What is the diagnosis for an 82-year-old male with a 5-day history of constipation (difficulty of defecation), passing flatus, weight loss, decreased appetite, and a fixed, non-movable, 2-inch mass on the left femoral area, with tenderness over the right and left lower quadrant areas?

Differential Diagnosis for 82-Year-Old Male with Difficulty of Defecation and Other Symptoms

Single Most Likely Diagnosis

• Colorectal Cancer: Given the patient's age, difficulty in defecation, passage of flatus, weight loss, decreased appetite, and a mass in the left femoral area which could be a metastasis, colorectal cancer is a strong consideration. The symptoms of bowel obstruction and the presence of a possible metastatic mass point towards an advanced stage of cancer.

Other Likely Diagnoses

• Diverticulitis: The patient's symptoms of difficulty in defecation, passage of flatus, weight loss, and tenderness over the lower quadrant areas could also suggest diverticulitis, especially if there's an involvement of the sigmoid colon.
• Bowel Obstruction: The difficulty in defecation and passage of flatus could indicate a bowel obstruction, which might be due to various causes including adhesions, hernias, or tumors.
• Metastatic Cancer: The presence of a mass in the left femoral area could indicate metastasis from a primary cancer site, which could be colorectal, given the other symptoms, but also could be from other primary sites.

Do Not Miss Diagnoses

• Appendicitis: Although less common in the elderly, appendicitis can present atypically and should not be missed due to its potential for severe complications if not treated promptly.
• Intestinal Ischemia: This condition can present with abdominal pain and changes in bowel habits, and given the patient's age, it's a critical diagnosis not to miss due to its high mortality rate.
• Intra-Abdominal Infection or Abscess: The patient's symptoms of tenderness and possible bowel obstruction could also indicate an intra-abdominal infection or abscess, which requires prompt diagnosis and treatment.

Rare Diagnoses

• Lymphoma: Although less likely, lymphoma could present with a mass, bowel obstruction symptoms, and systemic symptoms like weight loss and decreased appetite.
• Gastrointestinal Stromal Tumor (GIST): A rare tumor of the GI tract that could cause bowel obstruction and metastasis, presenting with similar symptoms.
• Carcinoid Syndrome: A rare condition caused by a neuroendocrine tumor that could lead to bowel obstruction, weight loss, and other systemic symptoms, though typically it would also include flushing and diarrhea.