Definition
A benign tumour of mesothelial cells characterized by numerous gland-like spaces, tubules or cords.
Synonym
Benign mesothelioma.
Incidence
Adenomatoid tumours are the most common tumours of the testicular adnexa, representing 32% of all tumours in this
location and 60% of all benign neoplasms in this area.
Clinical features
Signs and symptoms
These begin to appear in the late teens and up to 79 years and most are seen in the third through the fifth decades (mean age 36 years). They present as small, solid intrascrotal tumours, and are usually asymptomatic. They have typically been present for several years without appreciable growth and are uniformly benign.
Imaging
Adenomatoid tumours are smooth, round, and well circumscribed masses of variable size generally arising in the epididymis. They are typically described as hyperechoic and homogeneous. This should not, however, be considered
characteristic as great variability has been reported. The most important point is to clearly identify the mass as extratesticular and if it can be shown to be arising from the epididymis, adenomatoid tumour is the most likely
diagnosis. They may also arise from the spermatic cord and tunica albuginea, where they can grow intratesticularly. The latter presentation is indistinguishable from testicular germ cell neoplasms.
Localization
Most of these occur in or near the lower pole or upper pole of the epididymis but other sites include the body of the epididymis, the tunica vaginalis, tunica albuginea and rete testis. Rarely the parietal tunica or spermatic cord may be
involved.
Macroscopy and histopathology
These are usually small tumours, 2.0 cm or less, but they have ranged from 0.4 to 5.0 cm. They are round or oval
and well circumscribed although they can also be flattened and plaque-like.
Microscopically these consist of eosinophilic mesothelial cells forming solid cords as well as dilated tubules with
flattened lining cells which may initially suggest an endothelial appearance. Vacuolated cytoplasm is a prominent feature of the cells. The stroma is usually fibrous but may consist largely of smooth muscle.
Ultrastructural and immunohistochemical features of these tumours support their mesothelial cell origin. There is an
absence of epithelial/carcinoma markers MOC-31, Ber-Ep4, CEA, B72.3, LEA 135 and Leu M1 and also factor VIII and CD34. They invariably express cytokeratins AE1/AE3 and EMA. |
