MR imaging of oculomotor nerve neurilemmoma

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Case Report MR IMAGING OF OCULOMOTOR NERVE NEURILEMMOMA TSUYOSHI KADOTA , * YOUJI MIYAWAKI ,T HIDEMITSU NAKAGAWA, t SINGO ISHIGURO,$ AND CHIKAZUMI KURODA* Departments of *Diagnostic Radiology, tNeurosurgery, and $Pathology, The Center for Adult Diseases, 3 Nakamichi 1-chome, Higashinari-ku, Osaka 537, Japan The authors present a proved case of neurilemmoma arising from the oculomotor nerve in which MR imaging, including enhancement by gadopentetate dimeglumine, dynamic study and three-dimensional gradient echo images, provided much more precise definition of the tumor. Keywords: Neurilemmoma; Oculomotor nerve; MRI.

right parasellar region (Fig. lA,B). Four vessel studies did not contribute to the diagnosis of the lesion. MR examination was performed on a 1.5-T imager (Siemens, Erlangen, Germany) with a circularly polarized head coil. Tr -weighted (500/15/2) (TR/TE/NEX) and Tz-weighted (3000/90/l) images were obtained in the axial plane. Enhanced Ti-weighted MR scans were performed in the axial plane, and in the coronal plane after the intravenous administration of gadopentetate dimeglumine at a dosage of 0.1 mmol/kg. All the spinecho (SE) images were acquired with the following parameters: section thickness of 5 mm; intersection gap of 1 mm; matrix size of 256 x 256. A well-circumscribed mass lesion of 2 cm in diameter was delineated in the right side of the suprasellar cistern. The tumor was found to be slightly hypointense relative to white matter on 7’,-weighted images (Fig. 1C). T,-weighted images revealed it as an isointense mass lesion (Fig. 1D). Dynamic MR study was performed by using short TR SE sequences (250/15/l) and an intravenous (IV) bolus injection of gadopentetate dimeglumine at a dosage of 0.1 mmol/kg. Before and after the IV bolus injection of gadopentetate dimeglumine, an eightimage series was acquired during the total dynamic examination time of 570 s. The time to signal intensity curve of the lesion demonstrated a gradual increase in intensity over time (Fig. 1E). The tumor showed homogeneously marked. enhancement with the use of gadopentetate dimeglumine (Fig. 1F). Unenhanced and enhanced three-dimensional (3D) gradient echo (GE)

INTRODUCTION Intracranial neurilemmomas arise commonly from sensory nerves, such as the eighth and fifth cranial nerves. Neurilemmomas originating from the oculomotor nerve are extremely rare diseases.lm4 Previous reports of the appearance of the tumor on magnetic resonance have been infrequent. As far as we know, there was only one report relating to MR imaging of the histologically verified oculomotor nerve neurilemmoma.5 It described a peculiar case of the third cranial nerve neurilemmoma with posthemorrhagic cystic change based on a moderate magnetic field imager and without the use of gadopentetate dimeglumine. We present a proved case in which MR imaging based on an imager with a high magnetic field, including enhancement by gadopentetate dimeglumine, dynamic study, and threedimensional (3D) gradient echo (GE) images, provided much more precise definition of oculomotor nerve neurilemmoma. CASE REPORT A 4I-yr-old man presented himself in August of 1991 complaining chiefly of diplopia and right ptosis. On admission, his neurologic examination disclosed a right oculomotor palsy, including pupillary dilatation and light reflex impairment. Plain skull films were unremarkable. CT showed an oval shape of a slightly hyperdense lesion with homogeneous enhancement in the RECEIVED3/l/93;

Address correspondence to Tsuyoshi Kadota, MD, PhD.

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(B) Fig. 1. (A) Precontrast CT scan showing a slightly hyperdense lesion. (B) Postcontrast neous enhancement in the medial area of the right middle fossa.

(Cl

CT scan revealing a region of homoge-

WY

Fig. 1. (C) T, - and (D) Tz-weighted images. T,-weighted image reveals a slightly hypointense mass lesion in the right side of the suprasellar cistern. The tumor is found to be isointense relative to normal white matter on the Tz-weighted image.

MRI of oculomotor nerve neurilemmoma 0 T. KADOTA

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Fig. 1E. Time-intensity curve. Signal intensities are normalized to the precontrast normal white matter. After an intravenous bolus injection of gadopentetate dimeglumine, serial seven images are acquired during the total dynamic examination time of 570 s.

Fig. 1. (G) Unenhanced moderate heterogeneity.

and (H) enhanced

3D FLASH

03 Fig. 1F. The tumor shows homogeneously ment after intravenous administration dimeglumine.

images (40/7/40”/1/2.5

mm contiguous

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marked enhanceof gadopentetate

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FLASH (Fast Low Angle Shot) images (40/7/l /flip angle 40”/2.5 mm contiguous section/l6 partitions) revealed moderate heterogeneity which was not noted on SE images (Figs. IG,H). A right frontotemporal craniotomy was performed. A solid intradural extra-axial tumor, which was noticed to be continuous with the oculomotor nerve, was totally removed. Representative microscopic sections revealed characteristic elongated cell proliferation with partial palisading (Antoni A type) (Fig. 1I). The postoperative course was uneventful. DISCUSSION Neurilemmomas account for 8-lO(r/o of primary intracranial tumors6 Most neurilemmomas arise from sensory nerves, the acoustic nerve being the most commonly affected. However, neurilemmomas originating from the oculomotor nerve without evidence of neurofibromatosis are rare. The oculomotor nerve fiber arises from its nucleus in the midbrain tegmentum, passes ventrally, and leaves from the medial aspect of

Fig. 11. Histological

specimen

showing

the cerebral peduncle. It courses anteriorly in the interpeduncular cistern, running through the lateral wall of the cavernous sinus, and enters the orbit through the superior orbital fissure. The initial symptom of the oculomotor nerve neurilemmoma is a oculomotor palsy, including diplopia, ptosis and pupillary dilatation. MRI is now considered the diagnostic method of choice for the evaluation of patients with cranial nerve neurilemmoma. MRI findings of the large majority of neurilemmomas are hypointense or isointense on T, weighted images, and isointense or hyperintense on Tz-weighted images. 7-9Our case also showed this pattern of slightly hypointense on Ti-weighted images and isointense on Tz-weighted images. Differential diagnoses include meningiomas, metastatic tumors, pituitary adenomas, chordomas, craniopharyngiomas, and aneurysms. Differential diagnosis from meningiomas is of significance because of the same pattern of the morphology and signal intensity. With the use of dynamic MR imaging, we obtained a gradual increase pattern of the time-intensity curve

spindle-shaped

tumor cells (H&E,

x 120).

MRI of oculomotor

nerve neurilemmoma

of neurilemmoma, which was different from that of meningiomas of a gradual decrease after a steep increase in signal intensity we experienced in 18 patients with intracranial meningiomas. Dynamic MR studies have been reported to be helpful in differentiating neurilemmomas from meningiomas, because of the high contrast resolution inherent to MR imaging.” Three-dimensional FLASH images demonstrated soft tissue contents within the tumor more clearly than SE images. This improved visualization of the tissue is attributed to the superior signal-to-noise ratio of GE pulse sequences over SE pulse sequences. In FLASH images, only part of the longitudinal magnetization is converted to transverse signal reducing the recovery period required to achieve high signal-to-noise ratio, which makes it possible to obtain contiguous thin slices providing high quality tissue contrast. The MR characteristics of oculomotor nerve neurilemmomas including contrast enhancement, dynamic study and 3D GE images are useful in diagnosing the lesion in the cranial base. REFERENCES 1. Leunda, G.; Vaquero, J.; Cavezude, J.; Cabezudo, J.;

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2. Okamoto, S.; Handa, H.; Yamashita, J. Neurinoma of the oculomotor nerve. Surg. Neural. 24:275-278; 1985. 3. Takano, S.; Endo, M.; Miyasaka, Y.; Yada, K.; Ohwada, T.; Takagi, H. Neurinoma of the oculomotor nerve. Neuro. Med. Chir. 30:132-136; 1990. 4. Mehta, V.S.; Singh, R.V.P.; Misra, N.K.; Choudhary, C. Schwannoma of the oculomotor nerve. Br. J. Neurosurg. 4~69-72; 1990. 5. Katsumata, Y.; Maehara, T.; Noda, M.; Shirouzu, I. Neurinoma of the oculomotor nerve: CT and MRI Features. J. Comput. Assist. Tomogr. 14:658-666; 1990. 6. Russell, D.S.; Rubinstein, L.J. Pathology of Tumors of the Central Nervous System, 4th ed. London: Edward Arnold; 1977:~. 372. 7. Curati, W.L.; Graif, M.; Kingsley, D.P.E.; King, T.; Scholtz, C.L.; Steiner, R.E. MRI in acoustic neuroma: A review of 35 patients. Neuroradiology 28:208-214; 1986.

8. Mikahael, M.A.; Ciric, I.S.; Wolff, A.P. MR diagnosis of acoustic neuromas. J. Comput. Assist. Tomogr. 11: 232-235;

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9. Press, G.A.; Hesselink, J.R. MR imaging of cerebellopontine angle and internal acoustic auditory canal lesions at 1.5 T. AJNR 9:241-251; 1988. 10. Fujii, K.; Fujita, N.; Hirabuki, N.; Hashimoto, T.; Miura, T.; Kozuka, T. Neuromas and Meningiomas: Evaluation of early enhancement with dynamic MR imaging. AJNR

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