Background Postoperative spindle cell nodules (PSCNs) are benign proliferative lesions of the submucosal stroma that classically form within 1 to 3 months after a surgical procedure.1 PSCNs have been described in the literature at numerous sites; however, the bladder was the first and remains the most common site of origin in the existing literature. This unusual pseudosarcomatous lesion of the bladder was first described by Roth in 1980,2 and in 1984 Proppe et al3 coined the term PSCN in their description of 8 similar cases. While PSCNs can be safely observed, they are difficult to distinguish from malignant conditions.4 Such mimicry has resulted in massive interventions with irreversible impacts on patient quality of life5 and there exist fewer than 10 reports on the subject.5-12 Case A woman in her 30's with medical history notable for neurofibromatosis type 1 and a partially duplicated left-side collecting system was diagnosed with left-side ureteral obstruction on workup for acute kidney injury after cesarean section. The left ureteral orifice appeared inflamed on cystoscopic examination, and an abrupt distal ureteral occlusion was noted on retrograde pyelography. A nephrostomy tube was placed with plans for delayed repair. The patient underwent operative repair 3 months later through an open lower midline incision. Hydroureter was seen to the level of common iliac vessels several centimeters distal to bifurcation of the common ureteral channel. The bladder was densely adherent to the peritoneum and pubic bone, but once dissected free appeared unremarkable in size and mobility. A flexible ureteroscope was placed through the cystotomy for inspection of the right ureter and through the ureterotomy for inspection of the left ureteral common channel and both left upper tract ureters. Diagnostic ureteroscopy was unremarkable. Bladder elongation and psoas hitch was performed for a tension-free ureteroneocystostomy. This was protected with a flap of peritoneum and fibrin sealant. Her stent was removed after 6 weeks keeping the nephrostomy tube in place as is our standard practice. After failing a clamp trial, antegrade and retrograde studies were performed revealing a one-way valve at the ureterovesical anastomosis, allowing retrograde-only passage of contrast. She underwent revision ureteroneocystostomy, at which time a papillary lesion overlying an abnormal bulge of tissue was noted at the anastomosis (Figure 1). Several biopsies were obtained, and the anastomotic site was excised with a 2-cm circumferential margin. Antegrade nephrostogram after stent removal confirmed patency of the revision 8 weeks postoperatively. Pathologic examination of the lesion returned fibromyxoid and spindle cell proliferation (Figure 2). This was supported by smooth muscle actin, panCK, and CD10 positivity (Table 1). Owing to morphologic similarities with various types of sarcomas, the biopsy results were sent for review at a Genitourinary Pathology Consensus Conference which determined that this was consistent with PSCN. A plan for periodic surveillance cystoscopy was put in place because of the rarity of her biopsy results and the uncertain natural history of PSCN. She was doing well 9 months postoperatively with no suspicious lesions identified on surveillance cystoscopy and no evidence of hydronephrosis on surveillance renal US.Figure 1.: Cystoscopic view during investigation of the left ureterovesical anastomosis. A nodule of papillary-appearing mucosa is seen protruding from the right, occluding the ureteroneocystostomy.Figure 2.: Representative hematoxylin and eosin (H&E) demonstrating bland spindle cell (arrows) proliferation in a loose, edematous stroma. Pleomorphism, necrosis, and atypical mitotic figures are absent (20×). Table 1. - Immunohistochemistry Report S-100 Negative CD10 Positive P16 Positive B CAT Negative nuclear KI-67 Up to 10/hpf WT-1 Negative SM actin Positive PanCK Positive Discussion The differential diagnosis for a papillary bladder lesion encompasses many benign and malignant etiologies, including inflammatory pseudotumor, PSCN, myxoid leiomyoma, leiomyosarcoma, sarcomatoid carcinoma, fibrous histiocytoma, or rhabdomyosarcoma.1,4,13,14 PSCNs classically follow a benign course4 but can mimic aggressive malignancies both on cystoscopic appearance and microscopic inspection. PSCNs are believed to form by a reactive process secondary to recent surgical intervention.1,14 Nearly identical histology can be seen in lesions deemed inflammatory pseudotumors, where a reactive process takes place in the absence of known surgical intervention. Those with underlying genetic abnormalities, such as neurofibromatosis, may carry a higher risk of PSCN formation. Neurofibromatosis (von Recklinghausen disease) is an autosomal dominant disorder, which originates in neural crest cells and manifests with mesenchymal growths largely localized to the skin, eyes, and nervous system. Neurofibromas of the genitourinary tract are rare, but the bladder is most commonly involved.15-18 It is speculated that surgical intervention activates a neoplastic process in these patients because of alterations in the NF-1 gene with downstream effects on several growth factors; however, the molecular pathway for this has not been described.19 Of the few cases of bladder neurofibromas described in the literature, a benign course is detailed after diagnosis, suggesting conservative treatment with regular follow-up.13 On gross inspection, PSCNs may appear as polypoid or submucosal nodules with or without surface ulceration. Current immunohistochemical techniques are not sufficiently specific for PSCN but may provide some clues toward the diagnosis. Smooth muscle actin, for example, is a detector of smooth muscle neoplasms and myofibroblastic lesions and is commonly positive in lesions with a spindle cell morphology,20 as seen in the present case. This stains positive in 63% of inflammatory myofibroblastic tumors, 43% of sarcomas, and a variable number of PSCNs.21 PSCN and inflammatory pseudotumor often demonstrate positive reactivity for vimentin and cytokeratins AE1/AE3/Cam 5.2.4 Other contemporary reports suggest a role for anaplastic lymphoma kinase, which stains positive in most inflammatory tumor cases, or p53, which is less reactive in benign lesions.13 Instead, the diagnostic importance of H&E is paramount. PSCNs are characterized by diffuse spindle cell proliferation and elongated eosinophilic cytoplasmic elements with a vascular stroma, often in the setting of chronic inflammation.10 PSCNs have minimal cytologic atypia, atypical mitoses, tumor necrosis, or muscular invasion.21,22 While both PSCN and inflammatory pseudotumor are benign growths, their histologic patterns (hyperplastic urothelial changes and polypoid cystitis) can mimic malignancies such as leiomyosarcoma, sarcomatoid carcinoma, and rhabdomyosarcoma.13 Malignancies are suspected when focal or diffuse patterns of epithelial differentiation are present. Because there exists such a massive divergence in therapies between PSCN and the malignant conditions it mimics, much of the diagnostic scrutiny in this case relied on expert assessment of H&E stains, namely ruling out pleomorphism, atypical mitotic figures, and necrosis.