Isolated Cranial Nerve VI Palsy in Pituitary Apoplexy

Background Pituitary apoplexy is a potential endocrinologic and neurosurgical emergency with an incidence ranging from 1 to 26% in patients with pituitary adenomas. Clinical presentations range from headache, metabolic, or hemodynamic derangements to acute vision loss and other cranial nerve palsies. A small subset of patients, however, can present only with an isolated cranial nerve palsy. Cranial nerves II and III dysfunction are well documented in the scientific literature. Isolated cranial nerve VI palsy is rare, and failure of its recognition can delay the diagnosis of pituitary apoplexy.

Methods The PRISMA methodology for systematic reviews was used to guide this study. Relevant articles were sourced from PubMed using the search terms “pituitary apoplexy” and “abducens nerve” or “sixth cranial nerve” or “sixth nerve,” and narrowed following the PRISMA protocol. Nine articles were selected for this review and patient data were extracted for comparison to our own data.

Results Clinical information from eight patients were used for this study. The variables were age, sex, history of trauma, acuity of neurologic symptoms including cranial nerve VI dysfunction, presence of other nonfocal symptoms, imaging findings, endocrinologic abnormalities, time to surgical intervention, histopathology, and time to reversal of palsy. The mean age was 52 years. There was a slight male preponderance, though the dataset was not powered to measure significant statistical differences in gender. Time to OR ranged from 4 days to 4 weeks. The cranial nerve VI palsies were all acute, complete, seen in patients with nonfunctioning adenomas, and were reversible, regardless of time to decompression in all but one patient with posttraumatic pituitary apoplexy. The syndrome was initially misdiagnosed in two patients.

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Discussion Cranial nerve palsies caused by pituitary apoplexy have been well documented in the literature. Often, these tumors affect cranial nerve II by superior expansion and cranial nerve III by lateral extension of the tumor. It is rare to find isolated cranial nerve VI deficits. We collated a cohort of eight patients, two from our practice, who presented with this finding. We compared these eight patients with larger studies that included all types of ocular cranial nerve palsies and found similar mean age, male predilection, and clinical symptoms. The majority of patients had nonfunctioning adenomas.

In the literature, it is hypothesized that isolated cranial nerve VI palsy is caused by tumor extension into Dorello’s canal. We suggest a new mechanism after thorough analysis of our patients’ MR imaging. Cranial nerve VI lies inferior and lateral to the carotid artery in the cavernous sinus. A lateral and inferior herniation of the tumor can spare cranial nerve III, which lies at the level of the pituitary gland, and compress only cranial nerve VI, producing the isolated deficit.

Fig. 1 MRI T1 post-contrast and T2 sequences demonstrating right inferior and later extension of pituitary tumor.