SONOWORLD : Epidermoid cyst of the testicle
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Epidermoid cyst of the testicle
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Presentation A 19 year old male presented with a unilateral non tender testicular mass. The patient gives a history of gradual increase in size of the mass. A scrotal ultrasound was performed.
Caption: Transverse image of left scrotum.
Description: An intratesticular mass is seen in the upper pole of the left testis. The mass exhibits a heterogeneous internal echo pattern characterized by rings of increased and decreased echogenicity. Through transmission of sound is markedly increased.
Caption: Transverse color Doppler image
Description: The testicular mass shows only minimal blood flow.
Differential Diagnosis Testicular Neoplasm, Epidermoid Cyst.
Final Diagnosis Epidermoid Cyst of the Testicle.

Epidermoid inclusion cysts of the testis are uncommon benign testicular tumors. They account for approximately 1% of all testicular tumors, and fewer than 200 cases have been reported.. Although patients as young as 3 years old and as old as 77 years old may have epidermoid inclusion cysts, the tumors most often occur in men 20-40 years old. More than 80% of the lesions are painless. The size varies from 1 to 3 cm, and the right testis is involved slightly more often than the left (54% vs. 46%).

Although various theories of histogenesis have been postulated, including squamous metaplasia of rete testis, squamous metaplasia of the seminiferous epithelium, and inclusion of epidermoid cysts, the prevailing hypothesis is that of germ cell origin (the tumors develop along the line of epidermal differentiation as a monodermal expression of a teratoma).
Pathologically, the lesion is cystic and is contained within the testis. The lumen contains keratin but no teratogenous elements or dermal adnexal structures such as sebaceous glands or hair follicles. The wall of the cyst is composed of fibrous tissue with a complete or incomplete inner lining of squamous epithelium.

Clinical presentation: A firm, smooth, nontender mass is usually discovered incidentally by the patient or during routine physical examination.

Imaging: The sonographic characteristics are variable. 
Ultrasound may show either-
1. A mass with a "target" appearance (a central area of increased echogenicity surrounded by a sonolucent zone), or
2. A sharply defined mass with hyperechoic margins representing a rim of calcifications, or
3. A well-defined, solid mass with an echogenic rim and high-intensity echoes throughout.
MRI: The epidermoid cyst produces a classical"bull`s-eye" pattern on MR images, in which a difference in MR signal intensity is caused by various tissue components present in the epidermoid cyst.

Differential diagnosis: Testicular malignant tumors are most often single and present as a hypoechoic mass. Rarely, they manifest as echogenic or complex masses. The tunica albuginea may be invaded and there may be distortion of the testicular contour.
In the current case of testicular epidermoid cyst the alternating rings of hyper and hypoechogenicity correlate well with the alternating layers of epithelial tissue, adjacent compacted keratin, and loosely dispersed squamous cells.

Management: Epidermoid cysts of the testes have a benign course, with no local or metastatic recurrence for periods of 6 months to 15 years. Therefore, conservative management (i.e. enucleation with testicular preservation) may be the preferable alternative in those patients in whom characteristic clinical, laboratory, and sonographic criteria are met. In sonographic imaging of these lesions, the "onion ring" configuration is such a characteristic finding.

Case References

1. Shah KH, Maxted WC, Chun B. Epidermoid cysts of the testis: a report of three cases and an analysis of 141 cases from the world literature. Cancer 1981;47:577-582.
2. Cotter M, Lampert IA, Salm R. Epidermoid cysts of the testicle. Clin Oncol 1984;10:149-154.
3. Malek RS, Rosen JS, Farrow GM. Epidermoid cysts of the testicle: a critical analysis. Br J Urol 1986;58:55-59.
4. Price EB Jr. Epidermoid cysts of the testis: a clinical and pathological analysis in 69 cases from the Testicular Tumor Registry. J Urol 1969;102:708-713.
5. Maxwell AJ, Mamtora H. Sonographic appearance of epidermoid cyst of the testis. J Clin Ultrasound 1990;18:188-190.
6. Bahnson RR, Slasky BS, Ernstoff MC, Banner BF. Sonographic characteristics of epidermoid cysts of testicle. Urology 1990;35:508-510.

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