Pelvic Mass After Prostatectomy

Abstract

A 66-year-old man was doing well 6 months after robotic radical prostatectomy for prostatic carcinoma and synchronous left radical nephrectomy for renal cell carcinoma. However, on surveillance computed tomography, he was noted to have a new pelvic mass that was concerning for a recurrent malignant neoplasm. He denied having pelvic pain, urinary symptoms, or bowel symptoms. His prostate-specific antigen level was undetectable. Subsequent magnetic resonance imaging revealed a heterogeneously enhancing mass within the prostatic bed, which had central necrosis ( Figure). The mass measured 4.8 × 5.5 × 5.0 cm and was contiguous with the right obturator internus. No appreciable lymphadenopathy was noted. Computed tomography-guided biopsy revealed spindle cells with a low mitotic index. Of note, the patient's son has a history of neurofibromatosis 1. The result of immunohistochemical staining was diffusely positive for desmin and smooth muscle actin, as well as focally positive for pan-keratin and S100. The staining result was negative for CD34 and CDK4. Fluorescence in situ hybridization failed to demonstrate MDM2 (OMIM 164785) gene amplification. Magnetic resonance imaging of the pelvis reveals a large heterogeneously enhancing mass within the prostatic bed. Axial (A and B) and sagittal (C and D) views reveal that the mass has T1 isointensity to hypointensity and T2 hyperintensity, suggesting internal areas of necrosis. A marked mass effect is seen on the anterior-inferior bladder, which displaces the bladder superiorly. The mass is contiguous with the right anterior aspect of the obturator internus and with the inner cortex of the midline superior pubic rami, which demonstrate erosion of the midline but no appreciable enhancing marrow signal.