Introduction

   It is a tradition in medical terminology to nominate intracranial aneurysms according to the name of the arterial branch adjacent to the neck of the aneurysm. The posterior communicating artery (PCoA) aneurysms are actually internal carotid artery (ICA) aneurysms that develop at the junction of the ICA and the PCoA.
   The authors report a case with a 'true PCoA aneurysm', i. e. an aneurysm of PCoA itself, they had a chance to manage, review the medical literature, and discuss on the clinical implications of these aneurysms.

Case Report

   This 57-year old woman had chronic hypertension managed by oral medications. She suffered from headache 2 weeks prior to admission to our hospital. She had been admitted in a local hospital for a week, and discharged when her headache had relieved; the cause of her headache remained unknown.
   Sudden severe global headache recurred spontaneously on the day of admission, being accompanied by nausea and vomiting. On admission, her blood pressure was 200/110, and she was lethargic (GCS 14). Her brain computed tomography (CT) showed diffuse Fisher group III subarachnoid hemorrhage (SAH, Fig. 1). On hospital day (HD) 2, her follow-up brain CT revealed ventriculomegaly and scanty intraventricular hematoma (IVH). Transfemoral cerebral angiography (Fig. 2) revealed a superiorly directing 5 mm-sized saccular aneurysm attached at the proximal part of right PCoA just apart form the ICA trunk；the right posterior cerebral artery was fetal type.

1. Operation
   Usual right frontotemporoparietal craniotomy and pterional approach were performed on HD 2. Beginning from opening the carotid cistern, the neck of the aneurysm and adjacent normal anatomical structures were dissected and confirmed. The body of the aneurysmal sac was adhered to the third cranial nerve, which was carefully separated. A fenestration type Sugita's aneurysm clip with 7 mm-long straight blade was applied across the neck of the aneurysm parallel to the PCoA with cares not either to cause any parent arterial stenosis or to leave any residual neck unclipped；the ICA was encircled by the fenestration of the aneurysm clip with its external size well preserved. Intraoperatively, no PCoA perforators were definitely injured.

2. Post-operative Course
   On post-operative day (POD) 1, she was alert to drowsy；brain CT showed residual SAH, IVH in the posterior horns of lateral ventricles and a small low density at right anterior thalamus. On POD 3, lumbar drain was installed to drain CSF continuously.
   Her post-operative course was very much complicated thereafter. On POD 4, she became stuporous；brain CT showed IVH and a large right frontal intracerebral hematoma (ICH) with a remarkable mass effect. Emergency operation was performed for the removal of ICH, expansion duroplasty and decompression craniectomy；close observation on the previously clipped aneurysm revealed no problems. Immediate post-operative brain CT showed no residual ICH, small ventricles, residual SAH with IVH, and diffuse brain swelling. Sedation with intravenous anesthetics started and continued for the following 3 days. Thereafter she suffered from various complications, i.e. delayed epidural hematoma, infarcts at right frontal and occipital areas probably due to post-SAH vasospasm, hydrocephalus, pneumonia and sepsis, and pulmonary thromboembolism, which were managed intensively. Post-operative angiography on POD 101 showed a good obliteration of the aneurysm sac (Fig. 3). Around post-SAH day 127 when she was clinically stable, cranioplasty was performed with an autologous bone flap stored in the bone bank (-76℃ deep freezer). Finally she was discharged on HD 153 with such residual deficits as diplopia due to the medial gaze palsy of her left eye and left hemiparesis for out patient departmental (OPD) follow up.

Discussion

   Poppen firstly described 2 surgically proven cases of true PCoA aneurysm.⁷⁾ Yoshida is known to have firstly nominated a PCoA aneurysm 2-3 mm apart from ICA-PCoA junction as 'true' PCoA aneurysm in 1979.⁹⁾ The authors could find a domestic report of a similar case⁴⁾ as well as several international reports.^{1)2)3)5)6)8)9)} Its incidence is reported to be 0-3.3% of all intracranial aneurysms, and 4.6-11% of so-called PCoA aneurysms.⁴⁾
   True PCoA aneurysms have been reported to be located close to the ICA, at the middle part of PCoA, or close to the posterior cerebral artery,⁸⁾ in the order of decreasing frequency.
   These aneurysms were not always easily differentiated from ICA-PCoA aneurysm on pre-operative angiograms and occasionally identified only in surgical fields.
   Muneda et al analyzed 21 cases reported theretofore to find that true PCoA aneurysms are directed inferiorly, posteriorly, or laterally.⁶⁾ Other authors reported that the majority of true PCoA aneurysms are directed laterally and recommended to be very careful in surgical neck clipping of such laterally directed lesions to avoid intraoperative premature rupture of the aneurysm or the third nerve injury.⁴⁾ Kudo reported a case of true PCoA aneurysm with post-operative third nerve palsy.⁵⁾ In the majority, the aneurysm could be surgically secured successfully.^{1)2)3)4)6)8)9)}
   The authors agree with other previous authors' descriptions that every effort should be made in the surgical neck clipping to preserve all fine perforators branching off the PCoA in order to prevent the possible occurrence of post-operative small thalamic, hypothalamic, or basal ganglial infarcts. This important principle pertains to such cases with superiorly directed lesions as this patient.
   Kamiyama reported transient emotional disturbance,³⁾ and Abiko & Orita reported mental deterioration, contralateral hemiplegia, ipsilateral third nerve palsy, and ipsilateral basal ganglial hemorrhagic infarct after trapping of PCoA performed to treat a true PCoA fusiform aneurysm,¹⁾ respectively. Muneda et al wrote that it is difficult to predict the possibility of post-operative ischemic complications when the PCoA is trapped for the treatment of fusiform or wide-necked lesions.⁶⁾

Conclusion

   A rare case with a ruptured true PCoA aneurysm is reported. The majority of these aneurysms can be surgically secured with successful clinical results. Much cares should be taken in surgical neck clipping of these aneurysms to avoid any injury of PCoA perforators and the third cranial nerve.

REFERENCES

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2. Akimura T, Abiko S, Ito H. True posterior communicating artery aneurysm. Acta Neurol Scan 84:207-9, 1991

3. Kamiyama K, Sakurai Y, Suzurai J. Aneurysm of posterior communicating artery itself-report of a successfully treated case. Neurol Med Chir(Tokyo) 20:81-4, 1980

4. Kang SD. True posterior communicating artery aneurysm. J Korean Neurosurg Soc 26:1007-10, 1997

5. Kudo T. An operative complication in a patient with a true posterior communicating artery aneurysm: case report and review of the literature. Neurosurgery 27:650-3, 1990

6. Muneda K, Yoshizu H, Terada H. True posterior communicating artery aneurysm. No Shinkei Geka 29:163-8, 2001

7. Poppen JL. Specific treatment of intracranial aneurysms: Experiences with 143 surgically treated patients. J Neurosurg 8:75-102, 1951

8. Takeda N, Tamaki N, Asada M, Kurata H, Matsumoto S. 'True' posterior communicating artery aneurysm presenting the abducens nerve palsy. No Shinkei Geka 13. 1331-4, 1985

9. Yoshida M, Watanabe M, Kuramoto S. 'True' posterior communicating artery aneurysm. Surg Neurol 11:379-81, 1979