A Rare Case of Incidental Ectopic Posterior Pituitary in an Adult

Introduction : Ectopic posterior pituitary (EPP) is a rare anomaly that is usually diagnosed in childhood and typically associated with aberrant pituitary stalk development, anterior pituitary hypoplasia and functional deficits, and craniofacial abnormalities.  We present a case of incidental EPP diagnosed in an adult patient.

Case Description : A 57-year-old female underwent MRI for evaluation of headache and right ocular pain.  A normal-sized anterior pituitary was present in the sella turcica, but the pituitary stalk could not be visualized and T1 weighted high-signal corresponding to the neurohypophysis was ectopically adjacent to the superior margin of the anterior pituitary.  The patient reported an unremarkable gestation and birth, was of slightly below average stature for a woman in the United States (163 cm, 64 in), had two children and no problems with infertility, and denied polyuria and nocturia.  She reported an automobile accident with head trauma at age 20 years, though she was not informed of head imaging abnormalities.  Primary hypothyroidism was well compensated on supplemental thyroxine, and gonadotropins were appropriately elevated for postmenopausal status.  Measurements of IGF-1 and prolactin were within their respective laboratory reference ranges, but 8 AM cortisol (0.9 μg/dL, expected > 15) and ACTH level ( < 5 pg/mL, 10-65) indicated isolated secondary adrenal insufficiency (AI).  Diagnosis of AI was confirmed by a 250 μg Cosyntropin™ stimulation test (30 min stimulated cortisol 4.3 μg/dL, 60 min 6.1 μg/dL, expected > 18).  There was no history of recent or extended treatment with exogenous glucocorticoids.

Discussion : EPP may result from incomplete inferior extension of the diencephalon during embryologic development or occur after events such as pituitary surgery or severe head injury that result in transection of the pituitary stalk.  Mutations in multiple genes involved in neuronal migration and pituitary development, including HESX1, GLI2, and PROP1, have been identified in congenital cases of EPP.  Anterior pituitary deficits were identified in over 80% of patients in one pediatric series of EPP patients, with corticotroph axis deficiencies in approximately two-thirds of patients.  Diabetes insipidus is uncommon and occurs in fewer than 10% of EPP cases.  This patient’s case of EPP is highly unusual because it was diagnosed incidentally and well into adulthood.  Remote head trauma may have been the inciting event for EPP to occur, though this cannot be confirmed.  The diagnosis of isolated secondary adrenal insufficiency in this patient’s case illustrates the importance of screening anterior pituitary function in all patients with EPP.