The appendix testis (or hydatid of Morgagni) is a vestigial remnant of the Müllerian duct, present on the upper pole of the testis and attached to the tunica vaginalis.

[citation needed] The appendix of testis can occasionally become twisted, causing acute one-sided testicular pain and may require surgical excision to achieve relief.

One third of patients present with a palpable "blue dot" discoloration on the scrotum.

If clinical suspicion is high for the serious differential diagnosis of testicular torsion, a surgical exploration of the scrotum is warranted.

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