Monorchidism or unilateral anorchidism.

Unilateral anorchidism, or monorchidism, refers to the absence of one testis. It is defined as the unilateral or bilateral partial or complete absence of testicular tissue, with or without rudimentary epididymal and spermatic cord remnants, in the presence of internal Wolffian duct development and normal external genitalia. In the case of monorchidism with derivatives of the Wolffian duct an ipsilateral testis must be present at least up to the 16th week of gestation to induce the formation of an epididymal structure. Few studies have been devoted to the etiology of monorchidism or to management of the contralateral solitary testis. With the aid of a personal series of 36 cases and a review of the literature the etiopathology of monorchidism is discussed; the long-term fate of the contralateral testis is considered, and an answer to the question of whether protection of the solitary contralateral testis by orchidopexy is really indicated, as stated by most authors, is offered. Ischemia due to intrauterine torsion is thought to be the cause of monorchidism; it is thus a syndrome of testicular regression. The histopathological findings are characteristic, if not specific, for atrophy secondary to ischemia. Vas deferens, epididymis, calcification or hemosiderin pigmentation is noted in almost 90% of cases. In the absence of these remnants, clinical and surgical findings and the presence of a richly vascular stroma support the diagnosis. According to the author's experience, exploration and fixation of the contralateral testis is neither necessary nor desirable.