Probable pathogenesis, diagnosis, and management of untreated arteriovenous malformation with cyst formation: case report and literature review.

Arteriovenous malformations (AVMs) usually manifest as headaches, seizures, focal neurological signs, and spontaneous intracerebral or subarachnoid hemorrhages. An untreated AVM with associated cyst formation is extremely rare, and the probable pathogenesis is unclear. We propose and discuss the possible pathogenesis of this condition and its diagnosis and management. A 26-year-old male presented with a generalized tonic-clonic seizure. Computed tomography showed a cystic lesion in the left frontal lobe and magnetic resonance imaging revealed a complex composition within the lesion, without a flow-voiding signal. Therefore, the initial diagnosis was oligodendroglioma and surgical treatment was performed. However, intraoperatively, engorged reddish nodule-like vessels with a cystic capsule and intra-cyst brown and sticky fluid were found. The nodule-like vessels and cystic capsule were resected completely. The patient's postoperative course was uneventful, with an excellent neurological outcome and no further seizures. Pathological examination of the surgical specimen revealed the typical microscopic appearance of an AVM, with numerous thin-walled vascular channels and deposits of hemosiderin in fibrous tissue. In conclusion, an untreated AVM with associated cyst formation is extremely rare, and the mechanism of formation is unclear. We propose a probable pathogenesis. Preoperative diagnosis, intraoperative management, and postoperative follow-up are equally crucial in dealing with this extremely rare condition. Cystic tumors associated with arteriovenous malformations (AVMs) are uncommon and are usually a complication of stereotactic radiosurgery (Ilyas et al. in J Neurosurg. https://doi.org/10.3171/2016.12.JNS162478 , 2017) or form after a hemorrhage (Daniels et al. in Radiology 133:393-394, 1979). Untreated AVMs with large cysts or cystic tumors are rare, with only five cases reported in the literature (Table 1). Here, we present a case of an untreated AVM associated with cystic formation, or a cystic tumor, in the left frontal lobe.