ODP351 Silent Corticotroph Adenomas – Characteristics and Comparisons to Other Non-functioning Pituitary Adenomas: A Case Series

INTRODUCTION: Silent corticotroph adenomas (SCA) are characterised by an absence of cortisol excess yet show positive immunostaining for T-Box transcription factor (TPIT) and frequently adrenocorticotropic hormone (ACTH). Patients with a SCA commonly present with symptoms of mass effect such as headache or visual compromise or are identified incidentally on imaging. SCAs are high risk according to the WHO 2017 classification scheme. AIM: To assess our cohort of SCAs for differences in demographics, presenting symptoms and imaging results compared to other non-functioning pituitary adenomas (NFPA). METHODS: Surgically treated patients with NFPAs seen by endocrinology at an Australian Tertiary Centre between the years 2011-2021 were included in the analysis. SCA was diagnosed based on the absence of clinical and biochemical features of cortisol excess in combination with immunohistochemical staining including positive staining for ACTH. Other NFPA subtypes were defined by immunohistochemical staining and the absence of hormone overproduction. We compared demographic information, symptoms at presentation and tumour size as assessed by magnetic resonance imaging (MRI) between the SCA and all other NFPA groups. Where available, pre- and postoperative ACTH and cortisol levels were compared in the SCA and non-SCA groups. RESULTS: 31 patients were identified, 5 with SCA and 26 with other NFPA, all were macroadenomas. All 5 cases of SCA showed ACTH positivity, 2 of 5 cases were stained for TPIT, both were positive. Mean age at surgery for the SCA group was 50.8±10.9 years. Mean non-SCA age was 54.3±15.4 years. 3 of the 5 patients with SCA were women. The most frequent symptoms at presentation were headache (SCA: 40%; non-SCA 36%) and visual disturbances (SCA: 60%; non-SCA 68%). The mean maximal tumour diameter in the SCA group was 31.36±13.61 mm versus 24.65±6.80 mm in the non-SCA group on MRI. Cavernous sinus invasion was present in 60% of the SCA and 38.5% of the non-SCA group. In the SCA group pre-operative ACTH levels were 5.1±2.6 pmol/L (normal <12.1 pmol/L) and dropped to 2.5±1.8 pmol/L postoperatively. Cortisol levels were 344±205 nmol/L (normal 138-650 nmol/L) and dropped to 269±228 nmol/L. In the non-SCA group ACTH levels were 4.5±2.3 pmol/L preoperatively and 4.6±3.8 pmol/L postoperatively. Cortisol levels were and 538±168 nmol/L preoperatively and 403±179 nmol/L postoperatively. CONCLUSION: In this retrospective comparison, compared to other NFPAs the SCA group showed younger age, more frequent headaches, less visual compromise, larger tumour size and increased cavernous sinus invasion. These findings are consistent with the known aggressiveness of SCAs. The reduction in ACTH levels postoperatively support the concept that SCAs produce inactive forms of ACTH. Although this is a small case series, there may be merit in monitoring for relative increases in ACTH levels in patients with a history of SCA. Presentation: No date and time listed