Pupil-sparing third nerve palsy with preoperative improvement from a posterior communicating artery aneurysm.
BACKGROUND
Despite the plenitude of reports concerning partial or complete third nerve palsies, especially as presenting symptoms with posterior communicating artery (PCoA) aneurysms, we present a patient with an unusual variation.


METHODS
A 66-year-old woman presented with progressive right-sided headaches and diplopia and was found to have a partial, pupil-sparing third nerve palsy. A small right-sided PCoA aneurysm, nearly indistinguishable from an infundibulum, was identified on magnetic resonance angiography and subsequent digital subtraction angiography. The third nerve palsy improved before surgical repair of the aneurysm.


RESULTS
Microsurgical exploration revealed a small PCoA aneurysm, which was tethered to the third nerve by arachnoid adhesions. Adhesions were lysed and the aneurysm was repaired sparing the PCoA and its branches. The patient's third nerve function recovered completely postoperatively.


CONCLUSIONS
Even a very small PCoA aneurysm may present with an improving, pupil-sparing partial third nerve palsy. Selection of patients for imaging studies should take this unusual variant into consideration. We describe the anatomy and potential mechanisms of this pupil-sparing third nerve palsy.
Arle
Jeffrey E
JE
Department of Neurosurgery, Lahey Clinic, Burlington, Massachusetts, USA.
Abrahams
John M
JM
Zager
Eric L
EL
Taylor
Carolyn
C
Galetta
Steven L
SL
D000368:Aged; D015901:Angiography, Digital Subtraction; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000150:complications* / Q000000981:diagnostic imaging / Q000601:surgery*; D007498:Iris / Q000000981:diagnostic imaging*; D018810:Magnetic Resonance Angiography; D015840:Oculomotor Nerve Diseases / Q000000981:diagnostic imaging / Q000209:etiology* / Q000601:surgery*; D011300:Preoperative Care; D012075:Remission, Spontaneous