Penile Carcinoma Presented with Ilioinguinal Lymphadenopathy, Below-knee Skeletal Metastases, and Peritoneal Superscan on ¹⁸F FDG PET/CT

Introduction

Penile carcinoma is a rare malignancy predominantly affecting elderly men, with incidence rates ranging from 0.3 to 1 per 100,000, accounting for approximately 0.2% of all malignancies worldwide.[12] Among all cancer-related mortalities, penile carcinoma is responsible for <2% of deaths.[2] Histopathologically, penile squamous cell carcinoma (PSCC) represents the most common subtype, comprising over 95% of cases, whereas rarer histological variants, including sarcoma and melanoma, account for the remaining 5%.[3]

Metastatic dissemination of penile carcinoma typically occurs through lymphatic spread to regional nodes, particularly the superficial and deep inguinal lymph nodes, with subsequent involvement of the iliac nodes.[3] Hematogenous dissemination is less frequent and generally observed in advanced-stage disease.[4] Common sites of distant metastases include the liver, lungs, and bones, whereas involvement of the skin, peritoneum, and brain is exceedingly rare.[45] The presence of metastatic disease serves as a critical prognostic indicator and is associated with significantly reduced survival.[6] Consequently, the use of a reliable imaging modality is imperative for the accurate exclusion of distant metastases.

In the context of PSCC, ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) has demonstrated promising utility in lymph node staging and the detection of distant metastases due to the typically high metabolic activity of PSCC lesions.[7] A previous meta-analysis highlighted the diagnostic performance of ¹⁸F FDG PET/CT, reporting a pooled sensitivity of 81%, specificity of 92%, and overall accuracy of 90% for the identification of metastatic lymph nodes.[8] Accordingly, ¹⁸F FDG PET/CT serves as an essential imaging tool for the assessment of metastatic disease, offering critical prognostic and diagnostic insights that facilitate optimal clinical management.

Herein, we present an intriguing case of PSCC, in which ¹⁸F FDG PET/CT played a vital role in delineating rare and atypical metastatic involvement, thereby underscoring the aggressive nature of the primary malignancy.

Case Report

A previously healthy 46-year-old male presented with a 1-month history of progressive penile swelling, penile pain, and dysuria. Two weeks after his initial presentation, he developed severe bilateral leg pain, ultimately resulting in an inability to ambulate. Upon referral to our cancer center, physical examination revealed a large ulcerative penile lesion with an irregular and necrotic appearance. No palpable or tender inguinal lymphadenopathy was detected. The patient subsequently underwent a partial penectomy. Histopathological examination of the surgical specimen confirmed the diagnosis of invasive, moderately differentiated PSCC.

For oncologic staging and disease assessment, a ¹⁸F FDG PET/CT scan was performed. Maximum intensity projection images demonstrated extensive abdominopelvic hypermetabolism [Figure 1a, asterisk] alongside multiple hypermetabolic skeletal lesions [Figure 1a, arrows]. No focal hypermetabolic lesions were observed at the surgical site, apart from diffuse physiologic ¹⁸F FDG uptake at the distal urethra [Figure 1b, arrowhead]. In addition, multiple bilateral hypermetabolic ilioinguinal lymph nodes were identified [Figure 1c and d; curved arrows]. Notably, intense and diffuse ¹⁸F FDG uptake was observed throughout the greater omentum [Figure 1a and e-h; asterisks]. This pronounced peritoneal ¹⁸F FDG sequestration led to physiologic suppression of cerebral and hepatic uptake, a phenomenon indicative of a “peritoneal superscan.” Furthermore, multiple hypermetabolic skeletal lesions affecting both hemipelves, the right humeral head, and both tibial shafts were identified [Figure 1a and i-m; arrows].

Close

Figure 1 (a) Maximum intensity projection image from ¹⁸F Fluorodeoxyglucose (¹⁸F FDG) positron emission tomography/computed tomography scan demonstrates extensive abdominopelvic hypermetabolism (a, asterisk) and multiple hypermetabolic skeletal lesions (arrows). (b) No focal hypermetabolic lesions are noted at the site of partial penectomy, except for diffuse physiologic ¹⁸F-FDG uptake at the distal urethra (arrowhead). (c and d) Axial pelvic images depicted bilateral hypermetabolic ilioinguinal lymph nodes (curved arrows). (e-h) Axial and sagittal abdominopelvic views exposed an intense and diffuse ¹⁸F-FDG uptake observed throughout the greater omentum (asterisks), with concurrent cerebral and hepatic ¹⁸F-FDG suppression indicative of a “peritoneal superscan” phenomenon. (i-m) Axial and coronal views identified multiple hypermetabolic skeletal lesions involving both hemipelves, the right humeral head, and both tibial shafts (arrows)

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During a multidisciplinary tumor board meeting, a consensus was reached to initiate palliative chemotherapy with cisplatin and gemcitabine. However, the patient declined all therapeutic and palliative interventions. Tragically, he succumbed to his illness 45 days later at home.

Discussion

In this interesting case, ¹⁸F FDG PET/CT played a pivotal role in detecting clinically insignificant metastatic nodal dissemination. Despite the absence of palpable or tender inguinal lymph nodes, ¹⁸F FDG PET/CT identified bilateral hypermetabolic ilioinguinal lymphadenopathy. Notably, bilateral lymphatic involvement is frequently observed in advanced PSCC and is associated with significantly poorer prognosis, with 3-year survival rates decreasing from 54% in unilateral cases to 21% in bilateral cases.[9] Given that a prior meta-analysis has established a 90% accuracy rate for nodal disease detection, our findings reinforce the diagnostic utility of ¹⁸F FDG PET/CT, even in cases lacking overt clinical signs.[8] Another crucial observation obtained through molecular imaging was the presence of a peritoneal superscan, a phenomenon previously reported in fulminant peritoneal lymphoma, metastatic solid malignancies, and mesenteric tuberculosis.[10111213] Our review of the current literature revealed only a single prior case of peritoneal metastases in PSCC, manifesting as a solitary, painful, periumbilical nodule on CT imaging.[14] To the best of our knowledge, this represents the first documented instance of a peritoneal superscan attributable to fulminant peritoneal metastases in PSCC. In our case, ¹⁸F FDG PET/CT facilitated early-stage detection of peritoneal metastatic spread, even in the absence of any relevant clinical signs, peritoneal nodules, ascites, or abdominal lymphadenopathy.

Skeletal metastases represent another adverse prognostic factor in PSCC, predominantly affecting the axial and proximal appendicular skeleton.[15161718] However, our case was distinguished by an atypical metastatic pattern, with involvement extending below the knee. Appendicular skeletal metastases in PSCC contribute to significant morbidity, often resulting in loss of ambulation, as observed in our patient. A previously reported case described femoral metastases with unilateral lytic lesions and pathological fractures.[18] In contrast, our patient exhibited bilateral tibial shaft metastases with pathological fractures, evident as hypermetabolic foci on ¹⁸F FDG PET/CT, and presented with severe pain and an inability to ambulate. Generally, below-knee metastases are rare in solid malignancies due to the limited red marrow content and reduced vascular supply in distal extremities.[19] While lung metastases are often considered a prerequisite for distal skeletal dissemination, cases without pulmonary involvement suggest alternative skip metastasis pathways.[20]

Conclusion

This case highlights an aggressive and widespread metastatic pattern in PSCC, including peritoneal superscan, below-knee metastases, and bilateral inguinopelvic lymphadenopathy. These findings emphasize the critical role of ¹⁸F FDG PET/CT in staging and prognostication, advocating for broader application of molecular imaging in various clinical contexts to enhance early detection and therapeutic decision-making.