Ruptured cerebral arteriovenous malformation associated with enlarged parietal foramina: a rare surgical case with pathogenetic implications.

Enlarged parietal foramina (EPF) are rare, bilateral, symmetric calvarial defects, most commonly inherited in an autosomal-dominant manner. We report an exceptionally rare case of a ruptured parietal arteriovenous malformation (AVM) situated immediately beneath an EPF and resected via the calvarial defect. A 46-year-old man with no prior medical history presented with acute left upper-limb incoordination. Head computed tomography revealed a 3-cm right parietal subcortical hemorrhage and bilateral symmetric parietal defects; similar defects in his mother, uncle, and grandfather supported a diagnosis of familial EPF. The hemorrhage was directly subjacent to the defect, without antecedent trauma. Angiography identified a Spetzler-Martin grade I AVM within the hematoma. Using the EPF as a corridor, microsurgical resection was performed. The osseous defect was filled with fibrous connective tissue, and the dura was focally thickened with firm dural-arachnoid adhesions. The AVM nidus was removed en bloc. Postoperatively, left upper-limb incoordination resolved promptly and the patient was discharged with a modified Rankin Scale score of 0. Histopathology confirmed an AVM nidus and demonstrated infiltration of inflammatory cells, including polymorphonuclear leukocytes, around abnormal vascular walls and within the dura. Whole-genome sequencing revealed a pathogenic ALX4 nonsense variant (c.793C>T, p.Arg265Ter) and no pathogenic variants in established brain-AVM predisposition genes. The spatial concordance of EPF and AVM, together with the inflammatory histopathology, raises the possibility that EPF-associated inflammation may influence subjacent AVM biology or rupture susceptibility, although causality remains unproven.