Isolated abducens nerve palsy associated with subarachnoid hemorrhage: a localizing sign of ruptured posterior inferior cerebellar artery aneurysms

Abstract

OBJECTIVE Compressive cranial nerve syndromes can be useful bedside clues to the diagnosis of an enlarging intracranial aneurysm and can also guide subsequent evaluation, as with an acute oculomotor nerve (cranial nerve [CN] III) palsy that is presumed to be a posterior communicating artery aneurysm and a surgical emergency until proven otherwise. The CN VI has a short cisternal segment from the pontomedullary sulcus to Dorello's canal, remote from most PICA aneurysms but in the hemodynamic pathway of a rupturing PICA aneurysm that projects toward Dorello's canal. The authors describe a cranial nerve syndrome for posterior inferior cerebellar artery (PICA) aneurysms that associates subarachnoid hemorrhage (SAH) and an isolated abducens nerve (CN VI) palsy. METHODS Clinical and radiological data from 106 surgical patients with PICA aneurysms (66 ruptured and 40 unruptured) were retrospectively reviewed. Data from a group of 174 patients with other aneurysmal SAH (aSAH) were analyzed in a similar manner to control for nonspecific effects of SAH. Univariate statistical analysis compared incidence and risk factors associated with CN VI palsy in subarachnoid hemorrhage. RESULTS Overall, 13 (4.6%) of 280 patients had CN VI palsy at presentation, and all of them had ruptured aneurysms (representing 13 [5.4%] of the 240 cases of ruptured aneurysms). CN VI palsies were observed in 12 patients with ruptured PICA aneurysms (12/66 [18.1%]) and 1 patient with other aSAH (1/174 [0.1%], p < 0.0001). PICA aneurysm location in ruptured aneurysms was an independent predictor for CN VI palsy on multivariate analysis (p = 0.001). PICA aneurysm size was not significantly different in patients with or without CN VI palsy (average size 4.4 mm and 5.2 mm, respectively). Within the PICA aneurysm cohort, modified Fisher grade (p = 0.011) and presence of a thick cisternal SAH (modified Fisher Grades 3 and 4) (p = 0.003) were predictors of CN VI palsy. In all patients with ruptured PICA aneurysms and CN VI palsy, dome projection and presumed direction of rupture were directed toward the ipsilateral and/or contralateral Dorello's canal, in agreement with laterality of the CN palsy. In patients with bilateral CN VI palsies, a medial projection with extensive subarachnoid blood was observed near bilateral canals. CONCLUSIONS This study establishes a localizing connection between an isolated CN VI palsy, SAH, and an underlying ruptured PICA aneurysm. CN VI palsy is an important clinical sign in aSAH and when present on initial clinical presentation may be assumed to be due to ruptured PICA aneurysms until proven otherwise. The deficit may be ipsilateral, contralateral, or bilateral and is determined by the direction of the aneurysm dome projection and extent of subarachnoid bleeding toward Dorello's canal, rather than by direct compression.

Intracranial aneurysms and abducent nerve palsy

“…[6] A range of aneurysms, including those affecting the PICA, ICA, Acom, posterior communicating artery, and middle cerebral artery aneurysms, hold the potential to impact the abducent nerve function. [1,3,5,10] According to the findings of our study, a noteworthy association has been established between the abducent nerve and ruptured PICA aneurysms. While, in the context of unruptured aneurysms, a statistically significant correlation has been identified between the abducent nerve palsy and factors such as the cavernous location, and dome size.…”

“…is aligns with the work of Burkhardt et al, who investigated 13 patients with 6 th nerve palsy from a broader cohort of 106 patients displaying PICA aneurysms. [1] e researchers suggest the abducent nerve palsy as a potential localizing sign for a ruptured PICA aneurysm. However, considering that the sample size could pose limitations to drawing definitive conclusions.…”

“…us, CN 6 th palsy can be linked to aneurysms originating from arteries with close anatomical proximity. [1] Existing literature reveals a paucity of studies addressing the involvement of the 6 th CN in cerebral aneurysms. Here, we share our experience with 6 th nerve palsy as a presenting feature for intracranial aneurysms, along with an analysis of associated aneurysmal characteristics and the CN's follow-up and functional outcome.…”

Clinical Importance of the Posterior Inferior Cerebellar Artery: A Review of the Literature

“…Although abducens nerve was not directly adjacent to PICA, ruptured PICA aneurysm could result in isolated abducens nerve palsy, which was possibly associated with the hemodynamics of aneurysmal rupture instead of direct compression 58 . Burkhardt et al demonstrated ruptured PICA aneurysm was an independent risk factor of abducens nerve palsy 59 . Giant aneurysms might be misdiagnosed as tumors of posterior fossa due to similar symptoms and imaging features which were sometimes indistinguishable even with magnetic resonance angiography (MRA) and digital subtraction angiography (DSA) 46 , 47 .…”

A Rare Case of Isolated Abducens Nerve Palsy With Contemporaneous Thalamic Infarct

“…Another case report underscores the importance of neuroimaging even in cases of isolated abducens nerve palsy, as CT angiography revealed a ruptured posterior inferior cerebellar artery (PICA) aneurysm and subarachnoid hemorrhage [ 13 ]. A retrospective study establishes a localizing relationship between isolated abducens nerve palsy, subarachnoid hemorrhage, and an underlying ruptured PICA aneurysm [ 14 ]. Hence, isolated abducens nerve palsy should not be overlooked, and appropriate neuroimaging should be considered.…”