ACTH Producing Pituitary Adenoma Found After Transsphenoidal Resection of Meningioma

Introduction:
ACTH-dependent Cushing's disease (CD) is a condition characterized by pituitary hypersecretion of ACTH, leading to adrenal cortisol upregulation. Hypercortisolism has long-term complications, notably metabolic syndrome, cardiovascular disease, and osteoporosis, to name a few. The incidence of CD is approximately 1-2 cases per million. ACTH can be secreted by pituitary macroadenomas and microadenomas, and in some cases, ectopic sources.  This case report describes a case of ACTH-dependent CD caused by a pituitary microadenoma with a history of planum sphenoidal meningioma.

Case Description:
48-year-old female with a past medical history of planum sphenoidal meningioma s/p transsphenoidal partial resection, central hypothyroidism on levothyroxine, and hypogonadotropic hypogonadism presented with worsening truncal obesity and prediabetes. The physical exam was remarkable for obesity and hyperpigmentation of knuckles. Labs were significant for elevated AM cortisol at 27. 2 mcg/dL with a significantly elevated ACTH level of 81.8 pg/L. Saliva cortisol at 11pm was also mildly elevated at 0.154 ug/dL. The cortisol level was not suppressed with the low-dose dexamethasone suppression test at 8.5 mcg/dL, while High-dose dexamethasone suppressed cortisol to 2.0 mcg/dL, indicating a possible pituitary source. Other biochemical tests such as Prolactin, TSH, and HGH levels were normal. MRI of the pituitary was performed to locate the potential source and was significant for hypo-enhancing lesions suspicious for bilateral synchronous pituitary microadenomas (9x5 mm right and 4x4 mm left). To confirm that there are no ectopic sources for the ACTH, a PET Dotatate scan was done and showed hypermetabolic meningioma corresponding to the findings of the pituitary MRI and confirmed no other abnormal focal radiotracer uptake. Non-functioning pituitary tumors are common, hence, to confirm the pituitary source of ACTH prior to surgery, she underwent inferior petrosal sinus sampling (IPSS). This revealed a significantly elevated ACTH secretion from the right microadenoma. Transsphenoidal resection of the pituitary tumor was performed. Post-procedure, AM cortisol levels were undetectable and ACTH level was low at 5.8 pg/mL. She was then started on hydrocortisone for presumed adrenal insufficiency post pituitary lesion resection. No signs of diabetes insipidus were shown after surgery—the patient will follow up with endocrinology for eventual weaning off hydrocortisone. 

Discussion:
Simultaneous occurrence of pituitary adenoma and meningioma without a history of radiotherapy is extremely rare, with only 49 cases described before 2019. Even more rare, is an ACTH secreting pituitary adenoma coexisting with a meningioma. IPSS procedure was performed after MRI in this case to get even more accurate localization of the source before surgical excision, as it is the best test to differentiate pituitary from ectopic ACTH-dependent Cushing’s. In approximately 1 out of 3 patients, remission is not achieved with surgical excision alone. For this reason, patients need post-operative monitoring and secondary medications to control their symptoms.