Saturday, February 16, 2008

Horse or Zebra?

Every clinician is eventually called on to evaluate a possible inguinal hernia. When confronted with a common clinical problem, it's easy to assume that it is yet another case of something you have seen a thousand times before. As we learned in medical school, "When you hear hoofbeats, think horses, not zebras".

Unfortunately, this is walking down the garden path. Every once in a while, the hoofbeats turn out to be a zebra!

Twenty-nine year-old male presented with an inguinal mass, suspected to be a hernia by the surgeon. The mass looked "odd" on an ultrasound and the patient had a follow-up MRI.

(A) Coronal T1-weighted image shows a predominantly fat signal mass (red arrows) occupying the right inguinal canal, and extending into the scrotum. (B) The mass (white arrow) is dark on a STIR image, confirming that it is primarily fatty in nature.

Axial T1-weighted image shows the mass (red arrows) in the scrotum, adjacent to a normal testicle (green arrow):

It's easy to call this an inguinal hernia, but there is absolutely no bowel in the mass. This is an example of a scrotal lipoma.

The earliest publication I can find is from 1925, when surgeon G. Paul LaRoque of Richmond, Virginia described this entity.

(click on image to enlarge)

I have seen two of these lesions in the last three years, and my practice is largely musculoskeletal radiology. These lesions, while rare, should be in the differential diagnosis when you are assessing an inguinal or scrotal mass, especially on ultrasound. 

Vic David MD

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