CASE 1: A 50-year-old male was referred to the endocrine clinic with decreased libido and erectile dysfunction. Physical examination showed normal sense of smell, testicular size and secondary sexual characters. Investigations revealed low testosterone (10.6 mmol/l), SHBG 29.6 nmol/l, LH (6 IU/l) and FSH (7 IU/l) with high prolactin (4000 mU/l). The rest of the anterior pituitary hormones were normal. A MRI scan of the head showed a pituitary microadenoma with arachnoid cyst in the middle cranial fossa. Diagnosis of hypogonadotrophic hypogonadism secondary to microprolactinoma was made and he was subsequently treated with bromocriptine and testosterone. No intervention was needed for the arachnoid cyst
CASE 2: A 45-year-old male presented with decreased libido with unremarkable physical examination, including testicular size and secondary sexual characters. He was found to have isolated hypogonadotropic hypogonadism (FSH 5 IU/l, LH 6 IU/l, testosterone 8.4 nmol/l, SHBG 30 nmol/l) with the rest of the pituitary functions being normal. A MRI showed a normal pituitary and a large middle cranial fossa arachnoid cyst He was started on testosterone replacement which led to an improvement in his symptoms. Again, no intervention was necessary for the arachnoid cyst.
Discussion: Arachnoid cysts are commonly encountered fluid collections in the central nervous system. It has diverse presentation depending on its location. It represents 1% of intracranial mass. In a case series of 90 patients with hypopituitarism sellar arachnoid cysts was the cause for hypopituitarism due to pressure effects on the pituitary glands in two patients. Furthermore middle cranial fossa arachnoid cysts have been reported in patients with pituitary disease including prolactinomas and hypopituitarism. The association of pituitary disease and arachnoid cysts in the middle cranial fossa may represent correlation rather than co incidence and warrant further large scale study. In the meanwhile it may be reasonable to consider investigations for pituitary disease in these patients.