Radiological Category Genitourinary Principal Modality 1 Ultrasound Principal

Case History • • ER patient with right flank pain, suspect kidney stones. Negative

Test Your Diagnosis Which one of the following is your choice for the appropriate

Findings and Differentials Findings: - Bilaterally symmetric hypoechoic perirenal areas, paralleling the renal contour

Discussion Ultrasound of the kidneys demonstrate bilateral avascular hypoechoic areas with multiple septations, these

Discussion Septated hypoechoic perirenal fat is a rare but recognized pitfall in renal ultrasound

Diagnosis Septated hypoechoic perirenal fat – a normal variant.

References Septated hypoechoic perirenal fat on sonograms: a pitfall in renal ultrasonography, H. M.

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Radiological Category: Genitourinary Principal Modality (1): Ultrasound Principal Modality (2): General radiography Case Report #0607 Submitted by: Andrew Baugh, M. D. Faculty reviewer: Verghese George, M. D. Date accepted: 15 March 2009

Case History • • ER patient with right flank pain, suspect kidney stones. Negative blood and urine exam.

Radiological Presentations

Test Your Diagnosis Which one of the following is your choice for the appropriate diagnosis? After your selection, go to next page. • Perirenal abscesses • Perirenal effusions • Perirenal fat • Perirenal hematomas

Findings and Differentials Findings: - Bilaterally symmetric hypoechoic perirenal areas, paralleling the renal contour - Multiple septations - Avascular Differentials: • Perirenal Abscess • Perirenal Effusions • Hypoechoic perirenal fat • Perirenal Hematomas

Discussion Ultrasound of the kidneys demonstrate bilateral avascular hypoechoic areas with multiple septations, these do not cause mass effect on the kidneys.

Discussion Septated hypoechoic perirenal fat is a rare but recognized pitfall in renal ultrasound imaging. Although fat is typically hyperechoic on ultrasound, it can show hypoechoic appearances in certain areas, breast being the characteristic example. Perinephric fat can appear hypoechoic; the septations are normally present in the perinephric spaces and appear pronounced when contrasted against the hypoechoic fat. Bilaterally symmetric appearance, lack of flow on Doppler and absence of history to support a competing diagnosis is sufficient to make this diagnosis. However, a CT scan be used to differentiate when there is enough uncertainty to justify further imaging. In this case, there was no reason to suspect another cause, and a confirmatory CT was not performed.

Diagnosis Septated hypoechoic perirenal fat – a normal variant.

References Septated hypoechoic perirenal fat on sonograms: a pitfall in renal ultrasonography, H. M. Brammer, W. S. Smith, and P. R. Lubbers, J. Ultrasound Med. , Vol. 11, Issue 7, 361 -363, July 1, 1992 Diagnostic Ultrasound Mc. Gahan, J and Goldberg, B (2008) 2 nd edition 838 Hypoechoic Fat: A Sonographic Pitfall Spencer G et al AJR (1995) 164 1277 -1280