140 Surg Neurol 1988;30:140-3 Giant Peripheral Aneurysm of the Posterior Inferior Cerebellar Artery Treated with Excision and End-to-End Anastomosis Joseph R. Madsen, M.D., and Roberto C. Heros, M.D. Neurosurgery Science, Massachusetts General Hospital, Boston, Massachusetts Madsen JR, Heros RC. Giant peripheral aneurysm of the posterior inferior cerebellar artery treated with excision and end-to-end anastomosis. Surg Neurol 1988;30:140-3. A patient with a giant aneurysm arising from the tonsillomeduUary segment of the posterior inferior cerebellar artery (PICA) presented with clinical and computed tomography findings suggestive of spontaneous cerebellar hemorrhage. Magnetic resonance imaging led to arteriography and the correct diagnosis. Lack of a clippable neck on the aneurysm and its location proximal to the choroidal point prompted treatment by excision of the aneurysm and end-to-end anastomosis of the PICA. No neurological deficit resulted from the procedure. KEY WORDS: Posterior inferior cerebellar artery; Giant aneurysm; Magnetic resonance imaging Aneurysms arising from the posterior inferior cerebellar artery (PICA) are uncommon, accounting for only 0 . 5 % - 3 % o f all intracerebral aneurysms [4,7,8,10-14]. Giant (>2.5 cm) aneurysms of the PICA are so rare that Drake's large series o f giant aneurysms included no cases [3]. Only six giant aneurysms of any part o f the PICA had been reported in the English literature as o f a 1984 review, to which three recent cases from Japan have been added [5,9]. Most PICA aneurysms arise at the origin o f the vessel from the vertebral artery. Peripheral PICA aneurysms, regardless o f size, are also very rare; in a recent review, we found only 61 cases in the English literature [1]. We report the case o f a patient with a giant peripheral aneurysm of the PICA whose clinical presentation and computed tomography (CT) scan suggested the diagnosis o f a subacute cerebellar hemorrhage. Had it not been for the findings on magnetic resonance imaging (MRI), which Address reprint requests to: Dr. Roberto C. Heros, Director of Cerebrovascular Surgery, Massachusetts General Hospital, Boston, Massachusetts 02114. Received April 23, 1987; accepted August 3, 1987. © 1988 by Elsevier Science Publishing Co., Inc. led to arteriography and the correct diagnosis, the patient would have been treated conservatively and remained at risk from recurrent aneurysmal hemorrhage or enlargement. Case Report A 65-year-old Colombian man, otherwise well except for moderate hypertension treated with beta-blockers, awoke one morning with headache, nausea, dizziness, and ataxia. H e noted particular difficulty with gait and collided with objects when trying to walk. The nausea and headache improved spontaneously but the dizziness and ataxia remained constant. A C T scan obtained in Colombia 2 months after the onset of symptoms demonstrated a large, central cerebellar, hyperdense lesion (Figure 1). T h e r e was minimal contrast enhancement at the edge of the lesion, which was interpreted as being a tumor or a hemorrhage within a tumor. Screening tests for metastatic disease, including chest x-ray, intravenous pyelography, and bone scan, were all negative. H e was referred to the Massachusetts General Hospital ( M G H ) with a diagnosis of probable cerebellar tumor. Admission neurological examination at M G H found him alert and fluent in speech. Fine nystagmus was present on full right gaze, and the extraocular movements were otherwise normal. Lower cranial nerve function was intact. Strength was normal, but dysmetria and fine m o t o r impairment were present, more in the right arm than the left. Significant truncal ataxia prevented him from being able to walk without a cane. The reflexes and plantar responses were normal. Our initial diagnosis was spontaneous hypertensive cerebellar hemorrhage, but because the lesion continued to appear as a high density lesion on a CT scan done 2 months after onset o f symptoms, we obtained a magnetic resonance image to rule out underlying pathology. This study demonstrated areas of strikingly inhomogeneous signal density, particularly on the T2weighted study, which were interpreted as being consistent with thrombosis or hemorrhage of different ages within the abnormal region (Figure 2). Suspicion of 0090-3019/88/$3.50 Giant Peripheral PICA Aneurysm A Surg Neurol 1988;30:140-3 141 B Figure 1. CT scan taken 2 months after the onset of symptoms, showing an irregular hyperdense region in the cerebellum (A), with enhancement after intravenous contrast material (B). multiple hemorrhages led to angiography, which disclosed a small, bilobed, peripheral PICA aneurysm (Figure 3). W e surmised that the aneurysm had bled on more than one occasion into the cerebellar parenchyma, thus accounting for the MRI findings. Figure 2. T~-weighted magnetic resonance image of the posterior fossa, showing regions of variable density consistent with thrombosed blood of different ages. Figure 3. Cerebral angiogram obtained after injection of the right vertebral artery, demonstrating a peripheral bilobedaneurysm of the PICA. 142 Surg Neurol 1988;30:140-3 Madsen and Heros GIANT ANEURYSM BETWEEN CEREBELLAR PICA WITH PERFORATORS ANTERIOR TO ANEURYSM \ \ Figure 4. Artist's drawing of the operative field. EXTENT OF GIANT ANEURYSM (thrombosed) PICA / / / / l/ ~'~ ' ~ - ~ iI PICA PATENT BILOBED REGION WITHIN THROMBOSED AREA The aneurysm was approached through a wide suboccipital craniectomy, with removal of the posterior arch of C-1. To our surprise we encountered a giant (3.2 cm) aneurysm between the cerebellar tonsils immediately upon opening the dura mater. The aneurysm projected upwards between the tonsils toward the fourth ventricle. It was mostly thrombosed, except for two regions of patency near the neck, which corresponded to the two "lobes" visualized on the angiogram (Figure 4). There was evidence of some parenchymal hemorrhage around the aneurysm, but most of the clot was intraaneurysmal. The PICA was followed proximally to the vertebral artery, revealing that the aneurysm arose on the tonsiUomedullary segment, prior to the origin of important perforating vessels to the brain stem and deep cerebellar nuclei [3,6]. To avoid sacrificing the artery, proximal and distal temporary clips were placed, and the bulk of the aneurysm was excised. Aneurysmorrhaphy was performed on the remaining cuff after removal of all thrombus. On releasing the temporary clips, however, there was no flow through the lumen. We attributed this to probable injury to the intima at the orifices of entrance and exit during aneurysmorrhaphy. To restore flow, the clips were reapplied, and the cuff of the aneurysm was excised. The artery was then anastomosed in an end-to-end fashion. Back and front anchoring stitches of 10-0 nylon were placed, and then the anastomosis was completed with four or five interrupted sutures on each side. Robust pulsatile flow was evident on releasing the clips. Postoperatively the patient noted improvement in gait and there was no new deficit. He left the hospital on the fourth postoperative day. In view of the clinical improvement and cost considerations, we did not feel that postoperative angiography was indicated. Giant Peripheral PICA Aneurysm Discussion This patient's clinical presentation with abrupt development o f ataxia, dizziness, and headache was typical for a spontaneous cerebellar hemorrhage. The symptoms did not progress over the 2-month period prior to his transfer to our hospital. To rule out underlying pathology, such as a tumor which had bled, we obtained a magnetic resonance image. This study suggested blood clot and/or hemorrhage o f different ages. Without this MRI finding we would not have proceeded with arteriography or surgery, in view of the stability of the patient's symptoms. However, given evidence of probable multiple hemorrhages (which turned out to be a combination o f thrombus within the giant aneurysm and a small surrounding parenchymal hemorrhage), arteriography was warranted. Thus, MRI significantly altered diagnostic and therapeutic considerations in this case. Given the operative findings, available surgical options included (1) clipping the neck o f the aneurysm, (2) ligating the P I C A proximal to the aneurysm, and (3) performing aneurysmorrhaphy to remove the bulk of the lesion and preserve P I C A flow. The first and generally preferable option was not technically feasible because o f the lack o f a definable neck, resulting from the fusiform base o f the aneurysm, and the large amount o f mural thrombus. Ligation of the PICA can be safely used for more distally located aneurysms but is potentially dangerous with aneurysms located proximal to the choroidal point because important branches to the brain stem and deep cerebellar nuclei are located before this point [1,4,6]. In this case, aneurysmorrhaphy was attempted, but it was technically unsatisfactory. This prompted us to proceed with aneursymal resection and end-to-end anastomosis, a maneuver previously used by Dolenc [2] to treat a patient with a fusiform aneurysm of the PICA. Because o f the lack o f postoperative angiography, we cannot claim postoperative patency of the anastomosis, in spite o f its apparent normal flow at the conclusion of the operation. Conclusion Giant peripheral P I C A aneurysms can present as cerebellar parenchymal lesions. MRI can be an important Surg Neurol 1988;30:140-3 143 diagnostic aid and should be considered in cases of apparent spontaneous cerebellar hemorrhage with unusual clinical or CT features. Aneurysmal resection with end-to-end anastomosis o f the P I C A is a surgical option to be considered in cases of peripheral giant PICA aneurysms. References 1. Beyerl DB, Heros RC. Multiple peripheral aneurysms of the posterior inferior cerebellar artery. Neurosurgery 1986;19: 285-9. 2. Dolenc V. End-to-end suture of the posterior inferior cerebeUar artery after the excision of a large aneurysm: case report. Neurosurgery 1982;11:690-3. 3. Drake CG. Giant intracranial aneurysms:experience with surgical treatment in 174 patients. Clin Neurosurg 1979;26:12-95. 4. Hudgins RJ, Day AL, Quisling RG, Rhoton AL Jr, Sypert GW, Garcia-Bengochea F. Aneurysms of the posterior inferior cerebellar artery. 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