A Case Report of a Solitary Pelvic Mass Proven to Be a Lymph Nodal Metastasis from Anal Cancer

A solitary pelvic-wall lymph nodal metastasis can be mistaken as a primary malignancy when a primary tumor has not been diagnosed. We report the case of a 72-year-old woman with a solitary left pelvic-wall mass that was finally proven to be a left internal iliac lymph nodal metastasis from anal cancer. No signs of the primary tumor had been initially found by general screening using computed tomography, colonoscopy, pelvic magnetic resonance imaging, and gynecological/urological examination; however, squamous cell carcinoma was detected by surgical biopsy of the left pelvic-wall mass. Additional ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG-PET) showed focal accumulations in the left pelvic mass and the anal canal. A biopsy of the induration in the anal canal led to the diagnosis of anal cancer, clinical T2N2M0, and stage IIIB (UICC-TNM 7th ed.), which was indicated for definitive chemoradiotherapy. Two months after completing a definitive chemoradiotherapy for anal cancer, a fixed induration developed under the surgical wound along with the surgical tract of the biopsy site. Physical examination and ¹⁸F-FDG-PET/computed tomography led to the clinical diagnosis of unresectable surgical tract recurrence of anal cancer. The patient underwent palliative treatment and died 14 months after the diagnosis of the surgical tract recurrence. In conclusion, anal cancer may present as a solitary pelvic mass without any anal symptoms. To evaluate the solitary pelvic mass, ¹⁸F-FDG-PET/computed tomography, along with digital examination, will probably help in establishing an accurate diagnosis. Anal cancer must be considered during the differential diagnosis of a solitary pelvic-wall mass for a correct diagnosis and to avoid unnecessary procedures.