Utility of ¹⁸F-FDG PET/CT in identifying penile squamous cell carcinoma metastatic lymph nodes

Due to the significant potential morbidity of inguinal and pelvic lymphadenectomy, the search for an imaging modality that can accurately identify penile squamous cell carcinoma (SCCA) lymphatic metastases continues. Initial (18)F-FDG PET/CT studies have reported 80% sensitivity and 100% specificity in the detection of inguinal and obturator lymph node metastasis. We review a single institutional experience of (18)F-FDG PET/CT imaging of SCCA of the penis to assess for accuracy and potential impact on clinical management.

Three patients diagnosed with penile SCCA at a single institution underwent staging (18)F-FDG PET/CT and went on to subsequent inguinal lymph node dissection. The (18)F-FDG PET machine was a Philips Gemini Time-of-Flight PET with LYSO crystals with 4.7 mm spatial resolution. The CT was a 16-slice helical CT with 5 mm slice widths. (18)F-FDG PET/CT findings were compared with the histologic findings of these procedures. Decision to proceed with lymphadenectomy was based on clinical judgment of a single urologist and all fused (18)F-FDG PET/CT imaging was assessed by a single experienced radiologist.

No patient received chemotherapy or radiation before the (18)F-FDG PET/CT or surgery. The first patient was obese (BMI > 30), clinically node negative, and the (18)F-FDG PET/CT showed inflammation. Histologic examination showed a positive 2 cm right inguinal metastatic node. The second patient's (18)F-FDG PET/CT showed a suspicious 1 cm left inguinal node. Histologically, the suspicious lymph node was positive for SCCA as was a second positive 2 cm lymph node not identified on preoperative (18)F-FDG PET/CT. Clinical exam of this patient was negative. The third patient was (18)F-FDG PET/CT and clinically negative but subsequently developed a palpable lymph node approximately 1 month later, which was suspicious on repeat (18)F-FDG PET/CT and positive for SCCA on histological examination.

(18)F-FDG PET/CT has shown initial promise in the staging of penile SCCA. However, our review shows that false negative studies occur at alarmingly high rates, and (18)F-FDG PET/CT is poor in detection of micro-metastasis. Thus, close follow-up in these patients is imperative.