Summary: Cushing's disease is a rare disorder characterised by excessive cortisol production as a consequence of a corticotroph pituitary tumour. While the primary treatment is surgical resection, post-operative radiation therapy may be used in cases of ongoing inadequate hormonal control or residual or progressive structural disease. Despite improved outcomes, radiotherapy for pituitary tumours is associated with hypopituitarism, visual deficits and, rarely, secondary malignancies. We describe an unusual case of a 67-year-old female with presumed Cushing's disease diagnosed at the age of 37, treated with transsphenoidal resection of a pituitary tumour with post-operative external beam radiotherapy (EBRT), ketoconazole for steroidogenesis inhibition, and finally bilateral adrenalectomy for refractory disease. She presented 30 years after her treatment with a witnessed generalised tonic-clonic seizure. Radiological investigations confirmed an extracranial mass infiltrating through the temporal bone and into brain parenchyma. Due to recurrent generalised seizures, the patient was intubated and commenced on dexamethasone and anti-epileptic therapy. Resection of the tumour revealed a high-grade osteoblastic osteosarcoma. Unfortunately, the patient deteriorated in intensive care and suffered a fatal cardiac arrest following a likely aspiration event. We describe the risk factors, prevalence and treatment of radiation-induced osteosarcoma, an exceedingly rare and late complication of pituitary irradiation. To our knowledge, this is the longest reported latency period between pituitary irradiation and the development of an osteosarcoma of the skull.

Learning points: Cushing's disease is treated with transsphenoidal resection as first-line therapy, with radiotherapy used in cases of incomplete resection, disease recurrence or persistent hypercortisolism. The most common long-term adverse outcome of pituitary tumour irradiation is hypopituitarism occurring in 30-60% of patients at 10 years, and less commonly, vision loss and oculomotor nerve palsies, radiation-induced brain tumours and sarcomas. Currently proposed characteristics of radiation-induced osteosarcomas include: the finding of a different histological type to the primary tumour, has developed within or adjacent to the path of the radiation beam, and a latency period of at least 3 years. Treatment of osteosarcoma of the skull include complete surgical excision, followed by systemic chemotherapy and/or radiotherapy. Overall prognosis in radiation-induced sarcoma of bone is poor. Newer techniques such as stereotactic radiosurgery may reduce the incidence of radiation-induced malignancies.

Keywords: 2020; ACTH; Adrenalectomy; Adult; Australia; Bicarbonate; Bone; CT scan; Cortisol; Cortisol (serum); Creatinine; Cushing's disease; Delirium; Dexamethasone; Estimated glomerular filtration rate; FSH; Female; Fludrocortisone; Glucocorticoids; Glucose; Histopathology; Hypercortisolaemia; Hypokalaemia; Hyponatraemia; Hypopituitarism; Hypothyroidism; Iatrogenic disorder; Immunohistochemistry; July; Ketoconazole; LH; Levitiracetam*; MRI; Metabolic alkalosis; Midazolam*; Mineralocorticoids; Noradrenaline*; Oedema; Oncology; Osteosarcoma*; Phenytoin*; Pituitary; Pituitary tumour (malignant); Potassium; Prednisolone; Radiology/Rheumatology; Radiotherapy; Renal insufficiency; Resection of tumour; Seizures; Sodium; TRH; TRH*; Thiamine*; Thyroxine (T4); Transsphenoidal surgery; Unique/unexpected symptoms or presentations of a disease; White.