Differential Diagnosis for 63 y.o. Male with Lower Abdominal Pain

Single Most Likely Diagnosis

• Prostate Cancer with Local Spread and Secondary Infections: The CT abdomen findings of hanging masses adjacent to the prostate and in the left perineum, suspicious for malignancy, possibly prostate in origin, combined with the patient's age and symptoms, make this a highly likely diagnosis. The presence of cystitis and possible diverticulitis or proctitis (suggested by rectal wall thickening and stool in the rectosigmoid) could be secondary to the primary malignancy.

Other Likely Diagnoses

• Urinary Tract Infection (UTI) / Cystitis: The urinalysis showing WBCs, bacteria, and a positive nitrite test strongly suggests a UTI. The CT findings of marked bladder wall thickening with mucosal hyperenhancement further support cystitis.
• Diverticulitis: The CT findings of wall thickening of the rectum and mild adjacent edema/inflammation changes, along with a large amount of stool in the rectosigmoid, are consistent with diverticulitis.
• Prostatitis: Given the proximity of the suspected malignancy to the prostate and the presence of UTI/cystitis, prostatitis is a possible diagnosis, especially if the malignancy is of prostate origin.

Do Not Miss Diagnoses

• Septicemia: With a high WBC count (17.5) and evidence of infection (UTI/cystitis, possible diverticulitis), there is a risk of septicemia, which is life-threatening and requires immediate attention.
• Obstruction of the Urinary Tract: If the suspected prostate malignancy is causing obstruction, it could lead to severe consequences, including renal failure, and needs to be addressed promptly.
• Metastatic Disease: Given the suspicion of malignancy, the possibility of metastatic disease to other parts of the body (e.g., the small right pleural effusion could be indicative of metastasis) is a critical consideration for prognosis and treatment planning.

Rare Diagnoses

• Lymphoma: Although less likely, the presence of hanging masses and the patient's overall condition could, in rare cases, suggest lymphoma, particularly if the masses are found to be lymph nodes involved by lymphoma.
• Metastatic Disease from Other Primary Sites: While the prostate is a likely source of the primary malignancy, metastatic disease from other primary sites (e.g., colorectal cancer) could also present with similar findings, especially the rectal wall thickening and perineal masses.