-1 rue posterior communicating artery a a . a aneurvsm Akimura T, Abiko S, It0 H. True posterior communicating artery aneurysm. Acta Neurol Scand 1991: 84: 207-209. T. Akimura, S. Abiko, H. Ito Two rare cases of true posterior communicating artery aneurysm are reported. One case was a saccular aneurysm, which was successfully clipped. The other was a case of fusiform trapped aneurysm, and hemiparesis and oculomotor palsy appeared transiently after surgery. In general, this type of aneurysm is included in the category of internal carotid-posterior communicating aneurysm, although some special considerations are necessary in surgical treatment. Key words: cerebral aneurysm; posterior communicating artery; subarachnoid hemorrhage; oculomotor palsy Tatsuo Akimura, Department of Neurosurgery Yamaguchi University School of Medicine, 1 144 Kogushi, Ube City, Yamaguchi 755, Japan True posterior communicating artery aneurysms (PCoAAs) can be defined as aneurysms which arise from the posterior communicating artery itself and are attached to neither the internal carotid nor the posterior cerebral artery. They have been included in the category of carotid-posterior communicating aneurysm. However, some reports with special reference to true PCoAAs have been published (1, 3, 5, 6 , 8, 13). We experienced 2 cases of true PCoAA, both of which were treated successfully. In this paper, we describe some unique characteristics and surgical procedures of these aneurysms. Department of Neurosurgery, Yamaguchi University School of Medicine, Japan Accepted for publication March 1, 199 1 Case reports Case 1 - The patient, a 57-year-old housewife, suffered a sudden headache and vomiting on August 19, 1979. She was admitted to a local hospital and was referred to our institution 4 days later. Computerized tomography (CT) scan revealed a diffuse cisternal clot and hematoma of the left Sylvian fissure. Angiograms revealed a tortuous and conglomerated aneurysm of the left posterior communicating artery itself (Fig. lA,B). Operation - Eleven days after the onset of symp- Fig. 1. Case 1. AP(A) and lateral (B) left carotid angiogram demonstrates a tortuous and conglomerated aneurysm of the posterior communicating artery. Left anterior cerebral artery is absent. (C) Postoperative angiogram shows complete obliteration of the aneurysm and segmental spasm of C1 and M1 portion. 201 Akimura et al. toms, a left frontotemporal craniotomy was performed. The left A1 portion was hypogenetic and abnormally elongated and a tortuous posterior communicating artery was noted. The interpeduncular cistern was dissected between the optic nerve and the internal carotid artery. A multilobulated fusiform aneurysm was recognized in the distal portion of the posterior communicating artery. Neck clipping was impossible and the aneurysm was trapped with two clips. Postoperative course - The patient had been in a somnolent state with left oculomotor palsy, right hemiparesis and motor aphasia. Postoperative angiograms revealed segmental spasm of the C1 and M1 portion with the aneurysm completely obliterated (Fig. 1C). Fourteen days after the operation, clear consciousness returned, although right hemiparesis, mild nominal aphasia, and left oculomotor palsy remained. CT scan showed hemorrhagic infarction of the left caudate nucleus and the internal capsule. Subsequently, neurological symptoms were markedly improved, and she was discharged six months after the operation. Case 2 - The patient was a 45-year-old women who suffered sudden severe head ache and stupor on March 5, 1988. She was referred to our ward 2 h after onset of symptoms. On admission, she was stuporous and aphasic and CT scan showed a diffuse cisternal clot. Angiograms revealed an aneurysm of the left posterior communicating artery (Fig. 2A,B) and diffuse spasm of the right C1, A1 and M1. Operation - On the same day, left frontotemporal decompressive craniotomy was performed. After the exposure the left IC, a bridging vein was cut during temporal lobe retraction. The approach was lateral to the internal carotid artery and the aneurysm was recognized through the perforating arteries from posterior communicating artery and clipped. The oculomotor nerve adhered to the dome of the aneurysm. Postoperative course - The patient became alert 2 days after the operation, but on Day 8th, she became slightly disoriented due to symptomatic vasospasm. Postoperative angiograms showed successful clipping except for a minimal remnant of the dome of the aneurysm and diffuse spasm of the cortical branches of the left middle cerebral artery (Fig. 2C). The patient showed marked neurological improvement and was discharged on May 11. She was doing well at a routine hospital visit two years after the operation. Discussion True aneurysm of the posterior communicating artery itself is rare. Krayenbuhl reported 64 cases of so-called posterior communicating aneurysm, but only 7 of these were true PCoAAs (10.9%) (7). The 208 Fig. 2. Case 2. AP(A) and lateral (B) left carotid angiogram il- lustrates a small saccular aneurysm of the posterior communicating artery. ( C ) Postoperative angiogram. overall incidence of the aneurysm is only 2.8 % . Pia reported only two fusiform aneurysms among his 450 cases (0.4%) (8). Yasargil reported only 8 cases among a series of 173 carotid-posterior communicating aneurysms (4.6%) (12). As the posterior communicating artery gives rise to many important branches supplying the optic chiasm, oculomotor nerve, mammillary body, tuber cinereum, cerebral crura, ventral thalamus and the rostra1 portion of the caudate nucleus, preservation of these vessels is the key for successful treatment of the aneurysm (4, 5, 10). In addition, as the branch number is independent on the size of posterior communicating artery (9), preservation of the artery is important even if it is hypoplastic. In Case 2, the aneurysm was saccular and neck clipping was possible. But, in Case 1, True PCA aneurysm the aneurysm was not truly saccular but fusiform, and in consequence it was obliterated by trapping. The surgeon cannot ignore ischemic complications associated with impairment of the perforating arteries when trapping of aneurysms is performed. However, if trapping is the only method of obliteration in fusiform cases, and treatment of the aneurysm is something of a dilemma. If trapping is necessary, it should be performed as carefully as possible to preserve perforating arteries, especially the thalamoperforating arteries. As the oculomotor nerve runs near the posterior communicating artery, preservation of this nerve is another important surgical consideration. The operator should choose the best approach to the interpeduncular cistern. The route is decided by the relationship of the optic nerve, internal carotid artery, oculomotor nerve and tentorial edge (12). In addition, direction of the fundus, position of the neck of the aneurysm and perforators restrict the choice of the route. In both of our cases, the well developed posterior communicating arteries were recognized medial to the oculomotor nerve as described by other reports (9, 11). To reduce postoperative oculomotor disturbance, approach to the posterior communicating artery via opticocarotid route may be recommended (1 1). However, if the optic nerve and internal carotid artery are closely approximated, the approach must be lateral to the internal carotid artery (12). In addition, in the case of proximal PCoAA, the approach may also be lateral to the internal carotid artery as in the case of carotid-posterior communicating artery aneurysm. In Case 1, the approach was made via the opticocarotid route, but oculomotor nerve palsy was encountered. In Case 2, the aneurysm was attacked lateral to the internal carotid artery without postoperative oculomotor palsy. From our experience, preservation does not depend sorely on the route to the interpeduncular cistern. Both of the present cases were operated by the ordinary frontotemporal craniotomy. Although the Sylvian fissure was well dissected, moderate retraction of the temporal lobe was needed. If the surgeon hopes to reduce the degree of retraction, the more extensive exposures illustrated by Al-Mefty may be helpful (2). References 1. ABIKOS, ORITAT. A case of “true” posterior communicating aneurysm. Neurological Surgery (Tokyo) 1981: 9: 11811185. 2. AL-MEFTY0. Supraorbital-pterional approach to skull base lesions. Neurosurg 1987: 21: 474-477. 3. FOXJL. Intracranial aneurysms. New York: Springer-Verlag, 1983: 1: 138-139. 4. GIBOH, LENKEYC, RHOTONAL. Microsurgical anatomy of the supraclinoid portion of the internal carotid artery. J Neurosurg 1981: 55: 560-574. 5. HUBERP. Cerebral angiography. New York: Georg Thieme Verlag, 1982: 74-75. 6. KATAYAMA K, SAKURAI Y, SUZUKIJ. Case report: aneurysm of the posterior communicating artery itself - report of a successfully treated case. 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