Torsion of the appendix testis

Last revised by Kieran Kusel on 3 Jan 2024

Torsion of the appendix testis (occasionally called torsion of the hydatid of Morgagni) is the most common cause of an acute painful hemiscrotum in a child. The appendix testis is located at the upper pole of the testis (between the testis and the head of the epididymis).

The normal appendix testis is 1 to 4 mm in length, and it is oval or pedunculated in shape.

The clinical presentation is with acute scrotal pain. The blue dot sign is a classic finding on physical examination which may be present. It describes a small firm nodule palpable at the superior aspect of the testis with bluish discoloration through the overlying skin.

Appendix testis is increased in size with an increase or decrease in echogenicity. Torsion of the appendix testis is frequently accompanied by a hydrocele and scrotal wall thickening 3.

A spherical shape and size of 6 mm with no internal vascularity and peripheral vascularity on Doppler scan are highly suggestive of torsion.

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