Appendicitis: This is the most common cause of right iliac fossa pain and swelling, especially if the appendix is located in a retrocecal position. The inflammation of the appendix can lead to swelling and tenderness in the right iliac fossa.

Mesenteric Lymphadenitis: Inflammation of the lymph nodes in the mesentery can cause right iliac fossa swelling and pain, often mimicking appendicitis. It's commonly seen in children and young adults.
Right Ovarian Cyst or Torsion: In females, a cyst or torsion of the right ovary can present with swelling and pain in the right iliac fossa.
Intussusception: Although more common in children, intussusception (the telescoping of one portion of the intestine into another) can cause abdominal pain and swelling, potentially localized to the right iliac fossa if the intussusception occurs in the ileum.
Inflammatory Bowel Disease (Crohn's Disease or Ulcerative Colitis): These conditions can cause chronic inflammation and swelling in the abdomen, including the right iliac fossa, especially if the disease affects the terminal ileum or cecum.

Ectopic Pregnancy: Although less common, an ectopic pregnancy can present with abdominal pain and swelling, including in the right iliac fossa, and is a medical emergency.
Ruptured Ovarian Cyst: A ruptured ovarian cyst can cause severe pain and potentially life-threatening bleeding, making it a critical diagnosis not to miss.
Diverticulitis: Inflammation of a diverticulum in the sigmoid colon can sometimes present with pain and swelling that might be referred to the right iliac fossa, though it's more commonly associated with the left lower quadrant.
Intestinal Obstruction: Obstruction of the intestine can cause severe abdominal pain, vomiting, and potentially swelling, depending on the location and cause of the obstruction.

Right Iliac Fossa Hernia: A hernia occurring through a weakness in the abdominal wall in the right iliac fossa can cause a swelling in this area.
Lymphoma: Abdominal lymphoma can cause lymph node swelling, potentially leading to a palpable mass in the right iliac fossa.
Tuberculous Abdomen: Abdominal tuberculosis can cause chronic inflammation and swelling in the abdomen, including the right iliac fossa, though it's relatively rare in many parts of the world.
Actinomycosis: A rare bacterial infection that can cause chronic abdominal pain, swelling, and formation of sinus tracts, potentially involving the right iliac fossa.