Horizontal Diplopia at Distance and Right Gaze

Kelly A. Malloy, OD; Jean Marie Pagani, OD

Disclosures

June 23, 2016

Case Diagnosis

In this case, the combination of cranial nerve VI palsy and involvement of the trigeminal nerve may at first suggest cavernous sinus involvement. However, owing to the involvement of sensory and motor distributions of V3, which do not travel in the cavernous sinus, the lesion could not be contained solely in the cavernous sinus.

The combination of V2 and V3 involvement helps to localize the lesion to the Meckel cave, which houses the trigeminal or gasserian ganglion and is posterolateral to the cavernous sinus. Coinvolvement of cranial nerve VI can occur by either perineural spread to the cavernous sinus or by expansion of the mass to compress cranial nerve VI as it pierces the dura on its way to the cavernous sinus.

Orbital apex involvement would demonstrate some abnormality of optic nerve function or proptosis. All aspects of the afferent visual system evaluation were intact in this case. In addition, the absence of proptosis and the negative forced duction test were inconsistent with orbital involvement.

A pontine lesion would include additional neurologic features, possibly including ipsilateral cranial nerve VII involvement or body weakness and numbness contralateral to the abduction deficit, depending on the size and extent of the lesion. In this case, the muscles of facial expression were not affected and there was no indication of contralateral weakness or numbness. Aside from right cranial nerve V and VI involvement, the neurologic examination was otherwise unremarkable.

Workup and Treatment Plan

Owing to the combination of cranial nerves involved, as well as atrophy of the muscles of mastication, we were highly suspicious of a mass lesion involving cranial nerves V2, V3, and VI. MRI of the brain and orbits with and without contrast was performed, with special attention to the cavernous sinus, Meckel cave, and skull base.

MRI showed a right parasellar mass with heterogeneous enhancement, measuring 11 × 26 × 14 mm and extending from the right petrous tip to a point just proximal to the right orbit (Figures 5 and 6). There was no encasement of the right internal carotid artery. The mass extended into the right foramen ovale and 1 cm distally but did not extend into the orbit. There was also atrophy of the right pterygoid muscles and the right masseter muscle. The differential diagnosis listed on the radiology report included a cranial nerve V schwannoma or meningioma.

The mass was compared with the MRI done 1 year ago, and although that MRI was reported to be normal, it was determined that the mass had indeed been present at that time. It was thought to not have significantly changed in size during the 1-year interval.

Figure 5. Right parasellar lesion with enhancement (red arrows).

Figure 6. Coronal MRI section. Red arrows indicate atrophy of the muscles of mastication (temporalis, masseter, and pterygoid) on the right side compared with the corresponding muscles on the left side.

Because of the MRI findings, a neurosurgical consultation was arranged.

Reevaluation of the MRI along with the patient's clinical presentation caused concern about alternate etiologies, including lymphoma and sarcoidosis. For this reason, the patient underwent additional workup and imaging studies, including a serum angiotensin-converting enzyme blood test, lumbar puncture with cerebrospinal fluid analysis and cytology, and chest CT; none identified an etiology. He underwent CT of the maxillofacial region to determine a possible route for biopsy.

Three months after his initial presentation, the patient underwent a debulking procedure with biopsy, involving a craniofacial approach to the anterior cranial fossa extradural with anterior ethmoidectomy and partial maxillectomy with partial resection of the neoplasm of the anterior cranial fossa extradural.

Pathologic examination demonstrated amyloid infiltration of the nerve itself—not a tumor as suspected. There were no definite inflammatory cells or malignant cells. However, an oncology consultation was obtained to identify whether there was a cause for the amyloid production, such as cancer. The oncologist found no apparent cause for the amyloid infiltration and referred the patient to an outside treatment and research program that specialized in amyloidosis.

Subsequent bone marrow biopsy showed no amyloid deposits. No evidence of systemic amyloidosis was found on plasma cell dyscrasia workup. It was thought that the mass was a localized amyloidoma, with no evidence of regrowth. Mass spectroscopy was planned to assess the subunit protein to determine whether there was any role for radiation therapy.

In the interim, the patient was prescribed gabapentin to be taken daily to help with nerve discomfort. It was recommended that he see a dentist every 6 months because he may not feel any problems on that side of his mouth. Prism glasses in the form of 10 base-out prism were prescribed to alleviate his diplopia; however, he preferred to turn his head to the right to alleviate the diplopia because he was not accustomed to wearing glasses.

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