After PICA passes the lateral aspect of the medulla, it courses around the cerebellar tonsil, enters the cerebellomedullary fissure, and passes posterior to the lower half of the fourth ventricle roof. ( b) The right cerebellomedullary cistern below the right cerebellar tonsil. The posterior inferior cerebellar artery (PICA) arises from the vertebral artery near the inferior olive and passes posteriorly around the medulla oblongata. ( a) Anterior view of the left brainstem and cerebellum. Its terminal portion is accompanied by the greater occipital nerve (Figs. The mean diameter of OA is 2.01 mm at the level of the superior nuchal line, and the mean length of this segment is 81.9 mm. There, OA changes course and runs vertically upward, piercing the fascia connecting the cranial attachment of the trapezius and sternocleidomastoid muscles, and ascends in a tortuous course in the superficial fascia of the scalp, where it divides into numerous branches that reach as high as the vertex of the skull and anastomose with the posterior auricular artery and superficial temporal artery (STA). The mean diameter of OA is 2.05 mm at its exit from the digastric groove. It then ascends between the transverse process of the atlas and the mastoid process of the temporal bone, and passes horizontally backward, grooving the surface of the mastoid process, while covered by the sternocleidomastoid, splenius capitis, longissimus capitis, and digastric muscles and resting on the rectus capitis lateralis, obliquus capitis superior, and semispinalis capitis muscles. OA crosses the internal carotid artery, internal jugular vein, and CNs X and XI. Cranial nerve (CN) XII winds around this artery from behind forward. At its origin, OA is covered by the posterior belly of the digastric muscle and the stylohyoid muscles. OA arises from the posterior portion of the external carotid artery, opposite the external maxillary artery and near the lower margin of the posterior belly of the digastric muscle, and ends in the posterior portion of the scalp. Although the benefits of intracranial OA–PICA bypass surgery for vertebrobasilar insufficiency caused by atherosclerotic disease of the extracranial or intracranial vertebral artery (VA) remain unclear, cerebral revascularization of the posterior circulation is well established for the treatment of complex and giant intracranial aneurysms and tumors, especially when these lesions involve the major vessels of the posterior circulation. Since then, OA–PICA anastomosis has been important for cerebral revascularization in the posterior circulation. and Piepgras DG and Khodadad G reported additional experiences of this procedure. performed the first intracranial posterior circulation revascularization procedure for vertebrobasilar insufficiency in the form of an OA–PICA anastomosis in 1976. An occipital artery–posterior inferior cerebellar artery (OA–PICA) anastomosis is performed when PICA is sacrificed during the treatment of poor posterior circulation.

Pica artery surgery