mesothelial cyst pathology outlines

Definition / general
Benign, cystic lesions that may be confused with testicular tumors
Does not include cystic neoplasms (e.g., epidermoid cyst, dermoid cyst [teratoma], papillary cystadenoma of the epididymis)

Essential features
Mesothelial cysts and hydrocele constitute benign true cysts and fluid collections arising from the mesothelial lining of the visceral and parietal tunica vaginalis and are more common in children
Cysts and cystic dilatations of the epididymis and rete testis (or more rarely, the seminiferous tubule) arise from the tubal epithelium, frequently secondary to obstruction and are more common in adults
Frequently characterized by simple unilocular or multilocular cystic structures and an absence of complex growth / solid areas

Includes true cysts and fluid collections (celes) of the spermatic cord and paratesticular structures
2 main types
Extratesticular (arises from the mesothelial lining [tunica vaginalis] and does not communicate with tubular system)

Encysted presentation does not communicate with peritoneal cavity
Funicular presentation does communicate with peritoneal cavity
Mesothelial cyst (also termed spermatic cord cyst)
Testicular (arises from the epithelial lining of the rete testis, efferent ducts and epididymis)
Epididymal cysts and cystic dilatation (tubular ectasia) of epididymis and rete testis are associated and likely exist on a continuum
Epididymal cysts > 2 cm within the vaginal cavity are termed spermatocele
Cystic dysplasia of rete testis is distinctive congenital malformation
ICD coding
N50.3 - cyst of epididymis
N50.89 - other specified disorders of the male genital organs
N50.81 - testicular pain
N50.811 - right testicular pain
N50.812 - left testicular pain
N50.819 - testicular pain, unspecified
N50.82 - scrotal pain
N50.9 - disorder of male genital organs, unspecified

Hydrocele is one of the most common causes of painless scrotal swelling in infants (up to 10%); generally regresses spontaneously by 1 - 2 years old and rarely persists into adulthood
Mesothelial cysts are most common in men > 40 years old
Cysts and cystic dilatation of epididymis and rete testis constitute the most common paratesticular cystic lesions, frequently in men > 55 years old and seen in up to 30% of asymptomatic patients at ultrasound (AJR Am J Roentgenol 1984;143:161)
Cystic dysplasia of rete testis is rare, generally unilateral and most often seen in children (mean presentation of 5 years old), in association with urinary tract malformations (Front Pediatr 

Spermatic cord, testicular adnexa

Congenital form occurs due to patent processus vaginalis or abnormal closure of processus; most regress by adulthood
May be associated with trauma, testicular torsion, tumors, chronic inflammation (e.g., in setting of bacterial epidiymoorchitis, filarial disease) or congenital lymphatic malformations
Mesothelial cyst
Mesothelial rests trapped during embryonic development (J Urol 1975;114:730)
Cysts (and cystic dilatation) of epididymis and rete testis
Acquired condition frequently associated with or resulting from mechanical compression of epididymis or spermatic cord by surgical changes (e.g., vasectomy), trauma, neoplastic or infectious process, dialysis (rete testis cystic dilation) or hormonally induced atrophy of epididymis (e.g., secondary to cirrhosis) (Hum Pathol 1996;27:336, Am J Surg Pathol 1996;20:1231, J Ultrasound 2011;14:208)
Rare intraparenchymal cystic dilatation of seminiferous tubules may result from focal malformation or inflammation

cysts associated with in utero exposure to diethylstilbestrol
Cystic dysplasia of rete testis
Congenital malformation of rete testis, frequently associated with ipsilateral urogenital malformations (e.g., renal agenesis, multicystic dysplasia of the kidney)
Thought to arise due to disorders of communication between mesonephric duct and germinal epithelium during development (Front Pediatr 2022;10:898038)
Clinical features
Painful or painless cystic swelling of the scrotum
May be incidentally identified

Ultrasonography (Doppler ultrasonography is important in a setting of painful swelling to rule out testicular torsion)
Radiology description
Varies by entity
Most frequently characterized by simple uninoculated or multiloculated fluid filled cystic structures
Complex loculations or areas of solid growth should raise concern for alternative etiology


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