A Rare Case: Primary Venous Malformation in Parietal Bone.

Primary intraosseous vascular malformations (PIVMs) are rare intraosseous lesions, accounting for approximately 0.5-1% of all intraosseous tumours. In this case report, we aimed to present a rare case of intraosseous vascular malformation causing a large lytic area in the parietal bone. A 25-year-old male patient was admitted to the clinic with a mass on the parietal bone. On physical examination, it was observed that the hair density on the mass was decreased, the mass had a soft consistency, and there was no pain on palpation. The patient was operated under local anaesthesia with a provisional diagnosis of a trichilemmal cyst. However, intraoperative diagnosis was a vascular malformation. There was a 3-cm full-thickness defect on the parietal bone caused by the lesion. The mass was excised completely while preserving the integrity of the dura. The resulting defect was reconstructed with bilateral rotation advancement flaps. The calvarial defect was not reconstructed due to equipment inadequacy. No complications were encountered in the postoperative period. Ninety-three PIVM cases have been reported in the skull since 1845. In very few of these cases, the mass is located in the parietal bone. The pathogenesis of PIVMs is not completely understood. The definitive diagnosis is made by histopathological examination. The therapeutic gold standard is surgery. Surgeons should keep in mind that radiological examination before the operation could prevent undesirable complications.