Recurrent Abducens Nerve Palsy Due to Hidden Clival Meningioma in Dorello's Canal.

Dear Editor,

The abducens nerve is frequently involved in various intracranial pathologies, but recurrent abducens nerve palsy is rare and it requires a careful evaluation for a structural lesion along its course from the brainstem to the orbit.12 Here we report a patient with stereotypical recurrent abducens nerve palsy with a 2-year history due to a small meningioma involving Dorello’s canal, which had not been detected in initial gadolinium-enhanced routine brain MRI.

A 57-year-old female with dyslipidemia presented with the sudden onset of painless horizontal diplopia. The patient reported worsening of diplopia while looking into the distance and to the right, but denied diurnal symptom fluctuation (Fig. 1A). In a neurological examination, abducting saccades were slow and showed limitation in the right eye, while other neurological findings were normal. Routine serological tests and screening for autoimmune disorders produced normal results, including for rheumatoid factor, antinuclear antibody, anti-ds-DNA antibody, antineutrophil cytoplasmic antibody, IgG4, and amyloidosis. Tests for acetylcholine receptor antibody and repetitive nerve stimulation also produced normal results. Initial gadolinium-enhanced MRI produced no abnormal findings along the course of the abducens nerve (Fig. 1B). With a presumed diagnosis of isolated abducens nerve palsy due to microvascular ischemia, the patient was administered oral antiplatelet and low-dose atorvastatin. The diplopia completely resolved 5 months later. However, 4 months thereafter diplopia appeared again but without other signs, including periorbital pain. An examination revealed that the range of right-eye abduction was restricted to approximately one-half, and the velocity of right-eye abduction was also slow within the possible range of motion. Serological tests for autoimmune disorders and myasthenia gravis were again unrevealing. She did not undergo MRI because the diplopia and the limitation of eye movement resolved within 1 month of taking 60 mg of oral corticosteroid daily for 1 week. She was subsequently followed up regularly in the outpatient clinic with antiplatelet and atorvastatin. She reported diplopia for the third time at 15 months after the second attack, at which time the examination findings were the same as before (Fig. 1C). Follow-up gadolinium MRI at a sectioning thickness at 1 mm disclosed a meningioma in the right retroclival area, especially infiltrating Dorello’s canal (Fig. 1D). The diplopia disappeared after gamma-knife radiosurgery along with oral corticosteroids for 3 weeks, and the saccadic velocity and range of right-eye motion were normalized.

Fig. 1

Clinical and radiological findings in the patient. A: Nine-gaze photography showing abduction limitation of the right eye during the first attack. B: Initial MRI findings were interpreted as normal, including in the clival area (circle). C: Nine-gaze photography showing abducting limitation of the right eye at the third attack. D: Follow-up MRI disclosed a small meningioma (1.0 cm) in the right retroclival area (circle).

Recurrent abducens nerve palsy requires attention due to the possibility of neoplasm, multiple sclerosis, vasculitic neuropathy, and recurrent painful ophthalmoplegic neuropathy rather than simply microvascular ischemia.123456 A previous study found that the most common etiology of recurrent isolated abducens nerve palsy was neoplasm (4/7, 57%), predominantly meningioma (3/4, 75%).1 In addition, ocular myasthenia and thyroid eye disease may mimic recurrent abducens nerve palsy.7 The exact pathomechanism of the recurrent abducens nerve palsy in tumorous lesions has been unclear. In the present case, hidden clival meningioma was missed in the initial MRI. Furthermore, the clinical manifestation was episodic and stereotypical rather than progressive or chronic, as typically observed in neoplastic lesions. Therefore, as it slowly enlarged, the meningioma in our patient appears to have compressed the dorsal clival or meningeal artery, a branch of the meningohypophyseal trunk supplying the proximal segment of the intracranial abducens nerve, rather than directly compressing the nerve, thereby creating a cyclic ischemic demyelinating neuropathy.8 In conclusion, recurrent abducens nerve palsy requires a careful evaluation for a structural lesion along its course using gadolinium-enhanced thin-section MRI.