Clinically Functioning FSH-Secreting Pituitary Adenoma

Background: Gonadotroph adenomas are the most common type of non-functioning pituitary adenomas. However functioning gonadotroph adenomas are rare with only a few cases reported in literature. Clinical Case: A 42-year old man was admitted as a case of COVID-19 when an incidental finding of a pituitary gland mass was detected. Upon evaluation, the patient was found to have blurred vision and dizziness since few years, however no history of headache, seizures, visual field deficit were reported, nor clear symptoms related to anterior pituitary hypo- or hyperfunction. Pituitary MRI revealed a pituitary gland mass measuring 30x23x22 mm expanding the pituitary fossa and extending to suprasellar cistern. Initial laboratory investigations revealed low free T3 (1.8 pmol/L, normal: 3.1-6.8 pmol/L) and low free T4 (6.6 pmol/L, normal: 12-22 pmol/L) with normal TSH (3.54 mIU/L, normal: 0.27-4.2 mIU/L), high FSH (31.4 IU/L, normal: 1-18 IU/L), and high total testosterone (50.31 nmol/L, normal 8.3-32.9 nmol/L). Testicular ultrasound showed bilateral enlarged testicles (right testis 38.14 cm(3) and left testis 33.38 cm(3)). Visual Field testing revealed monocular superior temporal defect affecting only the left eye. Patient was treated medically with levothyroxine and hydrocortisone and surgically by minimally invasive transsphenoidal resection of pituitary adenoma. Histopathology assessment confirmed the diagnosis of gonadotroph secreting adenoma, with positive immunostain for FSH. At 6 weeks postoperatively, insulin tolerance test was performed after which hydrocortisone was only prescribed during periods of stress. Anterior pituitary profile was repeated which revealed normalization of free T4 (14.3 pmol/L) and FSH (1.2 IU/L) and decrease in testosterone (0.66 nmol/L). Assessment of visual field revealed marked improvement of previous findings. Pituitary MRI was also repeated with findings of enhancing soft tissue remnants. At 12 weeks postoperatively, anterior pituitary profile revealed normalization of testosterone (11.3 nmol/L). Testicular ultrasound was repeated and showed a marked decrease in testicular volume (right testis 17.93 cm(3) and left testis 21.13 cm(3)). Conclusion: Functional gonadotroph adenomas are a rare subtype of pituitary adenomas which pose a diagnostic challenge and require meticulous clinical evaluation and multidisciplinary therapeutic approach.