Torsion of the appendix testis

Last revised by Dr Jeremy Jones on 20 Sep 2021

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.

Blue dot sign:

  • classic finding on physical examination
  • small firm nodule is palpable on the superior aspect of the testis and exhibits 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 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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Cases and figures

  • Case 1
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  • Case 2
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