Aneurysm of the meningeal branch of the occipital artery connecting with the distal portion of the posteroinferior cerebellar artery by the dural fistula.

We describe a case involving a ruptured intradural aneurysm of the meningeal branch of the occipital artery arising from the external carotid artery and connecting with the caudal loop of the posteroinferior cerebellar artery (PICA) by the dural fistula. Angiography of the left external carotid artery showed a saccular aneurysm of the occipital artery, but the picture of the left vertebral artery was normal and no vascular pathology such as an aneurysm or a dural fistula was noticeable between the meningeal branch of the occipital artery and the PICA. The diagnosis was confirmed by three-dimensional reconstruction computed tomography (CT) angiography, magnetic resonance imaging and magnetic resonance angiography (MRA). In the knowledge, based on the radiological examinations, that the aneurysm was located intracranially below the tonsil, compressing the lateral surface of the medulla oblongata at the level of the foramen magnum, we decided to operate from the far-lateral suboccipital approach, without removing the arc of the C1. An aneurysm was visualised at the site of the connection of the caudal loop of the PICA and an anastomosis of the meningeal branch of the occipital artery. The aneurysm was successfully clipped and the vascular fistula was coagulated and dissected in the extradural section. To our knowledge, the case presented here is the first report of this kind of vascular pathology. Careful analysis of a cross-sectional CT angiogram, MRA and arteriography is necessary for the proper diagnosis of such atypical vascular pathology. In the study presented we focus our attention on the diversity of the PICA anatomy.