A testicular appendix (alternatively called appendix of testis or appendix testis, and historically also known as hydatid of Morgagni) represents a developmental remnant of the paramesonephric duct (Müllerian duct) which is situated in the upper pole of the testis inside a groove between the testis and the head of epididymis ¹.

Epidemiology

The prevalence in childhood is around 85% (range 83-92%). The testicular appendix can be bilateral in 69% of the cases ⁴.

Clinical presentation

Testicular appendages in general alone have no clinical significance. However, when complicated by torsion, they can lead to acute scrotal pain ².

Radiographic features

Ultrasound

Ultrasonography with high-frequency linear array transducers is the modality of choice in evaluating the scrotum and testis with its appendages. It can quickly and easily demonstrate the existence of such anatomic structures and their vascularity without exposure to radiation.

Appendages of the testis are best seen when combined with hydrocele. The frequency of the ultrasonographic identification of these anatomic structures is around 89% ³.

The normal testicular appendix is seen as an oval, sessile structure in 88% of cases ⁴. Its length ranges from 1 to 7 mm ¹. Color Doppler ultrasonography can occasionally detect blood flow inside testicular appendages ⁴. When pedunculated, the appendix is in danger of torsion.

History and etymology

"Appendix testis" was first described by Giovanni Battista Morgagni (1682-1771) in his textbook 'De Sedibus et Causis Morborum per Anatomen Indagatis' (On the Seats and Causes of Diseases Investigated by Anatomy) in 1761 ⁵.

Differential diagnosis

In cases of torsion, patients present with acute scrotal pain and imaging differential diagnosis includes:

• testicular torsion

• epididymo-orchitis

• acute idiopathic scrotal edema

• torsion of the epididymal appendix

Related pathology

• torsion of testicular appendix