What is the differential diagnosis for a young female presenting with sudden epigastric pain radiating to the back, nausea, vomiting, a palpable firm non-mobile mass in the right lower quadrant, and bloody mucoid stool?

Differential Diagnosis for Young Female with Sudden Epigastric Pain Radiating to Back, Nausea, Vomiting, RLQ Mass, and Bloody Mucoid Stool

This clinical presentation most urgently suggests intussusception as the primary diagnosis, given the classic tetrad of intense abdominal pain, vomiting, bloody mucoid stool, and palpable abdominal mass, though acute pancreatitis with a concurrent RLQ process must be immediately excluded. 1

Life-Threatening Diagnoses Requiring Immediate Exclusion

Intussusception (Most Likely Primary Diagnosis)

• Intussusception classically presents with intense intermittent abdominal pain, vomiting, bloody mucoid diarrhea, and a palpable abdominal mass—all four cardinal findings are present in this patient. 1
• The firm, non-mobile mass in the RLQ is characteristic of the intussuscepted bowel segment, which can be palpated in the right lower quadrant or right upper quadrant depending on the location. 1
• Bloody mucoid stool ("currant jelly stool") indicates mucosal ischemia and is a late finding that demands urgent intervention to prevent bowel necrosis. 1
• While most common in children under 5 years, intussusception occurs in young adults and is frequently missed when cardinal findings are attributed to other diagnoses. 1
• Obtain CT abdomen and pelvis with IV contrast immediately, which will show the pathognomonic "target sign" or "sausage-shaped" mass. 2

Acute Pancreatitis

• Epigastric pain radiating to the back is the hallmark presentation of acute pancreatitis and must be ruled out immediately with serum lipase ≥2x normal or amylase ≥4x normal. 3, 4
• Nausea and vomiting are present in the majority of pancreatitis cases. 3
• Mortality is <10% overall but reaches 30-40% in necrotizing pancreatitis, making early diagnosis critical. 4
• The RLQ mass and bloody stool are NOT explained by pancreatitis alone, suggesting a concurrent or alternative diagnosis. 3

Perforated Peptic Ulcer

• Presents with sudden, severe epigastric pain that becomes generalized, with mortality reaching 30% if treatment is delayed. 3, 4
• Physical exam should reveal abdominal rigidity and absent bowel sounds—if these are present, this diagnosis moves higher. 3
• CT with IV contrast shows extraluminal gas in 97% of cases, fluid or fat stranding in 89%, and focal wall defect in 84%. 3, 4
• Bloody mucoid stool is NOT typical of perforation unless there is concurrent bleeding ulcer. 4

Myocardial Infarction

• Never dismiss cardiac causes in young females with epigastric pain—MI can present atypically with epigastric pain as the primary manifestation, especially in women, with 10-20% mortality if missed. 3, 4, 5
• Obtain ECG within 10 minutes of presentation and serial cardiac troponins at 0 and 6 hours. 3, 4, 5
• The presence of GI symptoms (bloody stool, palpable mass) makes MI less likely but does not exclude it. 4

Other Critical Diagnoses to Consider

Appendiceal Mucocele

• Presents as pain and palpable mass in the right iliac fossa, occurring in 0.2-0.3% of all appendectomies. 6
• Difficult to differentiate from malignant or benign adnexal masses clinically. 6
• Can rupture causing pseudomyxoma peritonei, a surgical emergency. 6
• Does NOT typically cause bloody mucoid stool, making this diagnosis less likely. 6

Solid Pseudopapillary Pancreatic Tumor

• Rare pancreatic cystic neoplasm that typically presents in young females in their 20-30s. 7
• When symptomatic, presents with abdominal pain, palpable abdominal mass, nausea and vomiting. 7
• The epigastric location of pain and presence of nausea/vomiting fit, but bloody mucoid stool is NOT a feature. 7
• Complete surgical resection is curative with excellent long-term survival. 7

Small Bowel Obstruction with Ischemia

• Adhesions cause 55-75% of small bowel obstructions, hernias and tumors account for most others. 2
• Presents with intermittent abdominal pain, vomiting, and inability to pass gas or stool. 2
• Bloody mucoid stool suggests bowel ischemia, which is a surgical emergency. 2
• A palpable mass could represent distended bowel loops or an obstructing lesion. 2

Complicated Jejunal Diverticulitis

• Can present with severe epigastric pain, nausea, and projectile vomiting. 8
• Physical exam may reveal abdominal distension and bilateral upper quadrant tenderness. 8
• CT demonstrates mechanical small bowel obstruction. 8
• This is a poorly understood entity with non-specific presentation. 8

Immediate Diagnostic Algorithm

Step 1: Stabilize and Obtain Vital Signs

• Check for hypotension, tachycardia ≥110 bpm, or fever ≥38°C, which predict perforation or sepsis. 4
• Establish IV access and begin fluid resuscitation if hemodynamically unstable. 4
• Maintain NPO status until surgical emergency is excluded. 4

Step 2: Immediate Laboratory Testing

• Serum lipase and amylase to rule out pancreatitis (lipase ≥2x normal or amylase ≥4x normal). 3, 4
• Complete blood count (assess for leukocytosis suggesting infection/ischemia). 4
• Cardiac troponins at time 0 and repeat at 6 hours (do not rely on single measurement). 4, 5
• Serum lactate (elevated in bowel ischemia). 4
• ECG within 10 minutes of presentation. 3, 4, 5

Step 3: Immediate Imaging

• CT abdomen and pelvis with IV contrast is the gold standard when diagnosis is unclear, identifying intussusception, pancreatitis, perforation, and vascular emergencies. 2, 3, 4
• CT has 95% sensitivity and 94% specificity for appendicitis and other acute abdominal pathology. 2
• Look specifically for: target sign (intussusception), extraluminal gas (perforation), pancreatic inflammation, bowel wall thickening with pneumatosis (ischemia). 2, 3

Step 4: Surgical Consultation

• Immediate surgical consultation is mandatory given the combination of bloody mucoid stool (suggesting ischemia) and palpable mass (suggesting mechanical obstruction or intussusception). 1
• Intussusception with bloody stool indicates mucosal ischemia and requires urgent reduction (hydrostatic or surgical). 1
• Any evidence of perforation, bowel ischemia, or complete obstruction requires emergent surgical intervention. 2, 3

Critical Pitfalls to Avoid

• Do not attribute all symptoms to a single diagnosis—this patient may have concurrent pancreatitis AND intussusception, or pancreatitis causing a lead point for intussusception. 2, 1
• Never dismiss intussusception in young adults because it is "rare"—the cardinal findings are frequently not all present, particularly outside the usual pediatric age range, leading to missed diagnoses and ischemic complications. 1
• Do not delay imaging to pursue endoscopy—bloody mucoid stool with a palpable mass suggests bowel ischemia requiring immediate CT and surgical evaluation. 3, 1
• Do not assume the RLQ mass is gynecologic without imaging—appendiceal mucocele, intussusception, and bowel obstruction can all present with RLQ masses in young females. 6
• Never exclude cardiac causes based on age or presence of GI symptoms—obtain ECG and serial troponins in all patients with epigastric pain. 3, 4, 5