What is the differential diagnosis of a wandering (mobile) palpable mass in the right iliac fossa?

Differential Diagnosis of a Wandering (Mobile) Mass in the Right Iliac Fossa

A mobile mass in the right iliac fossa most commonly represents an appendicular mass or abscess, but critical alternative diagnoses including cecal malignancy, ovarian pathology, and ileocecal tuberculosis must be systematically excluded through contrast-enhanced CT imaging. 1, 2

Most Common Etiologies by Frequency

Appendicular pathology accounts for approximately 63% of right iliac fossa masses, with appendicular masses representing 45.3% and appendicular abscesses 17.5% of cases. 2 The mobility characteristic suggests either:

• Appendicular mass/abscess - develops after acute appendicitis with periappendiceal inflammation 2
• Ileocecal tuberculosis - accounts for 12.9% of cases and presents as a mobile inflammatory mass 2
• Cecal carcinoma - represents 7.4% of cases, often with extraluminal extension mimicking inflammatory disease 3, 2

Critical Malignant Diagnoses That Cannot Be Missed

In 3 of 7 patients presenting with apparent inflammatory masses of the right iliac fossa, malignant lesions were discovered - small intraluminal tumors with wide extension beyond the cecal wall that mimicked benign inflammatory processes. 3 This 43% malignancy rate in one series underscores the danger of assuming inflammatory etiology without definitive imaging.

Appendiceal mucocele (0.2-0.3% of appendectomies) presents as a palpable right iliac fossa mass and is difficult to differentiate from malignant or benign adnexal masses clinically. 4 Rupture can cause pseudomyxoma peritonei, making accurate preoperative diagnosis essential.

Gender-Specific Considerations

In women of reproductive age, ovarian pathology accounts for 6.4% of right iliac fossa masses. 2 The differential must include:

• Ovarian cysts (complicated with rupture or hemorrhage) 1
• Adnexal torsion - requires urgent surgical intervention 1
• Tubo-ovarian abscess - appears as a mass with variable echogenicity, debris, and irregular margins 1

Less Common but Important Diagnoses

• Cecal diverticulitis with severe peridiverticulitis - can present identically to appendicular pathology 3
• Appendicular hydatid cyst - can mimic appendiceal mucocele, complicated ovarian cyst, or abscess 5
• Isolated Crohn's disease of the appendix - presents with inflammatory mass 6
• Parietal lipoma (4.6%), retroperitoneal tumors (1.8%), and ileocecal lymphadenopathy (1.8%) 2

Mandatory Diagnostic Approach

CT abdomen and pelvis with intravenous contrast is the definitive diagnostic modality with sensitivity 85.7-100% and specificity 94.8-100%. 7, 1, 8 This imaging must be performed in all cases before assuming inflammatory etiology. 3

Specific Imaging Findings to Identify:

On ultrasound, appendicular abscess manifests as:

• Cystic mass, mixed solid-cystic mass, or hypoechoic solid mass 6
• Appendiceal calculus appears as hyperechoic structure with acoustic shadowing 6
• Critical limitation: Acute appendicitis in females may mimic tubo-ovarian disease on ultrasound 6

On CT, look for:

• Multilocular cystic masses suggesting mucocele or hydatid cyst 5
• Extraluminal extension beyond cecal wall suggesting malignancy 3
• Cecal wall thickening with inflammatory changes 3

Essential Laboratory Workup

• Complete blood count - leukocytosis suggests infectious/inflammatory process 7, 1
• C-reactive protein - higher sensitivity and specificity than WBC for surgical pathology 1
• Pregnancy test (β-hCG) - mandatory in all reproductive-aged women before CT 1, 8
• Urinalysis - exclude urinary tract pathology 1

Clinical Red Flags Requiring Urgent Surgical Evaluation

• Signs of peritonitis (rigidity, rebound tenderness, guarding) 1
• Fever - suggests appendicitis, abscess, or pelvic inflammatory disease 7, 1
• Hemodynamic instability 1

Critical Pitfalls to Avoid

Never assume inflammatory etiology without contrast-enhanced CT - up to 43% may harbor occult malignancy. 3

Do not delay imaging for oral contrast administration - IV contrast alone provides equivalent diagnostic accuracy without treatment delay. 1, 8

Do not rely on ultrasound alone in adults - while useful for initial assessment, negative ultrasound does not exclude significant pathology. 1

In women, always obtain transvaginal ultrasound if gynecological pathology suspected before proceeding to CT. 1

Recommended Diagnostic Algorithm

1. Obtain detailed history: Duration of symptoms >1 day, fever >38°C, and prior episodes suggest appendicular pathology 7
2. Physical examination: Document exact location, mobility, size, tenderness, and peritoneal signs 1
3. Laboratory tests: CBC, CRP, β-hCG (women), urinalysis 1, 8
4. Imaging sequence:
   • Women of reproductive age with suspected gynecological pathology: Transvaginal ultrasound first 1
   • All other patients: CT abdomen/pelvis with IV contrast as primary modality 7, 1, 8
5. Surgical consultation: Immediate if peritonitis, delayed for tissue diagnosis if mass characteristics suggest malignancy 1, 3