Caught Between the Brain and a Hard Place: A Case of a Cervicomedullary AVM.

Posterior fossa arteriovenous malformations (AVMs) are uncommon lesions that carry significant risk due to their proximity to the brainstem. We present the case of an 18-year-old female who suffered a sudden severe headache and was found to have a subarachnoid haemorrhage caused by a cervicomedullary junction AVM of the juvenile Type IIa subtype. Multimodality imaging with noncontrast CT, MRI and digital subtraction angiography (DSA) confirmed a posterior fossa AVM centred at the cervicomedullary junction. The patient was managed conservatively with strict blood pressure control and analgesia; Gamma Knife radiosurgery was considered but deferred given the diffuse nidus and the lesion's location adjacent to the medulla. This case illustrates the diagnostic and therapeutic challenges of posterior fossa AVMs in young patients and highlights the crucial role of multimodality imaging in guiding management decisions.