Arachnoid cyst complicated with an inner aneurysm: case report

Abstract

The arachnoid cyst complicated with an inner aneurysm and intracystic hematoma is rarely encountered. In 2005, we treated such a patient by craniotomy through the left pterion approach. The possible causes of the intracystic hematoma and the reasons of the delay of the diagnosis are discussed. CASE REPORT A forty-year-old woman complaining of discontinuous muscular spasms accompanied by dizziness and vomiting for four months was admitted to our hospital on November 13, 2005. The patient showed sudden tic of the limbs, unconsciousness, foam spitting from her mouth, and reduplication of aconuresis-persevering within a few minutes. After the first attack, the patient was sent to a local hospital and underwent CT scan, which showed a low-density occupying mass at the temple on the left side without specific evidence of subarachnoid hemorrhage (Fig. 1). Because the similar attacks occurred frequently, she was referred to our hospital for an operation.Fig. 1.: Noncontrast CT showing a low-density mass at the temple on the left side.On admission, physical examination showed mind-body distinctness, normal cranial nerve functions, negative Kerning and Brudzinski signs, and no neck stiffness. MRI found a short T1 and long T2 signal at the suprasellar cistern and left temporal pole with distinct edge (Figs. 2 and 3). Abnormal blood vessel was not seen on magnetic resonance angiography (MRA), and no evidence of an aneurysm was found (Fig. 4). Thus, the patient was diagnosed as having occupying mass at the saddle area and left side temple and symptomatic epilepsy.Fig. 2.: MRI showing a short T1 signal at the suprasellar cistern and left temporal pole.Fig. 3.: MRI showing a long T2 signal at the suprasellar cistern and left temporal pole.Fig. 4.: Abnormal blood vessel was not detected by MRA.Four days after the admission, the patient received a craniotomy via the pterion approach. During the operation, an arachnoid cyst containing remote hemorrhage at the suprasellar cistern and left temporal pole was found. After opening the parietal wall of the arachnoid cyst and eliminating the remote hemorrhage, we detected a saccular aneurysm of the left posterior communicating artery, which directed outward. We carefully demeshed the neoplasm neck and clipped the aneurysm, and then excised the parietal wall of the arachnoid cyst. After opening the aneurysm cavity, we saw a lot of thrombus inside it. Postoperative pathological examination of the excised parietal wall confirmed that the mass was an arachnoid cyst. The patient's postoperative course was uneventful, and no vasospasm occurred. She was discharged two weeks later and recovered well without any neurological deficits or epilepsy. DISCUSSION The suprasellar cistern and temporal pole are the predilection site of arachnoid cyst, aneurysms usually locate in the internal carotid, anterior cerebral, and middle cerebral arteries. In 1995, Hirose and colleagues1 reported a saccular aneurysm at the bifurcation of the internal carotid artery, which ruptured into the arachnoid cyst at the middle fossa without causing a subarachnoid hemorrhage. Such a case has also been reported in 2000.2 Remote intracystic hemorrhage may be due to the aneurysm rupture, however, since the unsupported fragile blood vessels surrounding the arachnoid cyst may bleed spontaneously or after a relatively minor trauma,3 the cause of hemorrhage is often uncertain. Patients with intracranial arachnoid cysts may present with headache, seizures, and focal neurological signs; the arachnoid cyst may result in epilepsy if no high density was found on CT initially; and the aneurysm usually leads to subarachnoid hemorrhage because of its rupture. However, in our patient, because the hemorrhage is limited to the cystic cavity, subarachnoid hemorrhage and subdural hematoma was not detected by CT and MRI. Since the brain parenchyma was compressed but no hydroncus signs were found, we believed that the capsule wall was kept intact. The undetection of the aneurysm by MRA may be due to the intra-aneurysm thrombus and the relatively lower resolving power of MRA comparing with that of digital subtraction angiography (DSA). The delay of the diagnosis in this case is attributed to the absences of meningitic signs and evidences of subarachnoid hemorrhage on CT and MRI, and the normal intracranial vasculature shown by MRA. Therefore, we consider that DSA is more reliable than MRA for preoperative examination of aneurysms. If a patient had intracystic hemorrhage that is suspected as a aneurysm, DSA is recommended. For the arachnoid cyst complicated with inner aneurysm, aneurysm clipping should be performed firstly, followed by the ablation of the arachnoid cyst.