Most Likely Diagnosis: Acute Cholecystitis
The most likely diagnosis is C. Acute cholecystitis, despite the absence of fever and leukocytosis, given the clinical presentation of RUQ pain, vomiting, and distended gallbladder with multiple gallstones.
Clinical Reasoning
Why Acute Cholecystitis Remains the Primary Diagnosis
Acute cholecystitis does not always present with classic inflammatory markers. A 2023 case report documented acute cholecystitis with normal WBC count, no fever, and negative Murphy's sign, yet intraoperative findings revealed a very distended, inflamed, and edematous gallbladder 1.
The distended gallbladder with multiple gallstones in the setting of acute RUQ pain and vomiting is highly suggestive of cystic duct obstruction, the primary pathogenic mechanism of acute cholecystitis 2, 1.
Ultrasound findings can be equivocal in acute cholecystitis. The ACR guidelines note that the gallbladder may appear contracted or distended, and pericholecystic fluid is variably present 2, 3. The absence of wall thickening does not exclude acute cholecystitis, particularly in early presentations 1.
Why Other Diagnoses Are Less Likely
Gallbladder Empyema (Option B):
- Empyema represents a complication of acute cholecystitis with purulent material in the gallbladder 2.
- This typically presents with more severe systemic signs including fever and marked leukocytosis, which are absent in this patient 2.
- Empyema is not a primary diagnosis but rather a progression of untreated acute cholecystitis.
Pancreatitis (Option A):
- While the obscured CBD raises concern for biliary pancreatitis, the primary symptom localization is RUQ rather than epigastric 4.
- The ultrasound findings focus on gallbladder pathology rather than pancreatic inflammation.
- Serum lipase/amylase levels (not mentioned) would be critical to evaluate this diagnosis.
Gallbladder Mucocele (Option D):
- Mucocele typically presents with chronic, intermittent symptoms rather than acute 12-hour onset 5.
- While a distended gallbladder can represent mucocele, the acute presentation with vomiting favors acute inflammatory process 5.
- Mucocele is more commonly an incidental or chronic finding requiring MRCP for definitive diagnosis 5.
Recommended Diagnostic Approach
Immediate Next Steps
Hepatobiliary scintigraphy (HIDA scan) should be performed if clinical suspicion remains high despite equivocal ultrasound findings. HIDA scan has 97% sensitivity and 90% specificity for acute cholecystitis, superior to ultrasound's 88% sensitivity and 80% specificity 2.
The absence of gallbladder visualization on HIDA scan confirms cystic duct obstruction, the hallmark of acute cholecystitis, even when inflammatory markers are absent 1, 6.
Important Clinical Pitfalls
Do not exclude acute cholecystitis based solely on absent fever or normal WBC count. Up to one-third of acute cholecystitis cases may present atypically 1, 4.
The sonographic Murphy sign has relatively low specificity and its absence is unreliable, particularly if the patient received pain medication prior to imaging 2.
Thin-walled or non-thickened gallbladder does not exclude acute cholecystitis, especially in early disease or when imaging is performed shortly after symptom onset 1.
If HIDA Scan Is Unavailable or Contraindicated
CT abdomen with IV contrast can identify complications of acute cholecystitis including gangrene, perforation, or adjacent liver parenchymal hyperemia 2.
MRCP with contrast-enhanced MRI provides comprehensive evaluation and can distinguish acute from chronic cholecystitis based on T2 signal characteristics and wall enhancement patterns 2.
Management Implications
Early surgical consultation is warranted given the acute presentation, as laparoscopic cholecystectomy is the treatment of choice for uncomplicated acute cholecystitis 7. The 12-hour symptom duration places this patient in the optimal window for early cholecystectomy, which reduces complications and hospital stay 2.