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A right iliac fossa mass is any palpable or radiologically demonstrable abnormal lesion in the RIF region of the abdomen.

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The region extends from the right iliac crest superiorly, inguinal ligament inferiorly, midline medially, and anterior superior iliac spine (ASIS) laterally.
Contains: ileocecal junction, appendix, cecum, terminal ileum, ascending colon, right ovary and tube, iliac lymph nodes, retroperitoneal structures.

Classification

Etiological Classification

Origin	Conditions
Cecum / Appendix	• Appendicular mass (phlegmon, appendicular abscess).
• Carcinoma cecum.
• Cecal tuberculosis.
• Ameboma.
Ileum / Mesentery	• Crohn’s disease (ileocecal thickening, inflammatory mass).
• Ileal tuberculosis.
• Lymphoma of ileocecal region.
• Mesenteric cysts or tumors.
Gynecological (female)	• Ovarian cyst / neoplasm
• Tubo-ovarian mass (infective, abscess)
• Ectopic pregnancy (ruptured/organized)
Retroperitoneal / Others	Enlarged iliac lymph nodes (lymphoma, metastasis)
Psoas abscess
Retroperitoneal sarcomas

Clinical Features

Appendicular mass/abscess: h/o acute pain, fever, tender firm ill-defined mass.
Carcinoma cecum: elderly, anemia, weight loss, hard irregular non-tender mass.
Ileocecal TB: chronic illness, diarrhea, pulled-up cecum on imaging.
Ovarian mass: related to menstrual history, mobility transverse to axis.
Psoas abscess: psoas spasm, limb held flexed, pain on extension.

Radiology

Etiology	Clinical Clue	Imaging Clue
Appendicular mass / abscess	Acute appendicitis history	Ill-defined, inflammatory phlegmon, abscess with air-fluid level
Carcinoma cecum	Elderly, anemia, weight loss	Irregular cecal wall thickening, apple-core lesion
Ileocaecal TB	Young, chronic illness	Pulled-up contracted cecum, necrotic mesenteric nodes
Ameboma	Endemic areas, dysentery history	Eccentric cecal/colonic soft-tissue mass
Crohn’s disease	Relapsing abdominal pain, diarrhea	Segmental ileal thickening, comb sign, creeping fat
Lymphoma	B symptoms, systemic	Large homogeneous soft-tissue mass, less obstruction
Ovarian mass	Female, menstrual link	Complex adnexal cystic/solid mass
Psoas abscess	H/o TB/spine disease	Rim-enhancing collection in psoas muscle

Management

Appendicular mass: conservative (Ochsner–Sherren regimen), interval appendectomy.