateral aspect of the zygapophysial facet joint and the transverse process above and below the disc level to be explored. One or two deep Williams microdiscectomy retractors are used to maintain exposure. It is essential at this point to obtain a
J. Neurosurg. / Volume 72/March, 1990
FIG. 2. Artist's drawing showing the location of the skin incision.
radiograph with a probe in position to confirm the correct interspace. After x-ray confirmation, the operating microscope is used to continue the exposure and dissection. The attachment of the multifldus muscle to the mammillary process of the facet is released and the intertransverse muscle is identified and divided, thus exposing the intertransverse fascia. The intertransverse fascia is divided using microsurgical techniques. There is frequently additional fat that must be dissected to identify the radicular artery and vein, the nerve root, and the dorsal root ganglion (Fig. 3 right). Often the exposure is too far lateral and one must continue to work medially to expose the nerve root but care must be taken to avoid traumatizing it or transmitting electrical energy from the coagulation apparatus to the underlying root and ganglion. Painful postoperative dysesthesias may occur secondary to the trauma of dissection and/or coagulation. This occurred in four of our patients, but fortunately was transient. The nerve root may be additionally vulnerable because it may be splayed over the underlying herniation which is usually medial and superior to the disc space. Caudal migration is prevented by the pedicle in most cases. With preoperative CT localization, disc fragments are precisely located and removed using small pituitary grasping instrumentation. Nerve root manipulation is avoided with the aid of microsurgical techniques. Additional medial exposure may be obtained by removing the lateral margin of the facet joint with no compromise of facet integrity. Once the fragment of disc is removed, the disc space is palpated and additional disc material is removed from the disc space with down-biting pituitary rongeurs. Complete hemostasis is obtained and the fascia, subcutaneous tissue, and skin are closed in layers in the usual manner. 379
J. C. Maroon, et al.
FIG. 3. Artist's drawings showing the muscle groove with fascial incision (left) and the nerve root stretched over the underlying herniated disc fragment (right).
Discussion The incidence of far-lateral lumbar-disc herniations is approximately 10% of all lumbar-disc herniations. 2 Inability to recognize these lesions results in failure to diagnose disabling pain. The diagnosis o f far-lateral disc herniations has remained elusive because of the atypical clinical presentation and the inconsistent radiographic findings with standard studies normally successful for medial herniations.
Clinical Findings Diagnosis and treatment of these herniations is problematic in m a n y respects. The clinical diagnosis relies on a high index o f suspicion coupled with characteristic findings. The clinical presentation o f patients with farlateral disc herniations has subtleties which m a y distinguish these entities from medial herniations. Although any adult age group can be affected, most series describe a slightly older population than seen with central herniations, with average ages ranging from 44 to 57 years. 1,25,26,42These herniations produce pain and radicular s y m p t o m s but, unlike medially located fragments, lateral disc herniations compress the nerve root exiting at the same interspace, and produce upper l u m b a r root compression syndromes. Hip and leg pain are generally present, but groin and anterior thigh pain m a y dominate the clinical picture and are often reproduced by lateral bending. Severe radicular s y m p t o m s more intense than typically seen with central herniations may 380
occur because o f direct compression of the posterior spinal root ganglion. This is in contrast to medial disc herniations, which usually compress nerve roots exiting at the next lowest interspace. Las6gue sign is negative in m a n y series, ~,2,~3,3~ although herniations at lower levels m a y produce a positive straight-leg raising sign. ~3,~5 This is likely due to increased m o v e m e n t of the nerve roots at the lower lumbar levels. 9 The most c o m m o n findings are quadriceps weakness, decreased patellar reflex, and decreased sensation in the L-4 dermatome, since the most c o m m o n level for these herniations is the L 4 - 5 disc space 2'j5'28'42(Table 1).
Radiographic Studies Radiographic diagnosis of lateral lumbar-disc herniations has been shown to be unreliable when using typical studies. Herniations outside the neural foramen are usually not detected at myelography and are often overlooked with high-resolution CT or surface-coil M R imaging. Osborn, et al., 28 found that one-third of farlateral herniations have an initial misdiagnosis. Highresolution C T studies of lateral, foraminal, or extraforaminal herniation is dependent on differential densities of the disc material, nerve roots, epidural fat, and the thecal sac. 23'4j When the disc is isodense, it is difficult to demonstrate with CT. 10,11,33,3s Jackson and Glah ~5 studied a series o f patients with foraminal or extraforaminal l u m b a r disc herniations using metrizamide myelography, CT, discography, and CT-enhanced disJ. Neurosurg. / Volume 72/March, 1990
Paramedian approach to lateral microdiscectomy TABLE 1 Level of far-lateral disc herniation
Authors & Year
L 1-2
L2-3
L3-4
L4-5
L5-S 1
Abdullah, et al., 1974 Nelson & Gold, 1983 Godersky, et al., 1984 Epstein, et al., 1986 Kurobane, et al., 1986 Jackson & Glah, 1987 Zindrick, et al., 1987 Osborn, et aL, 1988 Maroon, et al., 1990 totals
1 0 0 0 0 0 0 0 0 1 (0.3%)
11 0 0 0 0 0 0 6 0 17 (5.4%)
35 0 2 4 1 4 7 17 7 77 (25%)
82 2 5 5 6 8 25 19 12 164 (52%)
9 8 5 3 4 4 7 8 6 54 (17%)
cography. Accurate diagnosis of lateral disc herniations was made with CT-enhanced discography in 94% of cases compared to 38% with discography alone, 50% with CT and/or myelographically enhanced CT, and 13% with myelography alone. Myelographically enhanced CT showed no lesions that were not readily apparent on plain CT; however, discographically enhanced CT may greatly improve the diagnostic accuracy of CT in these cases. The technique of discography was developed in the early 1940's by Lindblom 2~ and applied to CT scanning of the lumbar spine by Angtuaco, et al. 3 This technique is especially helpful as a diagnostic adjunct when myelography is normal or nondiagnostic and]or the clinical picture is misleading. Although Angtuaco, et al., emphasized the lateral oblique approach to discography, Jackson and Glah ~5 found that the posterior midline approach is accomplished easily, with less pain, and less radiation to patient and physician. Watersoluble contrast agents such as Amipaque or Conray60 are superior to oil-based Pantopaque because of the hydrophilic property of nuclear material and the ability of the fragments to rapidly absorb the contrast agents.15 After this, CT can be used to precisely localize the enhanced disc material (Fig. 1 right). This procedure is extremely helpful in differentiating the potential lesions that can be seen lateral to the neural foramen from herniated disc material. This differential diagnosis includes conjoined nerve roots, enlarged ganglion, neurofibroma, primary schwannoma, and metastatic neoplasm, as well as herniated disc. 5"7'12'37'4~ Surgical Approach
Presently, the most c o m m o n surgical approach is via a midline hemilaminectomy exposure, often necessitating destruction of the ipsilateral facet joint. ~-3,6,15-17.22.42 Instability following facetectomy has been reported to occur with alarming frequency during decompressive laminectomies and is a cause for concern during disc e x p l o r a t i o n . 18'32'36'39 Several authors have advocated a lateral dissection along the facet through a midline incision, with partial lateral facet resection if necessary. 12'29'34'42 This approach requires adequate lateral J. Neurosurg. / V o l u m e 7 2 / M a r c h , 1990
Total Cases 138 10 12 12 11 16 39 50 25 313
retraction to pass anteriorly over the facet joint. The need for this difficult lateral retraction is eliminated by using the paramedian muscle-splitting approach. With this technique, the dissection remains immediately lateral to the facet joint, and retraction is minimized. The spinal nerve and ganglion are directly beneath the intertransverse ligament, and microsurgical technique greatly aids in the dissection when opening the ligament and working near the nerve root. With this approach and microtechnique, there is minimal resection of bone and facet joint and little risk of injury to neural structures. Following removal of the herniated fragments, the disc space can be adequately cleared. This approach can easily be combined with the classic interlaminar exposure if more medial exploration is required. We believe that microtechnique is essential in the region lateral to the facet joint to avoid manipulation and injury to the neural and vascular structures, especially the dorsal root ganglion. Thermal or mechanical injury to the ganglion may result in postoperative dysesthetic pain. This muscle-splitting approach is the most direct and favorable anatomical route to lumbardisc herniations lateral to the neural foramen, and is greatly facilitated by the use of appropriate microsurgical techniques. References 1. Abdullah AF, Ditto EW III, Byrd EB, et al: Extremelateral lumbar disc herniations. Clinical syndrome and special problems of diagnosis. J Neurosurg 41:229-234, 1974 2. Abdullah AF, Wolber PGH, Warfield JR, et al: Surgical management of extreme lateral lumbar disc herniations: review of 138 cases. Neurosurgery 22:648-653, 1988 3. Angtuaco EJC, Holder JC, Boop WC, et al: Computed tomographic discography in the evaluation of extreme lateral disc herniation. Neurosurgery 14:350-352, 1984 4. Brown HA, Pont ME: Disease of lumbar discs. Ten years of surgical treatment. J Neurosurg 20:410-417, 1963 5. Brown LJ: Definitive diagnosis of extreme lateral lumbar disc herniation. Surg Neurol 27:373-376, 1987 6. Echols DH, Rehfeldt FC: Failure to disclose ruptured inteivertebral disks in 32 operations for sciatica. J Neurosurg 6:376-382, 1949 7. Eckarot J J, Kaplan DD, Batzdorf U, et al: Extraforaminal 381
J. C. Maroon, et al.
8. 9.
10. 11. 12. 13. 14.
15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.
26. 27.
382
disc herniation simulating a retroperitoneal neoplasm. J Bone Joint Surg (Am) 67:1275-1277, 1985 Epstein NE, Epstein JA, Carras R, et al: Far lateral lumbar disc herniation: diagnosis and surgical management. Neuroorthopedics 1:37-44, 1986 Falcon MA, McGeorge M, Begg AC: Observations on the cause and mechanisms of symptom-production in sciatica and low back pain. J Neuroi Neurosurg Psychiatry 11: 13-26, 1948 Firooznia H, Benjamin V, Kricheff II, et al: CT of lumbar spine disk herniation: correlation with surgical findings. A J R 142:587-592, 1984 Fries JW, Abodeely DA, Vijungco JG, et al: Computed tomography of herniated and extruded nucleus pulposus. J Comput Assist Tomogr 6:874-887, 1982 Gado M, Patel J, Hodges FJ: Lateral disk herniation into the lumbar intervertebral foramen: differential diagnosis. A J N R 4:598-600, 1983 Godersky JC, Erickson DL, Seljeskog EL: Extreme lateral disc herniation: diagnosis by computed tomographic scanning. Neurosurgery 14:549-552, 1984 Gurdjian ES, Ostrowski AZ, Hardy WG, et al: Results of operative treatment of protruded and ruptured lumbar discs. Based on 1176 operative cases with 82 per cent follow-up of 3 to 13 years. J Neurosurg 18:783-791, 1961 Jackson RP, Glah J J: Foraminal and extraforaminal lumbar disc herniation: diagnosis and treatment. Spine 12: 577-585, 1987 Kornberg M: Extreme lateral lumbar disc herniations: clinical syndrome and computed tomography recognition. Spine 12:586-589, 1987 Kurobane Y, Takahashi T, Tajima T, et al: Extraforamenal disc herniation. Spine 11:260-268, 1986 Lee CK: Lumbar spinal instability (olisthesis) after extensive posterior spinal decompression. Spine 8:429-433, 1983 Leonardi M, Biasizzo E, Fabris G, et al: CT evaluation of the lumbosacral spine. A J N R 4:846-847, 1983 Lindblom K: Protrusions of disks and nerve compression in the lumbar region. Acta Radiol 25:195-212, 1944 Lindblom K: Techniques and results in myelography and disc puncture. Aeta Radiol 34:321-330, 1950 Macnab I: Negative disc exploration. An analysis of the causes of nerve-root involvement in sixty-eight patients, J Bone Joint Surg (Am) 53:891-903, 1971 Mikhael MA: High resolution computed tomography in the diagnosis of laterally herniated lumbar discs. Comput Radiol 7:161-166, 1983 Motateanu M, Fankhauser H, Mansouri B, et al: La bernie discale lombaire extrrmement latrrale. A p r o p o s d'une srrie de 25 cas. Neurochirurgie 32:74-80, 1986 Nelson M J, Gold LH: CT evaluation of intervertebral foramina lesions with normal or non-diagnostic myelograms. Report of ten cases. Comput Radiol 7:155-160, 1983 Novetsky G J, Berlin L, Epstein JA, et al: The extraforaminal herniated disc: detection by computed tomography. A J N R 3:653-655, 1982 O'Connell JE: Protrusions of the lumbar intervertebral
28. 29. 30. 31. 32.
33. 34. 35. 36.
37. 38.
39. 40. 41. 42.
discs: clinical review based on five hundred cases treated by excision of the protrusion (Hunterian Lecture). J Bone Joint Snrg (Br) 33:8-30, 1951 Osborn AG, Hood RS, Sherry RG, et al: CT/MR spectrum of far lateral and anterior lumbosacral disk herniations. A J N R 9:775-778, 1988 Osgood CP, Dujovny M, Faille R, et al: Microsurgical ganglionectomy for chronic pain syndromes. Technical note. J Neurosurg 45:113-115, 1976 Patrick BS: Extreme lateral ruptures of lumbar intervertebral discs. Surg Neurol 3:301-304, 1975 Raaf J: Some observations regarding 905 patients operated upon for protruded lumbar intervertebral disc. Am J Surg 97:388-399, 1959 Reulen H J, Pfaundler S, Ebeling U: The lateral microsurgical approach to the "extracanalicular" lumbar disc herniation. I: A technical note. Aeta Neuroehir 84:64-67, 1987 Schubiger O, Valavanis A, Hollmann J: Computed tomography of the intervertebral foramen. Neuroradiology 26:439-444, 1984 Scoville WB: Extradural spinal sensory rhizotomy. J Neurosurg 25:94-95, 1966 Semmes RE: Ruptures of the Lumbar Intravertebral Disc. Springfield, Ill: Charles C Thomas, 1964 Shenkin HA, Hash C J: Spondylolisthesis after multiple bilateral laminectomies and facetectomies for lumbar spondylosis. Follow-up review. J Neurosurg 50:45-47, 1979 Sim FH, Dahlia DC, Stauffer RN, et al: Primary bone tumors simulating lumbar disc syndrome. Spine 2: 65-74, 1977 Spanu G, Rodriguez y Baena, Rainold F: Reliability of clinical examination and computed tomography in the diagnosis of extreme lateral disc herniation. Neurochirurgia 30:112-114, 1987 White AA III, Panjabi MM: The Problem of Clinical Instability in the Human Spine: A Systematic Approach. Philadelphia: JB Lippincott, 1978, pp 251-264 Wilkes LL, Cannon CL, Ham OE: Malignant tumors of the pelvic girdle mimicking the herniated disc syndrome. Clin Orthop 138:217-221, 1979 Williams AL, Haughton VM, Daniels DL, et al: CT recognition of lateral lumbar disc herniation. A J N R 3: 211-213, 1982 Zindrick MR, Wiltse LL, Rauschning W: Disc herniations lateral to the intervertebral foramen, in White AH, Rothman RH, Ray CD (eds): Lumbar Spine Surgery. London: CV Mosby, 1987, pp 195-207
Manuscript received July 13, 1989. Address for Dr. Kopitnik: Department of Neurosurgery, West Virginia University, Medical Center, Morgantown, West Virginia. Address for Dr. Schulhof: Memorial Mission Hospital, Asheville, North Carolina. Address reprint requests to: Joseph C. Maroon, M.D., Allegheny General Hospital, Department of Neurosurgery, Pittsburgh, Pennsylvania 15212.
J. Neurosurg. / Volume 7 2 / M a r c h , 1990
Diagnosis and microsurgical approach to far-lateral disc herniation in the lumbar spine JOSEPH C. MAROON, M . D . , THOMAS A. KOPITNIK, M . D . , LARRY A. SCHULHOF, M . D . , ADNAN ABEA, M . D . , AND JAMES E. WIEBERGER, M . D .
Department of Neurosurgery, Allegheny General Hospital, Pittsburgh, Pennsylvania; Department of Neurosurgery, West Virginia University Medical Center, Morgantown, West Virginia; and Memorial Mission Hospital, Asheville, North Carolina u," Lumbar-disc herniations that occur beneath or far lateral to the intervertebral facet joint are increasingly recognized as a cause of spinal nerve root compression syndromes at the upper lumbar levels. Failure to diagnose and precisely localize these herniations can lead to unsuccessful surgical exploration or exploration of the incorrect interspace. If these herniations are diagnosed, they often cannot be adequately exposed through the typical midline hemilaminectomy approach. Many authors have advocated a partial or complete unilateral facetectomy to expose these herniations, which can lead to vertebral instability or contribute to continued postoperative back pain. The authors present a series of 25 patients who were diagnosed as having far lateral lumbar disc herniations and underwent paramedian microsurgical lumbar-disc excision. Twelve of these were at the L4-5 level, six at the L5-S 1 level, and seven at the L3-4 level. In these cases, myelography is uniformly normal and high-quality magnetic resonance images may not be helpful. High-resolution computerized tomography (CT) appears to be the best study, but even this may be negative unless enhanced by performing CT-discography. Discography with enhanced CT is ideally suited to precisely diagnose and localize these far-lateral herniations. The paramedian muscle splitting microsurgical approach was found to be the most direct and favorable anatomical route to herniations lateral to the neural foramen. With this approach, there is no facet destruction and postoperative pain is minimal. Patients were typically discharged on the 3rd or 4th postoperative day. The clinical and radiographic characteristics of far-lateral lumbar-disc herniations are reviewed and the paramedian microsurgical approach is discussed. KEY WORDS ~ intervertebral disc discectomy 9 surgical approach
R-LATERAL l u m b a r - d i s c h e r n i a t i o n s b e n e a t h or ateral to t h e facet j o i n t o c c u r with a frequency e t w e e n 2.6% a n d 11.7% o f all l u m b a r - d i s c h e r n i a t i o n s . 1'2'12'16'17'19,22,24'25,3~ A b d u l l a h , et al., 1 rep o r t e d the clinical characteristics w h i c h distinguish t h e m f r o m t h e t y p i c a l h e r n i a t i o n s t h a t o c c u r m e d i a l to t h e facet. U p p e r l u m b a r r o o t c o m p r e s s i o n s y n d r o m e s are f o u r t i m e s m o r e likely to be c a u s e d b y far-lateral disc h e r n i a t i o n s t h a n b y h e r n i a t i o n o f discs a b o v e the L 4 - 5 interspace, w h i c h h a v e a n average i n c i d e n c e o f o n l y 2 . 5 % . 4"14'27'31'35
T h e s t a n d a r d m i d l i n e surgical a p p r o a c h for lateral disc r u p t u r e s i n c l u d e s p a r t i a l l a m i n e c t o m y a n d medial f a c e t e c t o m y in m o s t series, 1'2'16,17'22 with c o m p l e t e face t e c t o m y u s u a l l y reserved for t h o s e disc h e r n i a t i o n s t h a t c a n n o t b e r e a c h e d with a m o r e l i m i t e d proce-
378
9 lateral disc herniation
9 paramedian approach
9
dure. 1,3,16,2z,3~ Z i n d r i c k , et al., 42 a n d R e u l e n , et a/., 32 have d e s c r i b e d a p a r a s p i n a l o r lateral e x p o s u r e which avoids m e d i a l f a c e t e c t o m y a n d possible spinal instability. W e a d v o c a t e a s i m i l a r t e c h n i q u e with e m p h a s i s o n microsurgical a n a t o m y in the intertransverse process region a n d precise p r e o p e r a t i v e localization o f the disc herniation using high-resolution computerized tomogr a p h y (CT), m a g n e t i c r e s o n a n c e ( M R ) imaging, o r C T enhanced discography. Summary of Cases
Presentation a n d Diagnosis In o u r series, 25 p a t i e n t s presented with far-lateral l u m b a r - d i s c h e r n i a t i o n s c o n f i r m e d at surgery. Twelve h e r n i a t i o n s were p r e s e n t at the L 4 - 5 interspace, six
J. Neurosurg. / Volume 72/March, 1990
Paramedian approach to lateral microdiscectomy
FIG. 1. Left: Unenhanced computerized tomography (CT) scan showing questionable far-lateral disc herniation. Right: Discography-enhanced CT scan showing far-lateral disc herniation (arrow).
patients presented with lateral L5-S 1 herniations, and seven patients had a lateral disc herniation at the L3-4 interspace. Nineteen patients (76%) had a positive Lasrgue sign and often presented with pain radiating into the ipsilateral hip. Quadriceps weakness or atrophy was present in 78% of patients with L 3 - 4 herniations and the patellar reflex was depressed or absent in all but one patient with herniations at this level. Fifteen disc lesions were on the left and 10 were on the right. The patients' mean age at diagnosis was 55 years. The diagnosis of far-lateral disc herniation was made using high-resolution CT with and without intrathecal contrast material, surface-coil M R imaging, or CTenhanced discography. The latter method was the most reliable in confirming the diagnosis and in precisely localizing the pathology (Fig. 1). All patients were operated on using the paramedian muscle-splitting microsurgical approach described below. At surgery, 23 of the patients (92%) were found to have a free fragment compressing the affected nerve root, while three had bulging discs and foraminal stenosis. The only complication was the development of burning dysesthesias in the distribution of the regional dorsal root ganglion in four patients, which persisted only briefly in the postoperative period.
Operative Technique Following induction of general endotracheal anesthesia, the patient is placed in the prone position on a lumbar frame. The operative site is prepared in the usual fashion. A paramedian skin incision, approximately 4 cm from the midline and 4 to 5 cm long, is used for a direct paramedian muscle-splitting approach to the far-lateral herniated disc (Fig. 2). The subcutaneous tissue is dissected free from the underlying fascia and the groove between the multifidus and longissimus muscles is palpated (Fig. 3 left). A fascial incision is made at this point and blunt dissection is used to palpate and expose the lateral aspect of the zygapophysial facet joint and the transverse process above and below the disc level to be explored. One or two deep Williams microdiscectomy retractors are used to maintain exposure. It is essential at this point to obtain a
J. Neurosurg. / Volume 72/March, 1990
FIG. 2. Artist's drawing showing the location of the skin incision.
radiograph with a probe in position to confirm the correct interspace. After x-ray confirmation, the operating microscope is used to continue the exposure and dissection. The attachment of the multifldus muscle to the mammillary process of the facet is released and the intertransverse muscle is identified and divided, thus exposing the intertransverse fascia. The intertransverse fascia is divided using microsurgical techniques. There is frequently additional fat that must be dissected to identify the radicular artery and vein, the nerve root, and the dorsal root ganglion (Fig. 3 right). Often the exposure is too far lateral and one must continue to work medially to expose the nerve root but care must be taken to avoid traumatizing it or transmitting electrical energy from the coagulation apparatus to the underlying root and ganglion. Painful postoperative dysesthesias may occur secondary to the trauma of dissection and/or coagulation. This occurred in four of our patients, but fortunately was transient. The nerve root may be additionally vulnerable because it may be splayed over the underlying herniation which is usually medial and superior to the disc space. Caudal migration is prevented by the pedicle in most cases. With preoperative CT localization, disc fragments are precisely located and removed using small pituitary grasping instrumentation. Nerve root manipulation is avoided with the aid of microsurgical techniques. Additional medial exposure may be obtained by removing the lateral margin of the facet joint with no compromise of facet integrity. Once the fragment of disc is removed, the disc space is palpated and additional disc material is removed from the disc space with down-biting pituitary rongeurs. Complete hemostasis is obtained and the fascia, subcutaneous tissue, and skin are closed in layers in the usual manner. 379
J. C. Maroon, et al.
FIG. 3. Artist's drawings showing the muscle groove with fascial incision (left) and the nerve root stretched over the underlying herniated disc fragment (right).
Discussion The incidence of far-lateral lumbar-disc herniations is approximately 10% of all lumbar-disc herniations. 2 Inability to recognize these lesions results in failure to diagnose disabling pain. The diagnosis o f far-lateral disc herniations has remained elusive because of the atypical clinical presentation and the inconsistent radiographic findings with standard studies normally successful for medial herniations.
Clinical Findings Diagnosis and treatment of these herniations is problematic in m a n y respects. The clinical diagnosis relies on a high index o f suspicion coupled with characteristic findings. The clinical presentation o f patients with farlateral disc herniations has subtleties which m a y distinguish these entities from medial herniations. Although any adult age group can be affected, most series describe a slightly older population than seen with central herniations, with average ages ranging from 44 to 57 years. 1,25,26,42These herniations produce pain and radicular s y m p t o m s but, unlike medially located fragments, lateral disc herniations compress the nerve root exiting at the same interspace, and produce upper l u m b a r root compression syndromes. Hip and leg pain are generally present, but groin and anterior thigh pain m a y dominate the clinical picture and are often reproduced by lateral bending. Severe radicular s y m p t o m s more intense than typically seen with central herniations may 380
occur because o f direct compression of the posterior spinal root ganglion. This is in contrast to medial disc herniations, which usually compress nerve roots exiting at the next lowest interspace. Las6gue sign is negative in m a n y series, ~,2,~3,3~ although herniations at lower levels m a y produce a positive straight-leg raising sign. ~3,~5 This is likely due to increased m o v e m e n t of the nerve roots at the lower lumbar levels. 9 The most c o m m o n findings are quadriceps weakness, decreased patellar reflex, and decreased sensation in the L-4 dermatome, since the most c o m m o n level for these herniations is the L 4 - 5 disc space 2'j5'28'42(Table 1).
Radiographic Studies Radiographic diagnosis of lateral lumbar-disc herniations has been shown to be unreliable when using typical studies. Herniations outside the neural foramen are usually not detected at myelography and are often overlooked with high-resolution CT or surface-coil M R imaging. Osborn, et al., 28 found that one-third of farlateral herniations have an initial misdiagnosis. Highresolution C T studies of lateral, foraminal, or extraforaminal herniation is dependent on differential densities of the disc material, nerve roots, epidural fat, and the thecal sac. 23'4j When the disc is isodense, it is difficult to demonstrate with CT. 10,11,33,3s Jackson and Glah ~5 studied a series o f patients with foraminal or extraforaminal l u m b a r disc herniations using metrizamide myelography, CT, discography, and CT-enhanced disJ. Neurosurg. / Volume 72/March, 1990
Paramedian approach to lateral microdiscectomy TABLE 1 Level of far-lateral disc herniation
Authors & Year
L 1-2
L2-3
L3-4
L4-5
L5-S 1
Abdullah, et al., 1974 Nelson & Gold, 1983 Godersky, et al., 1984 Epstein, et al., 1986 Kurobane, et al., 1986 Jackson & Glah, 1987 Zindrick, et al., 1987 Osborn, et aL, 1988 Maroon, et al., 1990 totals
1 0 0 0 0 0 0 0 0 1 (0.3%)
11 0 0 0 0 0 0 6 0 17 (5.4%)
35 0 2 4 1 4 7 17 7 77 (25%)
82 2 5 5 6 8 25 19 12 164 (52%)
9 8 5 3 4 4 7 8 6 54 (17%)
cography. Accurate diagnosis of lateral disc herniations was made with CT-enhanced discography in 94% of cases compared to 38% with discography alone, 50% with CT and/or myelographically enhanced CT, and 13% with myelography alone. Myelographically enhanced CT showed no lesions that were not readily apparent on plain CT; however, discographically enhanced CT may greatly improve the diagnostic accuracy of CT in these cases. The technique of discography was developed in the early 1940's by Lindblom 2~ and applied to CT scanning of the lumbar spine by Angtuaco, et al. 3 This technique is especially helpful as a diagnostic adjunct when myelography is normal or nondiagnostic and]or the clinical picture is misleading. Although Angtuaco, et al., emphasized the lateral oblique approach to discography, Jackson and Glah ~5 found that the posterior midline approach is accomplished easily, with less pain, and less radiation to patient and physician. Watersoluble contrast agents such as Amipaque or Conray60 are superior to oil-based Pantopaque because of the hydrophilic property of nuclear material and the ability of the fragments to rapidly absorb the contrast agents.15 After this, CT can be used to precisely localize the enhanced disc material (Fig. 1 right). This procedure is extremely helpful in differentiating the potential lesions that can be seen lateral to the neural foramen from herniated disc material. This differential diagnosis includes conjoined nerve roots, enlarged ganglion, neurofibroma, primary schwannoma, and metastatic neoplasm, as well as herniated disc. 5"7'12'37'4~ Surgical Approach
Presently, the most c o m m o n surgical approach is via a midline hemilaminectomy exposure, often necessitating destruction of the ipsilateral facet joint. ~-3,6,15-17.22.42 Instability following facetectomy has been reported to occur with alarming frequency during decompressive laminectomies and is a cause for concern during disc e x p l o r a t i o n . 18'32'36'39 Several authors have advocated a lateral dissection along the facet through a midline incision, with partial lateral facet resection if necessary. 12'29'34'42 This approach requires adequate lateral J. Neurosurg. / V o l u m e 7 2 / M a r c h , 1990
Total Cases 138 10 12 12 11 16 39 50 25 313
retraction to pass anteriorly over the facet joint. The need for this difficult lateral retraction is eliminated by using the paramedian muscle-splitting approach. With this technique, the dissection remains immediately lateral to the facet joint, and retraction is minimized. The spinal nerve and ganglion are directly beneath the intertransverse ligament, and microsurgical technique greatly aids in the dissection when opening the ligament and working near the nerve root. With this approach and microtechnique, there is minimal resection of bone and facet joint and little risk of injury to neural structures. Following removal of the herniated fragments, the disc space can be adequately cleared. This approach can easily be combined with the classic interlaminar exposure if more medial exploration is required. We believe that microtechnique is essential in the region lateral to the facet joint to avoid manipulation and injury to the neural and vascular structures, especially the dorsal root ganglion. Thermal or mechanical injury to the ganglion may result in postoperative dysesthetic pain. This muscle-splitting approach is the most direct and favorable anatomical route to lumbardisc herniations lateral to the neural foramen, and is greatly facilitated by the use of appropriate microsurgical techniques. References 1. Abdullah AF, Ditto EW III, Byrd EB, et al: Extremelateral lumbar disc herniations. Clinical syndrome and special problems of diagnosis. J Neurosurg 41:229-234, 1974 2. Abdullah AF, Wolber PGH, Warfield JR, et al: Surgical management of extreme lateral lumbar disc herniations: review of 138 cases. Neurosurgery 22:648-653, 1988 3. Angtuaco EJC, Holder JC, Boop WC, et al: Computed tomographic discography in the evaluation of extreme lateral disc herniation. Neurosurgery 14:350-352, 1984 4. Brown HA, Pont ME: Disease of lumbar discs. Ten years of surgical treatment. J Neurosurg 20:410-417, 1963 5. Brown LJ: Definitive diagnosis of extreme lateral lumbar disc herniation. Surg Neurol 27:373-376, 1987 6. Echols DH, Rehfeldt FC: Failure to disclose ruptured inteivertebral disks in 32 operations for sciatica. J Neurosurg 6:376-382, 1949 7. Eckarot J J, Kaplan DD, Batzdorf U, et al: Extraforaminal 381
J. C. Maroon, et al.
8. 9.
10. 11. 12. 13. 14.
15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.
26. 27.
382
disc herniation simulating a retroperitoneal neoplasm. J Bone Joint Surg (Am) 67:1275-1277, 1985 Epstein NE, Epstein JA, Carras R, et al: Far lateral lumbar disc herniation: diagnosis and surgical management. Neuroorthopedics 1:37-44, 1986 Falcon MA, McGeorge M, Begg AC: Observations on the cause and mechanisms of symptom-production in sciatica and low back pain. J Neuroi Neurosurg Psychiatry 11: 13-26, 1948 Firooznia H, Benjamin V, Kricheff II, et al: CT of lumbar spine disk herniation: correlation with surgical findings. A J R 142:587-592, 1984 Fries JW, Abodeely DA, Vijungco JG, et al: Computed tomography of herniated and extruded nucleus pulposus. J Comput Assist Tomogr 6:874-887, 1982 Gado M, Patel J, Hodges FJ: Lateral disk herniation into the lumbar intervertebral foramen: differential diagnosis. A J N R 4:598-600, 1983 Godersky JC, Erickson DL, Seljeskog EL: Extreme lateral disc herniation: diagnosis by computed tomographic scanning. Neurosurgery 14:549-552, 1984 Gurdjian ES, Ostrowski AZ, Hardy WG, et al: Results of operative treatment of protruded and ruptured lumbar discs. Based on 1176 operative cases with 82 per cent follow-up of 3 to 13 years. J Neurosurg 18:783-791, 1961 Jackson RP, Glah J J: Foraminal and extraforaminal lumbar disc herniation: diagnosis and treatment. Spine 12: 577-585, 1987 Kornberg M: Extreme lateral lumbar disc herniations: clinical syndrome and computed tomography recognition. Spine 12:586-589, 1987 Kurobane Y, Takahashi T, Tajima T, et al: Extraforamenal disc herniation. Spine 11:260-268, 1986 Lee CK: Lumbar spinal instability (olisthesis) after extensive posterior spinal decompression. Spine 8:429-433, 1983 Leonardi M, Biasizzo E, Fabris G, et al: CT evaluation of the lumbosacral spine. A J N R 4:846-847, 1983 Lindblom K: Protrusions of disks and nerve compression in the lumbar region. Acta Radiol 25:195-212, 1944 Lindblom K: Techniques and results in myelography and disc puncture. Aeta Radiol 34:321-330, 1950 Macnab I: Negative disc exploration. An analysis of the causes of nerve-root involvement in sixty-eight patients, J Bone Joint Surg (Am) 53:891-903, 1971 Mikhael MA: High resolution computed tomography in the diagnosis of laterally herniated lumbar discs. Comput Radiol 7:161-166, 1983 Motateanu M, Fankhauser H, Mansouri B, et al: La bernie discale lombaire extrrmement latrrale. A p r o p o s d'une srrie de 25 cas. Neurochirurgie 32:74-80, 1986 Nelson M J, Gold LH: CT evaluation of intervertebral foramina lesions with normal or non-diagnostic myelograms. Report of ten cases. Comput Radiol 7:155-160, 1983 Novetsky G J, Berlin L, Epstein JA, et al: The extraforaminal herniated disc: detection by computed tomography. A J N R 3:653-655, 1982 O'Connell JE: Protrusions of the lumbar intervertebral
28. 29. 30. 31. 32.
33. 34. 35. 36.
37. 38.
39. 40. 41. 42.
discs: clinical review based on five hundred cases treated by excision of the protrusion (Hunterian Lecture). J Bone Joint Snrg (Br) 33:8-30, 1951 Osborn AG, Hood RS, Sherry RG, et al: CT/MR spectrum of far lateral and anterior lumbosacral disk herniations. A J N R 9:775-778, 1988 Osgood CP, Dujovny M, Faille R, et al: Microsurgical ganglionectomy for chronic pain syndromes. Technical note. J Neurosurg 45:113-115, 1976 Patrick BS: Extreme lateral ruptures of lumbar intervertebral discs. Surg Neurol 3:301-304, 1975 Raaf J: Some observations regarding 905 patients operated upon for protruded lumbar intervertebral disc. Am J Surg 97:388-399, 1959 Reulen H J, Pfaundler S, Ebeling U: The lateral microsurgical approach to the "extracanalicular" lumbar disc herniation. I: A technical note. Aeta Neuroehir 84:64-67, 1987 Schubiger O, Valavanis A, Hollmann J: Computed tomography of the intervertebral foramen. Neuroradiology 26:439-444, 1984 Scoville WB: Extradural spinal sensory rhizotomy. J Neurosurg 25:94-95, 1966 Semmes RE: Ruptures of the Lumbar Intravertebral Disc. Springfield, Ill: Charles C Thomas, 1964 Shenkin HA, Hash C J: Spondylolisthesis after multiple bilateral laminectomies and facetectomies for lumbar spondylosis. Follow-up review. J Neurosurg 50:45-47, 1979 Sim FH, Dahlia DC, Stauffer RN, et al: Primary bone tumors simulating lumbar disc syndrome. Spine 2: 65-74, 1977 Spanu G, Rodriguez y Baena, Rainold F: Reliability of clinical examination and computed tomography in the diagnosis of extreme lateral disc herniation. Neurochirurgia 30:112-114, 1987 White AA III, Panjabi MM: The Problem of Clinical Instability in the Human Spine: A Systematic Approach. Philadelphia: JB Lippincott, 1978, pp 251-264 Wilkes LL, Cannon CL, Ham OE: Malignant tumors of the pelvic girdle mimicking the herniated disc syndrome. Clin Orthop 138:217-221, 1979 Williams AL, Haughton VM, Daniels DL, et al: CT recognition of lateral lumbar disc herniation. A J N R 3: 211-213, 1982 Zindrick MR, Wiltse LL, Rauschning W: Disc herniations lateral to the intervertebral foramen, in White AH, Rothman RH, Ray CD (eds): Lumbar Spine Surgery. London: CV Mosby, 1987, pp 195-207
Manuscript received July 13, 1989. Address for Dr. Kopitnik: Department of Neurosurgery, West Virginia University, Medical Center, Morgantown, West Virginia. Address for Dr. Schulhof: Memorial Mission Hospital, Asheville, North Carolina. Address reprint requests to: Joseph C. Maroon, M.D., Allegheny General Hospital, Department of Neurosurgery, Pittsburgh, Pennsylvania 15212.
J. Neurosurg. / Volume 7 2 / M a r c h , 1990
