Appendicitis: This is often the first consideration for a lump or pain in the RLQ due to the appendix's typical location. The presence of a lump could indicate an appendicular mass, which forms as a result of the body's attempt to localize the infection.

Mesenteric Lymphadenitis: Inflammation of the lymph nodes in the mesentery can cause a palpable mass in the RLQ, often mimicking appendicitis.
Intestinal Obstruction: A lump could be a sign of an obstructed intestine, possibly due to adhesions, hernias, or tumors, which can cause significant abdominal pain and a palpable mass.
Ovarian Cyst or Torsion: In females, a lump in the RLQ could be related to ovarian pathology, such as a cyst or torsion, which requires urgent attention.
Diverticulitis: Although more common in the left lower quadrant, diverticulitis (inflammation of a diverticulum in the digestive tract) can occasionally present in the RLQ, especially if the sigmoid colon extends to this area.

Ectopic Pregnancy: A life-threatening condition that must be considered in females of childbearing age presenting with abdominal pain and a mass, even if the likelihood is low.
Ruptured Viseral Organ (e.g., Ruptured Appendix): Failure to diagnose a ruptured appendix or other visceral organ can lead to severe peritonitis and sepsis.
Malignancy (e.g., Lymphoma, Carcinoid Tumor): Although less common, malignancies can present as a lump in the RLQ and are critical not to miss due to their significant implications for treatment and prognosis.

Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause inflammation, obstruction, or bleeding, presenting as a lump in the RLQ.
Intussusception: A condition where a part of the intestine telescopes into another, which can cause a palpable mass and is more common in children but can occur in adults, often associated with a lead point such as a tumor.
Desmoid Tumor: A rare, benign tumor that can occur in the abdominal wall or within the abdomen and may present as a firm, palpable mass.