40279676

PET/CT Findings of a Solid Pseudopapillary Tumor Mimicking Adrenocortical Carcinoma

Zhenpeng Jiang, MD, Huimin Shan, MD, Jingfa Li, MD, Yayi Xiao, MD, and Xusheng Zhu, MD

Abstract: Solid pseudopapillary tumor (SPT) is a rare low-grade malignant neoplasm originating predominantly in the pancreas. Extra-pancreatic SPTs are exceedingly rare clinical entities. The 18F-FDG PET/CT imaging features of extra-pancreatic SPTs remain poorly characterized in the current literature. We present a diagnostically challenging case of left adrenal SPT demonstrating MRI and 18F-FDG PET/CT features indistinguishable from adre- nocortical carcinoma, ultimately resulting in preoperative misdiagnosis.

Key Words: 18F-FDG, PET/CT, solid pseudopapillary tumor, extra-pancreatic, adrenal

(Clin Nucl Med 2025;50:748-750)

Received for publication March 17, 2025; accepted March 25, 2025.

From the Department of Nuclear Medicine, Guangzhou First People’s Hospital, School of Medicine, South China University of Techno- logy, Guangzhou, Guangdong, China.

Conflicts of interest and sources of funding: The authors declare that there are no conflicts of interest with respect to the research, authorship, and publication of this article.

Correspondence to: Xusheng Zhu, Department of Nuclear Medicine, Guangzhou First People’s Hospital, School of Medicine, South China University of Technology, Guangzhou, Guangdong 510180, China. E-mail: 13725152705@163.com.

Copyright @ 2025 The Author(s). Published by Wolters Kluwer Health, Inc. This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

DOI: 10.1097/RLU.0000000000005920

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FIGURE 1. A 41-year-old woman was referred for evaluation of a left adrenal mass found incidentally on a routine abdominal ultrasound. MRI revealed the absence of the normal left adrenal gland, replaced by a mass measuring ~8.3 x 7.1 x 11 cm. The lesion demonstrated slight hyperintensity on T1WI, heterogeneously elevated signal intensity on T2WI (A, white arrow), and preserved signal intensity on chemical shift out-of-phase sequences. Contrast-enhanced MRI (B, white arrow) revealed a heterogeneous progressive enhancement with nonenhancing foci. The lesion demonstrated restricted diffusion on DWI. The lesion was well-demarcated from the surrounding pancreas, spleen, and left kidney. Therefore, the lesion was initially considered suggestive of an adrenocortical carcinoma. Consequently, 18F-FDG PET/CT was performed for metabolic characterization and staging. MIP imaging (C) demonstrated a hypermetabolic mass in the left adrenal region, with no abnormal hypermetabolic areas elsewhere. Axial images (D, CT; E, PET; F, fusion) revealed the lesion (C, E, black arrows; D, F, white arrows) demonstrating significant FDG uptake with an SUVmax of 10.5. Punctate calcifications were observed within the lesion. Delayed imaging showed increased uptake (SUVmax 11.5). The 18F-FDG distribution pattern within the lesion was heterogeneous, with areas of no uptake. Based on these multimodal imaging features, the preoperative diagnosis was confirmed as adrenocortical carcinoma.

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FIGURE 2. The patient subsequently underwent curative resection. Gross appearance revealed an intact capsule surrounding the mass, with a multinodular cut surface. Microscopic images (A) showed that tumor cells exhibited a characteristic solid and pseudopapillary growth pattern. A small amount of adrenal cortical tissue was observed at the periphery of the tumor. Immunohistochemistry demonstrated diffuse vimentin positivity (B), transcription factor E3 (TFE3) reactivity (C), cytoplasmic ß-catenin retention (D), and focal inhibin-a expression. The histopathologic diagnosis confirmed an adrenal solid pseudopapillary tumor (SPT). SPT is a rare, low-grade malignant tumor, predominantly affecting young women.1,2 The majority of SPTs originate in the pancreas, with < 1% occurring outside the pancreas.3 Previous studies4-7 reported that extra-pancreatic SPTs predominantly occur in the ovaries, testes, the greater omentum, gastrointestinal tract, and retroperitoneum, while primary adrenal SPTs remain exceedingly rare. The 18F-FDG PET/CT findings in extra- pancreatic SPT have been poorly characterized. A study by Dong et al,8 which included 8 cases of SPTs, showed considerable FDG uptake variation (SUVmax range: 2.4-18.2). This variability may be related to the proportion of solid versus cystic components: SPTs with more solid components and fewer cystic elements typically demonstrating higher FDG uptake, while SPTs with more cystic components or hemorrhage tend to show lower uptake.8-10 However, 18F-FDG uptake alone cannot reliably distinguish benign from malignant SPTs, as both benign and malignant SPTs can demonstrate intense FDG uptake.2,11 Due to the extremely low incidence and atypical imaging features, the diagnosis of extra-pancreatic SPT is challenging.12 Although the PET/CT findings in this case were difficult to distinguish from those of adrenocortical carcinoma, the prognosis for the 2 conditions is markedly different.13 Our case suggests that when facing patients with similar imaging findings, even if adrenal SPTs are very rare, they should be considered in the differential diagnosis.

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