Capsule Summary
What is already known
Ultrasound is commonly used to detect ascites, and fluid tends to accumulate first in gravity-dependent areas such as Morison pouch and Douglas pouch.
What is new in the current study
This case highlights that a large renal cyst can mimic ascites on ultrasound, and the absence of fluid in gravity-dependent areas may help differentiate cystic lesions from true ascites.
A woman in her 80s presented to a local urology clinic with nausea and fever lasting for 2 days. She had a history of recurrent urinary tract infections and had previously undergone an abdominal ultrasound scan but not computed tomography (CT) imaging. At presentation, she did not report respiratory symptoms. The initial ultrasound performed at the clinic showed a large hypoechoic area interpreted as ascites (
Fig. 1A,
B). She was referred to our emergency department for further evaluation of possible gynecological or gastrointestinal disease.
At our hospital, a repeat ultrasound revealed the hypoechoic area around the right kidney but no fluid in Morison pouch or Douglas pouch, the key gravity-dependent spaces where ascitic fluid typically accumulates first (
Fig. 1C) [
1]. These spaces, located between the liver and right kidney (Morison pouch) and posterior to the uterus in females (Douglas pouch), allow even small amounts of free fluid to be detected in the supine position. The patient was evaluated in the supine position during both examinations. CT revealed multiple renal cysts in the right kidney, including a large cyst mimicking ascites (
Fig. 1D). No cystic lesions were seen in the liver or ovaries. CT also showed pneumonia around a hiatal hernia, which was determined to be the cause of the fever. This case illustrates a diagnostic pitfall in emergency ultrasound. Careful evaluation of gravity-dependent areas is essential when ascites is suspected [
2,
3]. The absence of fluid in these regions should prompt reconsideration and further imaging, as cystic structures may appear as free fluid.
NOTES
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Ethics statement
Written informed consent for publication of the research details and clinical images was obtained from the patient. This study did not require institutional review board approval, as it is a single-case report that does not include identifiable personal data.
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Author contributions
Conceptualization: RI; Investigation: all authors; Supervision: MO, TI; Visualization: RI; Writing–original draft: RI; Writing–review & editing: all authors. All authors read and approved the final manuscript.
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Conflicts of interest
The authors have no conflicts of interest to declare.
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Funding
The authors received no financial support for this study.
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Acknowledgments
The authors would like to thank the patient for providing consent to share this case and the emergency department staff at Toho University Sakura Medical Center for their support in the clinical management and imaging evaluation of the patient.
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Data availability
Data sharing is not applicable as no new data were created or analyzed in this study.
Fig. 1.Ultrasound and computed tomography (CT) findings in a case of a giant renal cyst mimicking ascites. (A, B) Initial abdominal ultrasound image showing a hypoechoic area in the upper abdomen, which was misinterpreted as a large volume of ascites at a local clinic (arrows). (C) Focused ultrasound image of Morison pouch performed at our hospital, showing no fluid collection in this gravity-dependent area, suggesting that ascites was unlikely (arrow). (D) Coronal abdominal CT image revealing multiple renal cysts, including a large right renal cyst that accounted for the misleading ultrasound appearance (arrow). No cystic lesions were seen in the liver or ovaries. The arrows indicate the large renal cyst misinterpreted as ascitic fluid.
REFERENCES
- 1. Kaur G, Kaur T, Das CJ. Morrison's pouch: anatomy and radiological appearance of pathological processes. Indian J Radiol Imaging 2023;33:80-8.
- 2. Goldberg BB, Goodman GA, Clearfield HR. Evaluation of ascites by ultrasound. Radiology 1970;96:15-22.
- 3. Forsby J, Henriksson L. Detectability of intraperitoneal fluid by ultrasonography: an experimental investigation. Acta Radiol Diagn (Stockh) 1984;25:375-8.
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