Case report of a de novo brainstem arteriovenous malformation in an 18-year-old male and review of the literature.

De novo intracerebral arteriovenous malformations (AVMs) are exceedingly rare with only seven reported cases in the literature. Although generally considered congenital by nature, the lesions do not manifest themselves clinically until the third or fourth decades of life. However, with the advent of improved imaging modalities and more frequent surveillance, an increasing number of de novo cases are being found challenging the concept AVMs develop in the perinatal/antenatal period. Alternatively, this phenomenon could represent a distinct entity in which lesion development occurs after birth. A PubMed search of "de novo cerebral arteriovenous malformation" was performed in which seven reported cases were found. The mean age at diagnosis was 14.7 years with a mean follow-up imaging study of 5.8 years. Lesion location was supratentorial in all previously described cases. This case involves an 18-year-old male with congenital hydrocephalus and seizures diagnosed at 7 months of age. The patient underwent a ventriculoperitoneal shunt and was followed frequently by a neurologist. The last diagnostic imaging was an unremarkable MRI of the brain at age 12. Seven years later, the patient presented with an intracerebral hemorrhage. A CT angiogram demonstrated a large brainstem AVM with an intraparenchymal hemorrhage and intraventricular extension. This case is unique in that it is the first infratentorial de novo AVM. The congenital nature of AVMs is challenged with the increasingly described series of patients with previously documented normal radiographic imaging. This suggests there may be a subset of patients genetically predisposed to postnatal development of AVMs.