MON-LB58 The Use of 11C Methionine PET CT In Localization of ACTH Dependent Cushing’s Disease

Background and objective: Hypercortisolism is the hall mark of ACTH Cushing’s syndrome, which is a benign ACTH secreting tumor resulting in high morbidity and mortality. The diagnosis is based on an elevated serum ACTH, elevated 24h urinary cortisol or a non-suppressible ACTH after dexamethasone suppression test. Confirmation of ACTH hypersecretion is followed by localization of the adenoma which can be pituitary in origin or peripheral. Dynamic MRI of the pituitary gland is the gold standard for diagnosis of pituitary tumors, and contrast enhanced CT scan is the gold standard for ectopic lesions which are usually lung tumors. The localization of the lesion is often a challenge because conventional MRI fail to show pituitary lesions and sometimes requiring inferior petrosal sinus sampling to confirm pituitary origin. Transsphenoidal surgery is the treatment of choice for Cushing’s disease, even without MRI evidence of pituitary tumors, if pituitary origin is confirmed by inferior petrosal sinus sampling. This causes increase in the incidence of treatment failure and complications. Thus, the diagnosis of Cushing’s disease urges exploring new diagnostic modalities. In our study we test the sensitivity of 11C methionine PET CT together with dynamic pituitary MRI in localization of ACTH dependent Cushing’s disease. Materials and methods This is an interventional, prospective study, forty-one subjects: newly diagnosed ACTH dependent Cushing’s Syndrome (n=29). (indicated by non-suppressible ACTH on dexamethasone suppression test) or persistent hypercortisolism following transsphenoidal surgery (n=12). 11C methionine PET CT was done in all cases in addition to dynamic pituitary MRI. All patients underwent 11 C-methionine PET-CT in addition to dynamic pituitary MRI This allowed us to determine whether suspected adenomas seen on structural imaging exhibited focal tracer uptake on functional imaging.Inclusion Criteria:• Aged 18 years old or over• Patient with a diagnosed Cushing’s disease confirmed by non-suppressible ACTH on dexamethasone suppression test.• Patient with persistent ACTH dependent Cushing’s disease following transsphenoidal surgery.• Patient not enrolled in other interventional studies.Exclusion Criteria:• Contraindication to MRI• Pregnant woman, breastfeeding RESULTS: Patients with newly diagnosed ACTH dependent Cushing: 24 out of 29 of the cases showed adenoma on dynamic MRI of the pituitary; 5 out of 29 cases failed to showed any lesions on dynamic MRI of the pituitary; Inferior petrosal sampling was done and confirmed pituitary origin in 4 out of 5 and 1 out of 5 was found to have ectopic ACTH secretion. In patients with persistent hypercortisolism following transsphenoidal surgery; 3 out of 12 of the cases showed adenoma on dynamic MRI of the pituitary and 7 out of 12 cases failed to showed any lesions on dynamic MRI of the pituitary and inferior petrosal sampling was done and confirmed pituitary origin in all 12 cases. All 41 cases underwent 11C methionine PET CT scan; 39 patients showed tracer uptake on 11c methionine PET CT scan in the pituitary area, 36 of which had unilateral asymmetrical tracer uptake. All 40 subjects with suspected pituitary lesions were confirmed to be of pituitary origin by histopathological examination of biopsies taken intraoperatively. CONCLUSIONS 11C methionine PET CT has proven to be of very high sensitivity in detecting ACTH secreting adenomas, further studies should be done on a larger scale as this modality can address the pitfalls in localization of ACTH secreting lesions.