Objective: There is consensus that asymptomatic carriers of SDHB mutations should undergo periodic surveillance imaging. MRI has the advantage of avoiding radiation exposure but its sensitivity and specificity for detecting phaeochromocytoma and paraganglioma (PPGL) are dependent on sequences performed and expertise of reporting radiologists. We aim to highlight the additional value of diffusion-weighted imaging (DWI) for MR based surveillance, demonstrating DWI's ability to identify small PPGLs at all body sites. Design:We presented DWI sequences taken as part of SDHB surveillance to a radiologist, expert in reporting PPGL screening scans. Areas of high signal on DWI were interrogated using other standard MRI sequences. Patients:We reviewed the MRI scans for 18 SDHB mutation carriers with a total of 18 histologically proven SDHB-related tumours and 12 presumed PGLs/metastatic deposits. Results:The DWI sequences identified all 30 lesions. False-positive lesions were excluded by standard sequences. The tumours detected by DWI ranged in size from 5 to 52 mm. PPGLs were identified on DWI in the abdomen (n = 14), adrenal gland (n = 1), thorax (n = 3), neck (n = 2) and bladder (n = 2). Additionally, other SDHB-related tumours (GIST, RCC) were also highlighted by DWI, as were metastatic deposits in the liver and bone. Conclusions:These preliminary data suggest that DWI has high sensitivity and can identify even small SDHB-related tumours. If these findings are confirmed in larger series, for all SDH subunits, it will provide reassurance about identifying small SDHrelated tumours, without exposing patients to the consequences of radiation-based imaging and will secure the role of MRI for surveillance imaging. K E Y W O R D S DWI, imaging, MRI, paraganglioma, SDH, surveillance | 105 TUFTON eT al.

Objective Phaeochromocytomas and paragangliomas (PPGL) are rare, but strongly heritable tumours. Variants in succinate dehydrogenase (SDH) subunits are identified in approximately 25% of cases. However, clinical and genetic information of patients with SDHC variants are underreported. Design This retrospective case series collated data from 18 UK Genetics and Endocrinology departments. Patients Both asymptomatic and disease‐affected patients with confirmed SDHC germline variants are included. Measurements Clinical data including tumour type and location, surveillance outcomes and interventions, SDHC genetic variant assessment, interpretation, and tumour risk calculation. Results We report 91 SDHC cases, 46 probands and 45 non‐probands. Fifty‐one cases were disease‐affected. Median age at genetic diagnosis was 43 years (range: 11–79). Twenty‐four SDHC germline variants were identified including six novel variants. Head and neck paraganglioma (HNPGL, n = 30, 65.2%), extra‐adrenal paraganglioma (EAPGL, n = 13, 28.2%) and phaeochromocytomas (PCC) (n = 3, 6.5%) were present. One case had multiple PPGLs. Malignant disease was reported in 19.6% (9/46). Eight cases had non‐PPGL SDHC‐associated tumours, six gastrointestinal stromal tumours (GIST) and two renal cell cancers (RCC). Cumulative tumour risk (95% CI) at age 60 years was 0.94 (CI: 0.79–0.99) in probands, and 0.16 (CI: 0–0.31) in non‐probands, respectively. Conclusions This study describes the largest cohort of 91 SDHC patients worldwide. We confirm disease‐affected SDHC variant cases develop isolated HNPGL disease in nearly 2/3 of patients, EAPGL and PCC in 1/3, with an increased risk of GIST and RCC. One fifth developed malignant disease, requiring comprehensive lifelong tumour screening and surveillance.

Summary At least 40% of phaeochromocytomas and paraganglioma’s (PPGLs) are associated with an underlying genetic mutation. The understanding of the genetic landscape of these tumours has rapidly evolved, with 18 associated genes now identified. Among these, mutations in the subunits of succinate dehydrogenase complex (SDH) are the most common, causing around half of familial PPGL cases. Occurrence of PPGLs in carriers of SDHB, SDHC and SDHD subunit mutations has been long reported, but it is only recently that variants in the SDHA subunit have been linked to PPGL formation. Previously documented cases have, to our knowledge, only been found in isolated cases where pathogenic SDHA variants were identified retrospectively. We report the case of an asymptomatic suspected carotid body tumour found during surveillance screening in a 72-year-old female who is a known carrier of a germline SDHA pathogenic variant. To our knowledge, this is the first screen that detected PPGL found in a previously identified SDHA pathogenic variant carrier, during surveillance imaging. This finding supports the use of cascade genetic testing and surveillance screening in all carriers of a pathogenic SDHA variant. Learning points: SDH mutations are important causes of PPGL disease. SDHA is much rarer compared to SDHB and SDHD mutations. Pathogenicity and penetrance are yet to be fully determined in cases of SDHA-related PPGL. Surveillance screening should be used for SDHA PPGL cases to identify recurrence, metastasis or metachronous disease. Surveillance screening for SDH-related disease should be performed in identified carriers of a pathogenic SDHA variant.