Keywords
trochlear nerve - meningioma - nerve infiltration - neuropathology
Introduction
Tumors of the trochlear nerve are rare; even schwannomas, the most common pathology,
comprise only ∼30 cases in the literature.[1]
[2] Other pathologies include meningioma especially of the cavernous sinus,[3] hemangioblastoma,[4] cavernous angioma,[5] and neurofibroma.[6] Here we present an isolated trochlear nerve meningioma demonstrating infiltration
of the tumor into the nerve tissue, which represents the first case of its kind to
be reported. A brief review of cases in which meningioma infiltrated cranial nerves
and the implications for tumor grading are discussed.
Case Report
A 52-year-old male with no medical history presented with blurred and double vision.
He first developed dizziness and blurred vision 10 years prior during a soccer game.
From that point, he noticed mild double vision with physical exertion. As the diplopia
progressed, he started wearing prism glasses 5 years ago but still had symptoms when
fatigued. He underwent left inferior rectus recession surgery and had resolution for
∼1 year, but his double vision eventually returned. At presentation, he wore nonprescription
prism glasses that resolved the diplopia but required replacement with stronger prisms
every year. On physical exam, he demonstrated a mild, intermittent head tilt to the
right. No obvious restriction of his extraocular movements was noted, but the patient
reported worsening diplopia on right inferior gaze. Contrast-enhanced magnetic resonance
imaging scan of the brain showed a 4 mm enhancing mass along the left ventrolateral
pons in the area of the trochlear nerve, extra-axial but not dural-based.
The differential diagnosis included schwannoma, which was considered the likelier
pathology, or meningioma, and the options of observation versus surgical removal were
discussed. The progression of his diplopia suggested ongoing nerve damage caused either
by compression or infiltration of the trochlear nerve. The options for observation
or surgical intervention were discussed, and the patient elected to have surgery for
diagnosis as well as surgical cure. The patient underwent a preauricular middle fossa
craniotomy for resection of the mass. The trochlear nerve appeared to insert directly
into the tumor, clinically more suggestive of a schwannoma. The proximal trochlear
nerve was then sharply divided and the tumor was removed.
Pathological study demonstrated a meningiothelial meningioma (WHO Grade I) with no
atypical histological features ([Fig. 1]). The tumor was focally positive for EMA, but negative for progesterone receptors.
The overall K
i-67 proliferation index was 3% to 4%. A neurofilament stain demonstrated invasion
by the meningioma into a peripheral nerve segment ([Fig. 2]).
Fig. 1 Hematoxylin and eosin stain showing loose whorls and syncytia consistent with a meningothelial
meningioma.
Fig. 2 Neurofilament immunostain showing invasion of tumor into peripheral nerve tissue.
Discussion
There are two prior cases in the literature of meningioma invading the trochlear nerve.
The first case[7] was described in a patient with von Recklinghausen's disease, who had fusiform mass
of the right trochlear nerve found incidentally during resection of a right cerebellopontine
angle. The mass was resected and pathological study demonstrated a meningothelial
meningioma with nerve fibers found in the periphery. The second case[3] involved a cavernous sinus meningioma that had encased the right trochlear nerve.
The nerve was resected, and pathological study demonstrated infiltration by a syncytial
meningioma.
Conclusion
Nerve infiltration is not a criterion used in grading meningiomas,[8] likely due to the rarity of cases and the lack of follow-up that would demonstrate
that this feature is a risk factor for recurrence. Reports of nerve infiltration by
meningioma include three cases of optic nerve invasion by optic nerve sheath tubular–diffuse
type meningiomas;[9] two cases of optic nerve invasion by intraorbital meningiomas, one transitional
type found on autopsy and the other angiomatous type that was disease-free 28 years
after resection;[10] trigeminal (V3) nerve invasion by a syncytial meningioma;[3] and accessory nerve invasion[11] by a meningothelial type meningioma. While one case series of jugular foramen meningiomas
reports that these tumors commonly invade the lower cranial nerves,[12] there is limited evidence of this behavior to be found in the literature.
