This is an example of a pathology proven epidermoid cyst with a classic onion ring appearance that corresponds to alternating layers of compacted keratin and loosely dispersed desquamated sqamous cells. This appearance, while very suggestive of an epidermoid cyst, has also rarely been described in cases of teratoma. Thus, negative laboratory testing of the tumor markers would increase confidence in the diagnosis.
Epidermoid cyst of the testes was first described in 1942 by Dockerty and Periestley as "undoubtedly benign, pure epidermoid cyst completely encased within the body of an otherwise normal testis." The tumor frequently occurs in the second to fourth decades of life and presents as a firm, well circumscribed, non-tender, intratesticular mass. Epidermoid cysts are discrete isolated tumors lying beneath the tunica albuginea. Typically epidermoid cysts range in size from 1-3 cm. There are several different theories about the embryologic origin of this lesion, however, the prevailing thought is that it represents monodermal development of a teratoma.
In 1969 Price set forth the following guidelines for identifying an intratesticular lesion as an epidermoid cyst:
- (a) The lesion must be an intraparenchymal cyst
- (b) The lumen must contain keratin
- (c) The cyst wall should contain fibrous tissue with a complete or incomplete inner lining of squamous epithelium
- (d) The cyst must contain no teratomatous components (eg, sebaceous glands, hair)
- (e) No scar may be seen in the remaining testicular parenchyma
Of benign testicular tumors, epidermoid cysts are the most common, however, they account for only 1-2% of all resected testicular masses. There is a slightly higher prevalence in the right testis and there are several reports or multiple cysts and bilateral cysts. Patients with multiple cysts have included one with Gardner syndrome, two with Klinefelter syndrome and one with a microscopic focus of primary carcinoid tumor in the cyst wall. Ocasionally, multiple cysts are also found in cryptorchid testes.
Ultrasound is the predominant means of analysis of testicular tumors, however, MRI has also been used. There are four main types of epidermoid cysts that vary in their ultrasound features due to variations in maturation, compactness, and quantitiy of keratin within the cyst. On color Doppler there is classically no internal flow in the lesion. The classification system that has been described in the literature is as follows:
- Type 1 – Classic Onion ring appearance
- Type 2 – Densely calcified mass with no cyst seen
- Type 3 – Cyst with a rim and either peripheral or central calcification
- Type 4 – A mixed pattern with a more heterogenous
On MRI a peripheral rim with low signal intensity on both T1- and T2-weighted images has been described with a circumferential zone of higher signal intensity surrounding a low-signal-intensity central zone. Also described are alternating concentric rings of low and high signal intensity on T1- and T2-weighted images. The central echogenic center seen at US corresponds to the lower-signal intensity zone seen at MR imaging and is thought to represent keratin debris. Likewise, the hypoechogenicity or alternating echogenicity seen at US corresponds to the surrounding higher signal intensity seen at MR imaging and represents the lipid- and water-containing material of the cyst. The squamous cell–lined capsule creates a hyperechogenic rim at US and a low-signal-intensity rim at MR imaging. No contrast material enhancement has been demonstrated at MR imaging, nor has the lesion been shown to be vascular on US.
Treatment for epidermoid cysts is still somewhat controversial and includes enucleation and orchiectomy. Is has been reported that if there is a high likelihood of a benign process and in cases of bilateral epidermoids, testicular sparing surgery can be attempted with a high probability of success; however, radical orchiectomy should still be the standard for solid masses and suspicious tumors.
Nathaniel Charter, M.D.
University of Pittsburgh School of Medicine
Department of Radiology