A 48-year-old man with acute acalculous cholecystitis (confirmed on ultrasound: thickened wall, pericholecystic fluid, no stones) is being compared with a 55-year-old woman with acute calculous cholecystitis (impacted stone, similar imaging findings). Which feature most reliably distinguishes acalculous from calculous acute cholecystitis?

Explanation

## Acalculous vs. Calculous Acute Cholecystitis: The Discriminator ### Definitional Distinction **Key Point:** The defining feature of acalculous cholecystitis is the **absence of gallstones** on imaging (ultrasound, CT, or HIDA scan). Calculous cholecystitis requires a stone impacting the cystic duct. ### Comparison Table | Feature | Acalculous Cholecystitis | Calculous Cholecystitis | | --- | --- | --- | | **Gallstones** | Absent | Present (required) | | **Pathophysiology** | Bile stasis, ischemia, chemical irritation, bacterial overgrowth | Stone impaction + inflammation | | **Incidence** | 5–10% of acute cholecystitis | 90–95% of acute cholecystitis | | **Risk factors** | Critical illness, sepsis, prolonged fasting, TPN, trauma | Obesity, female, forty, fat, fertile | | **Fever/WBC** | Often higher (more septic) | Moderate elevation | | **Mortality** | 10–30% (higher) | 1–3% (lower) | | **Imaging finding** | Thickened wall, pericholecystic fluid, NO stone | Thickened wall, pericholecystic fluid, stone present | ### Why Presence/Absence of Stones Is the Discriminator **High-Yield:** By definition, acalculous cholecystitis occurs **without gallstones**. This is not a clinical judgment call — it is a diagnostic criterion. Imaging (ultrasound or CT) directly answers the question: are stones present or absent? **Clinical Pearl:** Acalculous cholecystitis is a diagnosis of exclusion in the setting of acute cholecystitis findings WITHOUT stones. It is more common in critically ill, septic, or post-operative patients and carries higher morbidity and mortality. ### Why Other Options Do Not Discriminate 1. **Severity of systemic inflammation** — Acalculous cholecystitis is often *more* inflammatory and septic, but both can present with fever and leukocytosis. Overlap is substantial; severity does not reliably separate them. 2. **Positive Murphy's sign** — Both acalculous and calculous cholecystitis can present with positive Murphy's sign; this is not a discriminator. 3. **Gallbladder wall thickening** — Both conditions cause wall thickening (>3 mm) and pericholecystic fluid; these findings are identical. **Mnemonic:** **STONE** — **S**tone **T**here = calculous; **O**bstruction **N**ot from **E**xternal stone = acalculous. [cite:Sabiston Textbook of Surgery 21e Ch 54]