What conditions can appendicitis mimic in a young adult or adolescent presenting with abdominal pain?

Conditions That Mimic Appendicitis in Young Adults and Adolescents

In young adults and adolescents presenting with right lower quadrant pain, you must systematically consider gastrointestinal, gynecological, urological, and musculoskeletal causes, as imaging studies reveal alternative diagnoses in a substantial proportion of cases initially suspected to be appendicitis.

Gastrointestinal Mimics

Common Inflammatory Conditions

• Mesenteric adenitis/gastroenteritis is one of the most frequent mimics in adolescents, presenting with right lower quadrant pain, fever, and leukocytosis similar to appendicitis 1
• Epiploic appendagitis causes acute focal abdominal pain that can mimic appendicitis or cholecystitis, but is self-limiting and requires only conservative management with analgesia 2
• Meckel diverticulum can present with right lower quadrant pain indistinguishable from appendicitis on clinical examination alone 1

Bowel-Related Pathology

• Inflammatory bowel disease (Crohn's disease) commonly affects the terminal ileum and can present identically to acute appendicitis with right lower quadrant pain and inflammatory markers 3
• Intussusception, while more common in younger children, can occur in adolescents and presents with colicky abdominal pain 1
• Cecal diverticulitis presents with right lower quadrant pain and is increasingly recognized in younger patients 3

Gynecological Mimics (in Females)

• Ovarian torsion is a surgical emergency that presents with acute right lower quadrant pain and requires urgent intervention to prevent ovarian loss 1
• Ruptured ovarian cyst causes sudden-onset right lower quadrant pain with peritoneal signs 3
• Pelvic inflammatory disease presents with bilateral or unilateral lower abdominal pain, fever, and elevated inflammatory markers 3
• Ectopic pregnancy must be excluded in all females of reproductive age presenting with right lower quadrant pain, as it is life-threatening 3
• Tubo-ovarian abscess can mimic complicated appendicitis with fever, leukocytosis, and right lower quadrant tenderness 3

Urological Mimics

• Ureterolithiasis (kidney stones) causes colicky flank pain that can radiate to the right lower quadrant, often with hematuria 3
• Pyelonephritis presents with fever, flank pain, and costovertebral angle tenderness that may be confused with retrocecal appendicitis 3
• Urinary tract infection can cause lower abdominal pain, though typically with dysuria and urinary frequency 4

Musculoskeletal and Neurological Mimics

• Psoas abscess presents with right lower quadrant pain, hip flexion weakness, and pain radiating to the groin or anterior thigh—the presence of true weakness distinguishes this from uncomplicated appendicitis 5
• Lumbar radiculopathy from disc herniation causes pain radiating down the leg with associated weakness in hip flexion, knee extension, or ankle dorsiflexion/plantarflexion 5
• Rectus sheath hematoma can occur after trauma or in patients on anticoagulation, presenting with focal abdominal wall pain 3

Vascular Causes

• Omental infarction presents with acute abdominal pain and can mimic appendicitis on clinical examination 3
• Mesenteric ischemia should be considered in patients with vascular risk factors presenting with severe pain out of proportion to examination findings 3

Critical Diagnostic Approach

When to Suspect Alternative Diagnoses

• Radiation of pain down the leg with weakness indicates nerve root involvement rather than visceral pathology and requires MRI lumbar spine if CT abdomen/pelvis is negative 5
• Bilateral lower abdominal pain or vaginal discharge suggests gynecological pathology over appendicitis 3
• Hematuria points toward urological causes 3
• Abdominal wall tenderness that increases with tensing abdominal muscles suggests musculoskeletal rather than intra-abdominal pathology 3

Imaging Strategy

• CT abdomen and pelvis with IV contrast has 97% sensitivity and 94% specificity for appendicitis in adults, but simultaneously evaluates for alternative diagnoses 6
• Ultrasound is useful in adolescents and females to evaluate gynecological causes, with 99% sensitivity when definitive results are obtained 6
• MRI should be obtained urgently if neurological examination suggests radiculopathy or if CT is negative but symptoms persist 5

Common Pitfalls to Avoid

• Do not assume right lower quadrant pain is appendicitis without considering the full differential, especially in females of reproductive age where gynecological causes are equally common 3
• Do not dismiss radicular symptoms or true weakness as simple appendicitis—these indicate neurological compromise requiring different imaging and management 5
• Do not rely on laboratory values alone—leukocytosis and elevated CRP occur in many inflammatory conditions beyond appendicitis 7, 4
• Do not delay surgical consultation in high-risk patients while pursuing extensive workup, as perforation risk increases with prolonged symptom duration 4