Comparison of 68Ga-DOTANOC PET/CT and contrast-enhanced CT in localisation of tumours in ectopic ACTH syndrome

Abstract

BackgroundLocalising ectopic adrenocorticotrophic hormone (ACTH) syndrome (EAS) tumour source is challenging. Somatostatin receptor-based PET imaging has shown promising results, but the data is limited to case reports and small case series. We reviewed here the performance of 68Ga-DOTANOC positron emission tomography (PET)/computed tomography (CT) and contrast-enhanced CT (CECT) in our cohort of 12 consecutive EAS patients.Materials and methodsRetrospective data analysis of 12 consecutive patients of EAS presenting to a single tertiary care centre in a period between January 2013 and December 2014 was done. CECT and 68Ga-DOTANOC PET/CT were reported (blinded) by an experienced radiologist and a nuclear medicine physician, respectively. The performance of CECT and 68Ga-DOTANOC PET/CT was compared.ResultsTumours could be localised in 11 out of 12 patients at initial presentation (overt cases), whereas in one patient, tumour remained occult. Thirteen lesions were identified in 11 patients as EAS source (true positives). CECT localised 12 out of these 13 lesions (sensitivity 92.3%) and identified five false-positive lesions (positive predictive value (PPV) 70.5%). Compared with false-positive lesions, true-positive lesions had greater mean contrast enhancement at 60s (33.2 vs 5.6 Hounsfield units (HU)). 68Ga-DOTANOC PET/CT was able to identify 9 out of 13 lesions (sensitivity 69.2%) and reported no false-positive lesions (PPV 100%).ConclusionCECT remains the first-line investigation in localisation of EAS. The contrast enhancement pattern on CECT can further aid in characterisation of the lesions. 68Ga-DOTANOC PET/CT can be added to CECT, to enhance positive prediction of the suggestive lesions.

The role of 68Ga-DOTA derivatives PET-CT in patients with ectopic ACTH syndrome

“…series (4,7,13,14,23). In our study, a quarter of patients with EAS remained occult at the last available follow-up, as recently reported in a series with similar diagnostic approach (14).…”

“…CT detected 90% of NETs in overt EAS, whereas 68 Ga-SSTR-PET/CT identified 70% of cases, without reporting false-positive imaging, resulting useful to increase the specificity of the suggestive CT-positive lesions. In this series, the only EAS not detected with conventional imaging remained occult also after the 68 Ga-SSTR-PET/CT (13). In a recent multicenter study, Wannachalee et al reported in 28 patients that 68 Ga-SSTR-PET/CT is sensitive to detect primary and metastatic neoplasms in EAS and to identify occult tumours after other type of imaging (in 65% of cases), achieving a significant clinical impact in the diagnostic-therapeutic management in the majority of patients (14).…”

“…We reported 14 patients with overt and covert EAS: 11 patients with bronchial carcinoids (9 new cases and 2 recurrences), 2 SCLCs and 1 case of pancreatic NET. A systematic review of EAS in 2015 found a lower sensitivity of CT than 68 Ga-SSTR-PET/CT (10), but other studies presented discordant results (13). The more common use of CT in EAS may be explained by the prevalent distribution of neoplasms in the thorax, where MR is problematic because of its less resolution in the lung parenchyma, due to respiratory and cardiac artefacts (7).…”

“…ACTH-secreting neoplasms present several receptors, especially SSTRs, the target of theranostic somatostatinbased diagnosis (with octreoscan 68 Ga-SSTR-PET/CT (10,13,14)) or treatment (with somatostatin analogs (15,16)). In EAS, excessive glucocorticoid levels can directly down-regulate SSTR expression, especially type 2, thus resulting in a possible false-negative 68 Ga-SSTR-PET/CT in EAS patients with active hypercortisolism that could revert after normalization of cortisol levels achieved with steroidogenesis inhibitors (17).…”

MANAGEMENT OF ENDOCRINE DISEASE: Cushing’s syndrome due to ectopic ACTH secretion: an expert operational opinion

“…Before prescribing additional imaging procedures, we strongly suggest a second careful examination of the thoracic CT-scan, which is the main source of occult EATs, ideally by several radiologists, to limit the risk of false negatives. Elsewhere, false positives on CT have been described in 3.6% of cases (149,155), a finding that emphasizes the importance of using an appropriate CT protocol and the experience of the radiologist to limit the frequency of thoracic lures. Additionally, it should be emphasized that imaging of the thorax in the search for an EAT may be particularly complex in patients with a pulmonary embolism or infection (see previous section).…”