Utility of Magnetic Resonance Imaging in the Diagnosis of Intranasal Meningoencephaloceles

The

S. James Zinreich, MD; Jack C. Borders, MD; David W. Douglas E. Mattox, MD; Donlin M. Long, MD; David W. \s=b\

We

present three patients in whom the diagnosis of

made by magnetic meningoencephalocele resonance imaging. The initial clinical evaluation and computed tomographic examinations of these patients failed to distinguish between chronic inflammation and intranasal meningoencephalocele. Although both computed tomography and magnetic resonance imaging are used to distinguish between normal, inflammatory, and neoplastic tissue in the nasal cavity and paranasal sinuses, limitations do exist and these are the focus of our communication. A clear understanding of the efficacy of these radiographic modalities will enhance surgical planning and can preclude severe

intranasal

was

complications. (Arch Otolaryngol Head Neck Surg. 1992;118:1253-1256)

used dis¬

(CT) increasingly being Computed tomography chronic inflammatory patients sinuses.1,2 and is

evaluate of the nasal cavity to

with

paranasal Magnetic resonance imaging (MRI) has shown significant promise in distinguishing normal from inflammatory or neoplastic tis¬ sue.3-4 Both radiographie modalities additionally serve as a "mapping guide" for the surgeon, whose task is to remove inflammatory and neoplastic tissue from this morpholog¬ ically complex region. The anatomic variations inherent to the nasal cavity and paranasal sinuses further add to the complexity of the regional anatomy and make the surgeon's ease

task even more difficult. Paranasal sinus meningoencephaloceles, a common occurrence, can be confused with an inflammatory and/ or neoplastic process, resulting in serious surgical

complications. Congenital anterior and middle cranial meningoenceph¬ aloceles represent 25% of all meningoencephaloceles in approximately 1/16000 patients.5 On CT scans, the atten¬ uations (density appearance) of brain parenchyma in the

Accepted for publication June 8, 1992. From the Neuroradiological Division of the Russell H. Morgan Department of Radiology (Dr Zinreich), the Department of OtolaryngologyHead and Neck Surgery (Drs Borders, Eisele, and Mattox), the Department of Neurosurgery (Dr Long), The Johns Hopkins Medical Institutions, Baltimore, Md; and the Department of Otolaryngology\p=n-\Headand Neck Surgery, University of Pennsylvania, Philadelphia (Dr Kennedy). Reprint requests to Meyer 8-140, The Johns Hopkins Hospital, 600 N

Wolfe St, Baltimore, MD 21205 (Dr Zinreich).

nasal

Eisele, MD;

Kennedy,

MD

and inflammatory similar and visually indistinguishable. The presence and appearance of bone erosion are a clue to the correct diagnosis. Computed tomography, with its ability to image the fine bony architecture of this region, is essen¬ tial in this respect. In the diagnosis of intranasal menin¬ goencephalocele, however, MRI has three major advan¬ tages over CT: (1) direct orthogonal scanning in virtually any plane; (2) improved soft-tissue resolution; and (3) the choice of various acquisitions to distinguish various tis¬ sues. Consequently, MRI provides the most accurate dis¬ play of meningoencephaloceles that might otherwise be mistaken for inflammatory or neoplastic pathology. The aim of this communication is to show the indications for, and utility of, MRI in the prompt and accurate diagnosis of intranasal meningoencephaloceles.

cavity (meningocele), neoplasm,

mucosa are

REPORT OF CASES CASE 1.—A 48-year-old white man reported to a referring phy¬ sician's office with complaints of a chronic cough, anosmia, left nasal airway obstruction, and purulent rhinorrhea. Approxi¬ mately 18 months prior to presentation, he had sinus surgery of unknown type for "sinus trouble." Following that surgery, he was readmitted on the sixth postoperative day with a severe headache and was hospitalized for a total of 8 days. At presentation, he was found to have a mass obstructing the left nasal airway. The mass was thought to be a polyp originating from the anterior ethmoid roof and was described as white with prominent vasculature and with "less turgor than an allergic polyp." There was also a large amount of mucopus present within the nasal cavity. A CT scan revealed a 3xl.2-cm mass in the left nasal cavity ad¬ jacent to a bone defect in the left cribriform plate. Significant ipsilateral maxillary mucosal thickening was present with no evi¬ dence of ethmoid sinus disease. The nasal septum was deviated to the right. For further definition of the pathologic process an MRI evaluation was performed and revealed that the nasal mass was a meningoencephalocele of the frontal lobe. A frontal craniotomy was subsequently performed. The men¬ ingoencephalocele was amputated, the durai defect repaired, and the bony defect in the anterior cranial fossa reconstructed with a bone graft. The patient's postoperative course was

uncomplicated. Case 2.—A 50-year-old black woman presented to a referring physician with the chief complaint of nasal obstruction. She reported that 6 weeks prior to the onset of her symptoms she had experienced a grand mal seizure, the workup of which was reportedly normal. Standard sinus roentgenograms revealed

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Fig 1.—Computed tomogram (CT) and magnetic resonance image (MRI, of a small meningoencephalocele. Top, Coronal CT ¡mages through the

posterior ethmoid sinus reveal a bony dehiscence within the right fovea ethmoidales (arrow) and a soft-tissue mass in the posterior ethmoid si¬

Center, Axial T,-weighted MRI at the level of the midorbit reveal* soft-tissue mass (arrow) in the posterior ethmoid sinus. With this scan¬ ning plane, one cannot distinguish between a focal inflammatory pro¬ cess and an encephalocele. Bottom, Coronal ,-weighted MRI reveal', herniation of the gyrus rectus (r) and the medial orbital gyrus (I) into the left posterior ethmoid sinus. nus.

a

opacification of the left maxillary sinus as well as a bony "dehis¬ cence" of the posterior wall of the left frontal sinus. A computed tomographic scan showed a "soft-tissue mass" in the left frontal, ethmoid, and maxillary sinuses. She underwent a left-sided Caldwell-Luc procedure with nasal antrostomy, "polypectomy," left ethmoidectomy, and left frontal sinus trephination. Profuse bleeding was encountered during the ethmoidectomy. Pathologic

evaluation of the excised tissue revealed the presence of neural tissue thought to be of ectopie origin. Following removal of her upper nasal packing, the patient had a second seizure and was referred to our institution. After the initial examination, she underwent a sinus CT and an MRI and was found to have a left frontal meningoencephalocele that obstructed the left maxillary sinus ostium and hiatus semilunaris, apparently resulting in the finding of left-sided ethmoid and maxillary sinusitis. She subsequently underwent frontal craniotomy, excision of the meningoencephalocele, and repair of the frontal sinus and cribriform plate bony defect. The patient re¬ covered uneventfully. Case 3.—A 50-year-old white woman was seen initially for complaints of facial pain and nasal congestion. A facial CT scan revealed opacification of the right posterior ethmoid sinuses; a transnasal ethmoidectomy was performed. Over the next 2 years, she suffered from recurrent meningitis (treated with oral antibi¬ otics), chronic watery rhinorrhea, and severe frontal headaches with retro-orbital pain radiating to the left ear. She also reported some short-term memory loss and disequilibrium over this same time period. She was referred to our institution for further eval¬ uation and care. On endoscopie examination, a pulsatile mass was seen in the right posterior ethmoid air cell. On review of the CT scan, there was a suspicion of a bony defect in the posterior table of that same ethmoid air cell. An MRI was performed and revealed a menin¬ goencephalocele that extended into the right posterior ethmoid air cell. An intranasal endoscopie ablation of the meningoenceph¬ alocele and repair of the bony defect was performed. Her postop¬ erative course remains uneventful. Case 4.—A 40-year-old man with a remote history of a nasal fracture complained of chronic left nasal obstruction and facial pressure. An MRI of the head performed in an another institution revealed a large left-sided frontal meningioma. The patient underwent craniotomy and excision of a left-sided frontal men¬ ingioma. Postoperatively, the patient developed cerebropsinal fluid rhinorrhea. A CT scan of the head and another CT scan of the paranasal sinuses revealed postsurgical changes and opacifi¬ cation of the left ethmoid sinuses and left frontal sinus. Nasal en¬ doscopy revealed a soft-tissue mass filling the left nasal cavity (Fig 1). The MRI showed a large meningoencephalocele extend¬ ing from the frontal lobe to the nasal floor. The patient underwent superior and endoscopie resection of the meningoencephalocele, which extended through the cribriform plate. The durai defect was closed and the anterior cranial fossa floor defect was repaired with a split calvarial bone graft. Postoperatively, the patient did well with symptom resolution and no further cerebrospinal fluid leak in 7 months of follow-up.

COMMENT

Clinical Considerations

Postoperative complications from sinus surgery include the creation of bony defects in the floor of the anterior cra¬ nial fossa, although the exact incidence of this complication Downloaded From: http://archotol.jamanetwork.com/ by a Western University User on 06/09/2015

is unknown. Of the four cases presented, cases 1 and 3 represent the surgical creation or enlargement of a preex¬ isting bony dehiscence of the floor of the cranial fossa. Suwanwela and Suwanwela5 divide anterior cranial fossa meningoencephaloceles into two broad categories: frontoethmoidal and basal. Frontoethmoidal meningoenceph¬ aloceles protrude between the frontal and ethmoidal bones and are further subdivided into nasofrontal, nasoethmoidal, and naso-orbital meningoencephaloceles, depending on their extracranial presentation. Basal meningoenceph¬ aloceles are divided into transethmoidal, sphenoethmoi¬ dal, transsphenoidal, and spheno-orbital meningoenceph¬ aloceles.5 None of the basal variety are as commonly associated with congenital facial anomalies, such as mi¬

crocephaly, anophthalmia/microphthalmia, or hydrocephalus, as are the frontal meningoencephaloceles.5"9 It is, therefore, possible that frontal lesions are diagnosed more frequently, and at an earlier age, because of the presence

of concomitant anomalies that may alert the clinician to the presence of possible intranasal pathologic findings. A recent article described a patient with an intrasphenoidal encephalocele who presented with an ipsilateral retro-orbital headache.10 In that case, the diagnosis was made at the time of transseptal sphenoidotomy. Resection of the encephalocele was performed as well as a success¬ ful extracranial repair of the durai defect. Patients with meningoencephalocele may present in a variety of ways. Any intranasal mass in an infant or child should prompt the physician to consider the diagnosis of meningo¬ encephalocele.711"12 If the mass escapes detection through infancy and childhood, frequent modes of presentation in the adolescent and adult population include recurrent meningitis, watery rhinorrhea, seizures, nasal obstruction, and anosmia. A variety of these symptoms were demon¬ strated in the cases presented. Symptoms of sinusitis are rare but were present in two of our patients. It is also ap¬ parent from the literature that the adolescent and adult populations present the greatest potential for missed diagnosis because the incidence of mucoceles increases with age and the specter of latent congenital malformation seems more remote.11-13"17 The majority of meningoencephaloceles are found in the spinal region, extending from the base of the occipital bone to the sacrum. Twenty-five percent occur in the sincipital cra¬ nium, with further localization in the frontal (15%) and basal (10%) areas. In the United States, the incidence of congenital intranasal meningoencephalocele is 1/16 000.16 The experi¬ ence drawn from our cases (cases 2 and 3) implies that the presence of an intranasal meningoencephalocele predis¬ poses the patient to the development of sinus disease, pre¬ sumably from mass effect resulting in occlusion of sinus os¬ tia. It seems logical, therefore, to suggest that the prevalence of this disease is significantly higher in the population of pa¬ tients who are referred to an otolaryngologist-head and neck surgeon for the diagnosis and treatment of presumed or ex¬ isting sinusitis. It is also important to note that the wide¬ spread use of endoscopie techniques for direct visualization of nasal pathology will necessitate familiarity with the clin¬ ical as well as the radiologie features of intranasal menin¬

goencephalocele.

The intranasal

meningoencephalocele is described clin¬ ically as a pulsatile, gray/blue, compressible, faintly trans¬ lucent mass.8-9-11"14-18-19 Mucoceles characteristically extend medially into the nasal cavity and the paranasal sinuses, whereas the intranasal meningoencephalocele more com-

Fig 2.—Computed tomogram (CT) and magnetic resonance image (MRI) of a large encephalocele. Top, Coronal CT image through the anterior ethmoid sinus reveals a wide bony dehiscence (arrow) involving the left cribriform plate. The soft-tissue mass (asterisk) in the anterior ethmoid sinus has the same density and is inseparable from the brain. Bottom, Sagittal ,-weighted MRI reveals the brain herniation (arrows) into the ethmoid.

monly shows no lateral wall attachment. The intranasal meningoencephalocele may demonstrate a positive Furstenberg sign, which consists of swelling of the mass on jug¬ ular vein compression. The nasal glioma, a heterotopic nest of neural tissue that has lost its intracranial communica¬ tion, may grossly and histologically resemble an intranasal meningoencephalocele. It is, however, not pulsatile, manifests a negative Furstenberg sign, and may be re¬ moved safely as if it were a mucocele.12-20-21

Radiographic Considerations The CT examination is successfully being used as an ad¬ junct to endoscopie sinus diagnosis.1"4-11 Computed tomog¬ raphy optimally demonstrates the ostiomeatal channels, closely correlates with the endoscopist's evaluation plane, and provides a perceptible display of the relationship be¬ tween the intracranial compartment, the fovea ethmoi-

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together are beneficial for an accurate display of bone ero¬

Radiographic Diagnostic Criteria for Meningoencephaloceles* Appearance on

Diagnosis Meningoencephalocele normal ethmoid

in

well as the soft-tissue characteristics. A proper di¬ agnosis is critical in planning the proper surgical approach and foremost in avoiding serious complications. Radiographic criteria for the diagnosis of meningoencephalocele are shown in the Table. sion

MRI

Brain herniating into ethmoid (optimally

on sagittal and coronal images) Focal obliteration of bone and CSF signal: on T,WI, signal>brain; on T2WI,

as

displayed

Meningoencephalocele with ethmoid inflammation

signal>brain neoplasm Meningoencephalocele with carcinoma signal>brain; T2WI neoplasm signal>brain; T2WI neoplasm (SCCA) signal < inflammation *MRI indicates magnetic resonance imaging; CSF, cerebrospinal fluid; SCCA, squamous cell carcinoma. Although the incidence of intranasal meningoencephalocele is low in the general population, the prevalence in the population with chronic sinusitis seen by otolaryngologists may prove to be significantly higher. T.WI

dales, and the ethmoid sinus. The advantage of CT lies in its ability to simultaneously display bone, soft tissue, and

Computed tomography thereby provides an of the regional anatomy. The major disad¬ display optimal

air densities.

vantage of CT is a limitation of soft-tissue resolution that

makes normal tissue indistinguishable from inflammatory or neoplastic tissue. Thus, the diagnosis of an intranasal meningoencephalocele cannot be made with certainty with CT. This diagnosis should be suspected, however, in the presence of a dehiscence within the cribriform plate or ethmoid roof, especially if this finding is associated with an expansile intranasal mass (Fig 2). Note that the latter description is not specific and may also describe an ethmoid mucocele or neoplasm. Even though the bone resolution provided by MRI is unsatisfactory, its soft-tissue resolution is superb. Of equal orthogonal significance is the ability of MRI to scanning in virtually any plane. A direct and unsegmented view of the brain, fovea ethmoidales, cribriform plate, and ethmoid sinus is critical in this setting. Thus, a Trweighted coronal and /or a sagittal MRI through the cribriform plate will optimally display brain herniation into the ethmoid sinuses and nasal cavity (Figs 1 and 2), helping to distin¬ guish between an isolated intranasal mass and a mass arising from the intracranial compartment and extending

provide

intranasally.

Furthermore, the application of T2-weighted MRI has proven useful in distinguishing between bacterial and fungal sinusitis, and, in most instances, between inflam¬ matory and neoplastic tissue. Finding an isolated soft-tissue mass adhering to the cribriform plate and fovea ethmoidales should raise sus¬ picion of an intranasal meningoencephalocele. In this set¬ ting, the differential diagnosis should include a menin¬ goencephalocele, mucocele, or neoplasm, and MRI alone may be sufficient to differentiate among these entities. Should the pathologic findings be more extensive, where a combination of inflammatory tissue, meningoencephalo¬ cele, and/or neoplasm may be present, CT and MRI

CONCLUSIONS

The diagnosis of intranasal meningoencephalocele has historically been challenging and should be considered when evaluating a patient with a mass in the roof of the nose or in the sinuses adjacent to the skull base. Computed tomography is an essential part of this evaluation but lacks satisfactory soft-tissue resolution to determine the correct diagnosis. Because of MRI's excellent soft-tissue resolution and direct multiplanar scanning capability, essential for

proper demonstration of the fovea ethmoidales and crib¬ riform plate, we advocate the use of MRI for the diagnosis of intranasal meningoencephalocele. Magnetic resonance imaging should be performed on any patient who demon¬ strates an intranasal mass associated with clinical signs suggestive of meningoencephalocele on physical exami¬ nation, a history of watery rhinorrhea, meningitis, or sei¬ zures, and /or CT evidence of a base of skull bony defect. References Zinreich Rosenbaum 1. Kennedy DW, SJ, AE, etal. Functional endoscopic sinus surgery: theory and diagnosis. Arch Otolaryngol. 1985;111:576-582. 2. Zinreich SJ, Kennedy DW, Rosenbaum AE, et al. Paranasal sinuses: CT imaging requirements for endoscopic surgery. Radiology. 1987;163:769\x=req-\

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