To describe a rare case of acute paraparesis syndrome (APS) after a ruptured aneurysm of the azygos anterior cerebral artery (ACA).

The incidence of APS within 24 hours after subarachnoid hemorrhage is very rare. Additionally, the pathophysiology of this syndrome remains poorly defined. Nonetheless, the literature suggests it could emerge from a bilateral ACA vasospasm, acute hydrocephalus, or global cerebral edema and can be associated with poor clinical status. The azygos ACA is a rare variant whose unique anatomy intensifies the hemodynamic stress on the arterial wall, making aneurysm formation closely associated with this anomaly.

A 72-year-old man with a past medical history of hypertension presented to the hospital with the complaint of acute paraparesis after a thunderclap headache and transitory loss of consciousness. The physical exam showed paraparesis with brisk patellar and Achilles reflexes and a neutral response to bilateral plantar stimulation. No abnormalities were noticed on the cranial nerves, coordination, and sensory examination.

Routine laboratory studies were normal. Brain computed tomography revealed an acute punctate hemorrhage of an aneurysm located in the frontal interhemispheric fissure. Magnetic Resonance Imaging (MRI) of the spine was unremarkable. Brain MRI showed unspecific white matter abnormalities, and an MR angiography showed a 4.3 mm saccular aneurysm in the right ACA A3 segment in the bifurcation of an azygos ACA. The patient underwent coiling of the aneurysm and was able to walk unassisted nine weeks after the procedure.

Acute paraparesis syndrome is a rare manifestation of a ruptured anterior communicating artery or anterior cerebral artery aneurysm. Here, we present an atypical etiology of APS caused by a ruptured aneurysm of the azygos ACA. To the best of our knowledge, this is the first description of an APS after a ruptured aneurysm of the azygos ACA.