Partial oculomotor nerve palsy in a 7-year-old child.

Oculomotor nerve palsy can be due to varied causes that include diabetic neuropathy, myasthenia gravis, brainstem infarction, demyelinating conditions, and cerebral aneurysms. Among the aneurysmal causes of oculomotor nerve palsy, aneurysm of the posterior communicating artery has been observed to be the most common. Pupillary dysfunction is considered to be an important feature of aneurysmal oculomotor nerve paresis. A case of a 7-year-old boy with partial oculomotor nerve palsy with pupillary sparing is being reported here, the etiology of which is tortuous and ectatic distal internal carotid artery. This is a rare cause of oculomotor nerve paresis and to the best of our knowledge has not yet been reported in children. Ischemia rather than compression seems to be the most plausible cause in this case.

Introduction

Oculomotor nerve palsy secondary to posterior cerebral artery (PCA) aneurysm is common. However, tortuous and ectatic distal ICA may rarely cause oculomotor nerve palsy due to impairment of blood supply to oculomotor nerve rather than by direct mechanical compression.[12]

Case Report

A 7-year-old male child presented with sudden onset droopy eyelids and painless limitation of upward movement of the right eye for the last 2 days. There was no history of diurnal fluctuation of symptoms. There was no altered sensorium, seizures, any other apparent cranial neuropathy, flaccidity or tightness of limbs, paucity of limb movements, involuntary movements, jerky eye movements, swaying while walking, sensory complaints, or bowel bladder disturbances. There was no preceding febrile illness, trauma, prodromal illness, recent vaccination, animal bite, or drug intake.

Vital parameters were normal. General physical examination was unremarkable. Salient findings on neurological examination were ptosis and limitation of upward gaze in the right eye. Both pupils measured 3.5 mm with a normal reaction to light and accommodation. Fundus examination was normal. There was no other cranial nerve deficit. Motor, sensory, and cerebellar examination were normal. No cranial, cervical, or orbital bruit was audible. Other systemic examination was normal.

Routine hematological and biochemical investigations were normal. Magnetic resonance (MR) imaging brain revealed an abnormally large flow void in the region corresponding to the distal right internal carotid artery (ICA) with no infarct seen on diffusion weighted imaging. MR angiography showed tortuous and ectatic distal right ICA with marked attenuation of the right middle cerebral artery (MCA) and right anterior cerebral artery (ACA) [Figures 1a–c, 2a and b].

Figure 1

(a-c) Serial axial T2 weighted magnetic resonance images show a tortuous loop of right distal internal carotid artery with mild dilatation (arrows)

Figure 2

(a and b) Magnetic resonance angiography images show clearly the tortuous loop of the right distal internal carotid artery (long arrows). Note the highly attenuated right middle cerebral artery (dashed arrows)

Discussion

History and clinical examination in the current case localized the lesion to the superior division of right oculomotor nerve with neuroimaging showing ectatic and tortuous distal right ICA. As the pupillary fibers of the oculomotor nerve are located dorsally and peripherally, aneurysmal compression seems unlikely in the current case because of pupillary sparing and ischemic neuropathy appears to be the most likely cause.[12]

Ectatic right distal ICA leading to oculomotor palsy is rare and has not yet been reported in children. In a series of 84 patients with ICA-PCA aneurysms, 7 patients had pupillary sparing oculomotor nerve paresis among the 51 patients presenting with oculomotor nerve paresis.[1]

The ICA lies in proximity to the oculomotor nerve only within the cavernous sinus. Subarachnoid space is the most likely site of involvement in isolated III nerve palsies as opposed to cavernous sinus wherein accompanying trochlear and abducens palsy are also seen. Blood supply of oculomotor nerve from the ICA has several anatomical variations. It receives blood supply commonly from the nutrient arterioles (which usually arise from the branches of meningohypophyseal trunk and inferior cavernous artery) and perforating arteries, both arising from the ICA.[2] These branches may be prone to embolic, hemodynamic, or both mechanisms of ischemia.[123] Marked attenuation of branches of right ICA, namely, right MCA and ACA in the current case reiterates the fact that ischemia is the plausible mechanism, which has been reported previously.[45]

Conclusion

Thus abnormally dilated and or ectatic distal ICA rather than an aneurysm should be considered in cases of isolated oculomotor nerve palsy with pupillary sparing. Impaired blood supply to the oculomotor nerve is the most likely mechanism responsible rather than direct anatomical compression.

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Conflicts of interest

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