Accessory spleen, [68Ga]-DOTATOC PET/CT and 99mTc-labelled Sn-colloid SPECT/CT

Abstract

Splenic nodules are defined as a benign and rare dissemination of splenic tissue, usually occurring after splenectomy or injury. These nodules can be distributed throughout the entire peritoneal cavity. Marked colloid scintigraphy with ^99mTc pertechnetate is a highly sensitive method for exploring the reticuloendothelial system and identifying splenic nodules. We report the case of a 64-year old man who underwent surgery in 2020 for a well-differentiated neuroendocrine tumor (Ki67 < 3%) of the pancreatic head. The surgery involved a left splenopancreatectomy. During MRI surveillance in 2021, a vascularized lesion measuring 19-mm was discovered near the surgical site, raising suspicion of neoplastic recurrence. Figure 1: A [⁶⁸Ga]-DOTATOC PET/CT is performed to characterize this suspicious lesion. In fact, in the case of a suspicious lesion in a patient with a history of neuroendocrine tumor, recurrence must be considered. [⁶⁸Ga]-DOTATOC PET/CT is widely used as a functional imaging in the detection and characterization of neuroendocrine tumors. It appears hypermetabolic as an oval-shaped nodule measuring 21 mm in the major axis, located in the left hypochondrium. A challenge in [⁶⁸Ga]-DOTATO PET/CT imaging is the expression of somatostatin receptors in cells unrelated to neuroendocrine tumors, such as in normal splenic tissue. This poses a diagnostic problem, especially when ectopic splenic tissue is present (in cases of accessory spleens or splenosis), as it can mimic neuroendocrine tumors or metastases. On MRI, splenic parenchyma is hypointense on T1- and hyperintense on T2-weighted images, this makes it difficult to distinguish between a splenosis nodule and a tumor recurrence. In these difficult cases, splenic scintigraphy plays an important role in the final diagnosis in a noninvasive way. Figure 2: Technetium-99m (Tc-99m) sulfur colloid is the most used radiopharmaceutical for imaging of the spleen. Following intravenous administration, the radiotracer is rapidly removed from the blood by the reticuloendo the system of the spleen, liver, and bone marrow. To explore the nature of the evolving nodule, so as not to miss a splenosis nodule or accessory spleen, a SPECT/CT with Tc-99m sulfur colloid is realized. The nodule appears intensely hyperxifant suggesting a splenic tissue origin. In fact, persistence of splenic tissue after splenectomy occurs in 5–20% of patients. Splenosis is defined as an auto-implantation of functional splenic tissue after.