Unilateral Trans-cerebellomedullary Fissure Approach for Occipital Artery to Posterior Inferior Cerebellar Artery Bypass during Aneurysmal Surgery

Abstract

Occipital artery (OA) to the posterior inferior cerebellar artery (PICA) bypass is indispensable for the management of complex aneurysms of the PICA that cannot be reconstructed with surgical clipping or coil embolization. Although OA-PICA bypass is a comparatively standard procedure, the bypass is difficult to perform in some cases because of the location and situation of the PICA. We describe the usefulness of the unilateral trans-cerebellomedullary fissure (CMF) approach for OA-PICA bypass. Thirty patients with aneurysms in the vertebral artery (VA) or PICA were treated using OA-PICA bypasses between 2010 and 2015. Among them, the unilateral trans-CMF approach was used for OA-PICA anastomosis in 13 patients. The surgical procedures performed on and the medical records of all the patients were retrospectively reviewed. The unilateral trans-CMF approach was performed for two reasons depending on the PICA location or situation: either because the caudal loop could not be used as a recipient artery because of arterial dissection (3 patients) or because the tonsillo-medullary segment that was located in the upper part of the CMF did not have a caudal loop that was large enough (10 patients). The trans-CMF approach provided a good operative field for the OA-PICA bypass and the anastomosis were successfully performed in all patients. When the recipient artery was located in the upper part of the CMF, the unilateral trans-cerebello-medullary fissure approach provided a sufficient operative field for OA-PICA anastomosis.

Keywords: bypass surgery; cerebellomedullary fissure; occipital artery; posterior inferior cerebellar artery; trans cerebellomedullary fissure approach.

Fig. 1

Radiological and intraoperative images of patient #2 (A) Left vertebral artery (VA) angiography revealed an aneurysm at the proximal portion of the posterior inferior cerebellar artery (PICA; asterisk). The pearl and string sign of the PICA can be seen at the lateral medullary segment. (B) The patient was placed with his right side down in a park-bench position, and a horseshoe shaped was made. The occipital artery (OA) was stripped from the skin-muscle flap (black arrow). A left lateral suboccipital craniotomy with drilling of the lateral part of the foramen magnum and condyle fossa were performed. (C) An aneurysm of the proximal portion of the PICA was observed (asterisk). The wall of the aneurysm was very thin. (D) The left cerebellomedullary fissure (CMF) was dissected as widely as possible in order to expose the cerebellomedullary space (white dotted line). The entire area of the lateral medullary segment and tonsillo-medullary segment of the PICA were discoloured purple by arterial dissection (black arrowheads). The normal coloured cranial loop of the telovelotonsillar segment was identified at the upper level of the cerebello-medullary space (white arrow). (E) An OA (black arrows)-PICA end-to-side anastomosis was done at the proximal portion of the telovelotonsillar segment of the PICA (white arrow). The aneurysm was trapped with a titanium clip, and the dissecting PICA was resected for pathological examination. (F) Postoperative angiography revealed good patency of the OA-PICA bypass.

Fig. 2

Radiological and intraoperative images of patient #3 (A) A computed tomography scan revealed a diffuse subarachnoid haemorrhage that was predominantly seen at the left cerebello-pontine angle. (B) Left VA angiography revealed an aneurysm arising from the proximal portion of the PICA (white arrow). The tonsillo-medullary segment was located at the upper part of the CMF without a large caudal loop (white arrow head). (C) A enhanced computed tomography scan revealed a tonsillomedullary segment located at upper part of the CMF (white arrow head) located at the same level of the choroid plexus of the lateral recess (black arrow head). (D) The tonsillo-medullary segment of the PICA (asterisk) was exposed and displaced rostrally following wide opening of the CMF. (E) An OA-PICA end-to-side anastomosis was done using rubber sheet at the upper part of the cerebellomedullary space (white arrow). (F) Postoperative three-dimensional computed tomography angiography revealed successful trapping of the aneurysm (black arrow) and good patency of the OA-PICA bypass (white arrow).

Fig. 3

Schematic illustrations showing the relationship between the CMF and the tonsillomedullary segment of the PICA. An aneurysm of the proximal portion of the PICA is located in front of the lower cranial nerves. (A, B) These illustrations show typical type of the caudal loop of the tonsillomedullary segment of the PICA. The caudal loop is located at the lower level of the caudal tip of the tonsil. (A) The OA-PICA bypass was performed without using the trans-CMF approach. (B) An aneurysm is trapped using titanium clips. The transcondylarfossa approach was suitable for trapping of the aneurysm. (C, D) These illustrations show high position of the caudal loop of the PICA. (C) The caudal loop of the tonsillomedullary segment of the PICA, which is located in the upper part of the CMF without a large caudal loop, was exposed after opening the CMF. (D) The OA-PICA bypass and trapping of the aneurysm were performed using the trans-CMF approach.

Fig. 4

A cadaveric specimen shows the anatomy of the PICA. The tonsillo-medullary segment and telovelo-tonsillar segment of the PICA were exposed after dissecting the left CMF. This specimen has a large caudal loop of the PICA that is located at the lower level of the tonsil. C.N. = cranial nerve