A 65-year-old man presented with a 6-month history of lower abdominal, pelvic, and perineal pain. His medical history was unremarkable. He had previously been evaluated for prostate disease by a urologist, but no abnormalities were found. At admission, his urinalysis yielded normal findings; however, ultrasonography revealed thickening of the bladder wall. Cystoscopy demonstrated edematous regions in the anterior wall of the bladder. Sagittal T2-weighted MRI showed a high-intensity, irregular-shaped mass with a maximum diameter of 5.4 cm that extended from the posterosuperior aspect of the pubic symphysis to the anteroinferior aspect of the bladder. T1-weighted imaging revealed a mass of similarly low intensity as the bladder wall. However, the central part of the mass exhibited decreased signal. On fat-suppressed T1-weighted imaging, gadolinium contrast material revealed enhancement in the majority of the mass. However, the central part of the mass showed decreased intensity on unenhanced T1-weighted imaging and lacked contrast enhancement, thereby suggesting a cystic component. CT showed degenerative changes accompanied by erosion of the pubic symphysis and pubic osteophytes. His serum tumor marker levels were normal; however, serum CRP was 4.25 mg/dL (normal range: 0.0–0.3) and ALP was 745 U/L (normal range: 120–340). After case review, the multidisciplinary team recommended drainage of the atypical cyst and pathological examination to rule out malignancy. The pelvic pain hindered the patient’s mobility; thus, prompt diagnosis and treatment were necessary. He therefore underwent exploratory laparotomy. We reached the pelvic cavity in laparoscopic procedure. No abscess was observed in the pelvic cavity; however, a cyst with inflammatory, hard fibrous tissue was observed around the pubic symphysis. We collected tissue specimens using forceps and placed a drainage tube over the cyst as laparoscopic fenestration. Only a small amount of serous drainage flowed out, and the drainage tube was removed after a few days. A biopsy sample of the lesion was obtained, and pathological findings revealed inflammatory fibrous tissue with lymphocytes but no malignancy. The culture of the biopsy also yields negative results. The comprehensive diagnosis was retropubic parasymphyseal cyst associated with inflammation. The patient was treated with cefazolin sodium 1 g IV q8h starting 1 day before surgery and continuing to postsurgical day 7. The patient’s symptoms rapidly improved, with serum CRP and ALP levels improving significantly. We continued antibiotic therapy minocycline 100 mg PO q12h for 1 month for optimal results. Over the next 2 months, the patient’s symptoms resolved, and serum CRP and ALP levels normalized.