What could be causing sudden lower right quadrant abdominal pain after flexion of the hip?

Sudden Lower Right Quadrant Abdominal Pain After Hip Flexion

Primary Diagnostic Consideration

Pain with hip flexion strongly suggests psoas muscle involvement, making psoas abscess or retroperitoneal pathology the leading diagnosis rather than typical intra-abdominal causes like appendicitis. 1

Clinical Significance of Hip Flexion Pain

• Hip flexion pain indicates iliopsoas muscle involvement, which causes hip flexion weakness and pain with hip extension—a critical distinguishing feature from typical appendicitis 1
• This presentation requires urgent evaluation for retroperitoneal pathology that can affect the lumbar plexus (L2-L4 nerve roots) or cause femoral neuropathy from compression or inflammation 1
• The combination of right lower quadrant pain with thigh weakness is a red flag for alternative pathology beyond standard intra-abdominal causes 1

Immediate Diagnostic Approach

Obtain contrast-enhanced CT of the abdomen and pelvis with IV contrast immediately, as this is the imaging modality of choice for this specific presentation. 1

• CT demonstrates 85.7-100% sensitivity and 94.8-100% specificity for acute abdominal pathology in right lower quadrant pain 2, 1
• CT can identify retroperitoneal collections, psoas abscesses, and alternative diagnoses beyond appendicitis 1
• Do not delay imaging beyond initial clinical assessment, as psoas abscesses can rapidly progress to sepsis and require prompt drainage 1

Differential Diagnosis to Evaluate

Primary Considerations (Given Hip Flexion Pain):

• Psoas abscess: Most likely given the specific hip flexion pain pattern 1
• Retroperitoneal pathology: Including hematoma, tumor, or inflammatory process affecting the iliopsoas muscle 1
• Femoral neuropathy: From compression or inflammation of the femoral nerve 1

Secondary Considerations:

• Appendicitis with retroperitoneal extension or perforation 3, 4
• Right colonic diverticulitis 3, 2
• Ureteral stone with referred pain 3
• Colitis or inflammatory bowel disease 3, 2

Management Algorithm Based on CT Findings

If Psoas or Retroperitoneal Abscess Identified:

• Initiate broad-spectrum antibiotics immediately 1
• Percutaneous catheter drainage (PCD) is usually appropriate for collections >3 cm 1
• Monitor for sepsis development and organ failure 2

If Appendicitis Confirmed:

• Proceed to appendectomy as standard treatment 1, 4
• For perforated appendicitis with abscess, PCD followed by delayed surgery or PCD only is usually appropriate 1
• Preoperative CT reduces negative appendectomy rates from 16.7% to 8.7% 2

If Alternative Diagnosis Found:

• Manage according to specific findings (diverticulitis, ileitis, colitis, bowel obstruction, ischemia, inflammatory bowel disease, or gynecologic pathology) 2, 5

Critical Pitfalls to Avoid

• Do not assume appendicitis based solely on right lower quadrant pain and fever—the hip flexion pain is a critical distinguishing feature that demands evaluation for psoas or retroperitoneal pathology 1
• Do not delay imaging in favor of prolonged clinical observation—psoas abscesses require prompt identification and drainage to prevent septic complications 1
• Do not rely on clinical examination alone—the negative appendectomy rate based on clinical determination without imaging is unacceptably high at 25% 3
• Do not order ultrasound as the initial study in adults—it has inadequate sensitivity for retroperitoneal pathology and will likely require follow-up CT 6

Additional Clinical Assessment Points

• Assess for fever and leukocytosis, which increase likelihood of infectious etiology 2, 1
• Examine for hip extension pain, which further supports psoas involvement 1
• Evaluate for thigh weakness, which suggests lumbar plexus or femoral nerve involvement 1