INTRASELLAR ARACHNOID CYST - A CASE-REPORT

Neurological examination revealed bilateral decreased visual acuity and visual field defect. Endocrinological examination showed panhypopituitarism. Other neurological findings were normal. X-ray film of the skull showed a ballooning dilation of the sella turcica with thinning of the sellar floor. CT scan showed a cystic lesion with CSF-density occupied the sella. After intravenous administration of contrast medium, the cyst showed no enhancement. MRI showed the intrasellar mass had the same characteristics as the surrounding subarachnoid space. Bilateral carotid angiographies demonstrated that the carotid siphons were stretched and displaced laterally, and the A1 portions of the anterior cerebral arteries were raised. We made a diagnosis of intrasellar cystic lesion. On August 18, the sella turcica was opened via the transsphenoidal rhinoseptal approach. The cyst contained CSF-like fluid, and a part of the cyst wall was resected. The cavity was filled with Gelfoam and the sellar floor was repaired with bone flap. Postoperarively, the patient's visual disturbance improved, but diabetis insipidus appeared and required hormonal replacement. The patient was discharged on September 27 with improvement of visual acuity and visual field. Histological examination demonstrated that the cyst wall consisted of thick arachnoidal cells with fibrous connective tissue. The arachnoidal cells with oval nuclei was stained with epithelial membrane antigen. Symptoms, signs and radiological findings of intrasellar arachnoid cyst are similar to those of various sellar lesions including pituitary adenoma, craniopharyngioma, empty sella, Rathke's cleft cyst, epidermoid et al. Intrasellar arachnoid cyst can be suitably treated by a transsphenoidal approach. The indications for transsphenoidal exploration include the following: to relieve the compression to the optic chiasm, the pituitary stalk or gland, and to exclude the possibility of other sellar neoplasms. Clear differentiation between a true intrasellar arachnoid cyst and arachnoid diverticulum is difficult without complete histological examination of the cyst. In this case we presumed that the cyst was arachnoid diverticulum originated from empty sella because of the radiological appearance and surgical findings. This is the first case to demonstrate with MRI the natural course of the intrasellar arachnoid cyst.