Appendix mass: This is often the most common cause of a right iliac fossa lump, resulting from an appendiceal abscess or a phlegmon that forms as a complication of acute appendicitis. The body may wall off the inflamed appendix, creating a palpable mass.

Ileocecal tuberculosis: This condition can cause a mass in the right iliac fossa due to the formation of a cold abscess or due to the thickening of the ileocecal wall.
Carcinoid tumor: Although less common, carcinoid tumors can present as a lump in the right iliac fossa, especially if they originate from the appendix or the ileum.
Intussusception: This condition, where a part of the intestine telescopes into another, can cause a palpable mass, particularly in children but also in adults, often in the right lower quadrant.
Meckel's diverticulum: Complications of a Meckel's diverticulum, such as inflammation or obstruction, can lead to the formation of a mass in the right iliac fossa.

Intestinal lymphoma: Lymphomas can cause masses in the abdomen, including the right iliac fossa, and are critical to diagnose due to their potential for aggressive behavior and the need for specific treatment.
Perforated viscus: Although not typically presenting as a lump initially, a perforated viscus can lead to the formation of an abscess or mass in the right iliac fossa as the body tries to contain the infection.
Ovarian torsion or ovarian cyst: In females, these conditions can present with acute pain and a mass in the right iliac fossa, requiring urgent surgical intervention to preserve ovarian function.

Retroperitoneal sarcoma: These are rare tumors that can grow in the retroperitoneal space and occasionally present as a mass in the right iliac fossa.
Actinomycosis: A rare bacterial infection that can cause chronic inflammation and formation of a mass in the right iliac fossa.
Hydatid cyst: In endemic areas, hydatid cysts caused by Echinococcus granulosus can occasionally present as a lump in the right iliac fossa if they involve the intestines or adjacent structures.