Bladder Leiomyoma: A Rare Differential and a Potential Pitfall in the Evaluation for a Bladder Mass in ¹⁸F-Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography

A 65-year-old man presented with lower urinary tract symptoms. Ultrasonography showed the presence of 3.5 cm × 2.3 cm lobulated, hypoechoic lesion in the posterolateral wall of urinary bladder with Grade II prostatomegaly. Contrast-enhanced computed tomography (CT) abdomen revealed a polypoidal soft-tissue thickening (~3.8 cm × 3.3 cm × 2.4 cm) without any calcification involving the left posterolateral wall and the left vesico-ureteral junction. His serum prostate-specific antigen was 3.33 (normal range: 0.2–4.0 ng/ml). Subsequently, the patient underwent ¹⁸F-flurodeoxyglucose-positron emission tomography/CT (FDG PET/CT) for lesion characterization and staging. FDG PET/CT revealed mildly tracer-avid soft-tissue growth in the urinary bladder suspicious of a low-grade neoplasm [Figure 1]. The patient underwent transurethral resection of bladder tumor and the histopathology revealed features of urinary bladder leiomyoma [Figure 2].

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Figure 1 Fluorodeoxyglucose-positron emission tomography/computed tomography showing mildly tracer-avid (SUV_max 2.9) soft-tissue growth in the left posterolateral wall of the urinary bladder (shown with arrow) without any definite evidence of abnormal tracer uptake elsewhere in the corresponding axial positron emission tomography (a), axial fused positron emission tomography/computed tomography (b), contrast-enhanced axial computed tomography (c), the corresponding coronal fused positron emission tomography/computed tomography (d), and computed tomography (e)

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Figure 2 Histopathology of the lesion showing characteristic intersecting fascicular arrangement of spindle-shaped cells (H and E, ×40: a). On further magnification, elongated nuclei having fine delicate chromatin with blunted ends and significant collagenization are present (H and E, ×200: b). No nuclear atypia, mitosis, or necrosis was noted and a diagnosis of leiomyoma was made

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FDG PET/CT is an important investigation in the characterization and evaluation of various malignant conditions and its role in the evaluation of the urological malignancies has recently evolved.[1] However, the role of FDG-PET/CT in the benign pathologies of urinary bladder is hardly studied. Leiomyomas are rare benign mesenchymal neoplasms of urinary bladder comprising <0.5% of all bladder tumors,[2] with only approximately 250 being reported in the literature. In the index study, low-grade tracer-avid urinary bladder mass in FDG PET/CT and initial radiological investigations suggestive of malignant mass turned out to be urinary bladder leiomyoma in histopathology. With ever-increasing utility of PET/CT in oncology, it becomes equally important to have knowledge about different pathological disorders that may be seen in FDG studies. Along with the reported differential diagnosis of a bladder mass, adenocarcinoma of the bladder,[3] transitional cell/urothelial cancer,[4] leiomyosarcoma,[5] high-grade lymphoma,[6] etc., show high-grade FDG uptake. Among the differentials of a variably FDG-avid bladder mass, such as mucinous adenocarcinoma of bladder,[7] low-grade paraganglioma,[8] and low-grade preinvasive transitional cancer,[9] leiomyoma of the urinary bladder can also mimic as bladder cancer as seen in the index case. Thus, FDG uptake in a bladder tumor may not differentiate leiomyoma from urinary bladder malignancy.