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

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
The combination of right lower quadrant pain with thigh weakness is a red flag for alternative pathology beyond standard intra-abdominal causes 1

The American College of Radiology recommends obtaining 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

Psoas abscess is the most likely diagnosis given the specific hip flexion pain pattern 1
Retroperitoneal pathology, including hematoma, tumor, or inflammatory process affecting the iliopsoas muscle, should be considered 1
Femoral neuropathy from compression or inflammation of the femoral nerve is a possible diagnosis 1
Right colonic diverticulitis is a secondary consideration 3, 2

If psoas or retroperitoneal abscess is identified, initiate broad-spectrum antibiotics immediately and consider percutaneous catheter drainage (PCD) for collections >3 cm 1
If appendicitis is confirmed, proceed to appendectomy as standard treatment, and consider PCD followed by delayed surgery or PCD only for perforated appendicitis with abscess 1

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

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