Applied Radiology

Diagnosis

Findings

The sonogram of the left testis revealed a heterogeneous, well-circumscribed intratesticular mass, composed of mixed hypoechoic and hyperechoic components with discontinuous curvilinear, somewhat concentric, highly reflective echoes. Small focal punctate echogenicities were also noted. The mass measured 2.9 * 2.6 * 2.9 cm and was avascular.

Discussion

Testicular epidermoid cysts are classified as benign germ cell tumors that comprise approximately 1% to 2% of all resected testicular masses.^1,2 They are found most commonly in males in their second through fourth decades of life.^1,3 A typical presentation is a painless testicular nodule incidentally discovered during physical examination.^1,4 Alternatively, diffuse testicular enlargement is noticed in approximately 10% of cases.^1,5 These presenting symptoms overlap with those of malignant testicular neoplasms.

At pathological examination, testicular epidermoid cysts are well-circumscribed solid masses, confined by the tunica albuginea. The lesions are encapsulated by a fibrous wall containing an inner layer of squamous epithelium.⁶ This fibrous wall often becomes calcified, and sometimes, even ossified.⁴ Within the center of the cyst is thick, pasty squamous epithelium and keratin debris.

The classification of testicular epidermoid cysts within other categories of testicular lesions is controversial. Many believe a testicular epidermoid cyst to be the end result of a teratoma that has undergone monodermal or monomorphic differentiation, as it contains only the epidermal portion of ectoderm.^1,4,5 However, testicular epidermoid cysts exhibit no malignant potential, as testicular intraepithelial neoplasia, a histologic precursor for germ cell tumors, is absent. This has called into question the germ cell origin of epidermoid cysts.⁷ Currently, the World Health Organization classifies testicular epidermoid cysts as "tumor-like lesions."⁷

Long-term follow-up has been possible in several series of patients who have undergone testis-sparing surgery. After resection of testicular epidermoid cysts, patients have remained disease-free for up to 23 years post-surgery with neither local recurrence nor distant metastases.^1,4,7,8 While definitive diagnosis requires histologic examination, suggestive preoperative imaging findings of an epidermoid cyst can prepare the surgeon and the patient for a testis-sparing enucleation of the mass. This more conservative approach, with intraoperative frozen-section histologic analysis, can prevent unnecessary radical orchiectomy.⁹

The key to utilizing this approach, therefore, lies in the preoperative imaging findings. The testicular epidermoid cyst may have a variable sonographic appearance, but some features suggestive of the histologic diagnosis have been identified.⁹ Testicular epidermoid cysts are generally well defined sonographically, with a hyperechoic rim cor-responding to the dense fibrous capsule. If any calcification of the capsule has occurred, it will exhibit the typical hyperechogenicity with acoustic shadowing. Concentric rings of alternating hypo- and hyperechogenicity within the cyst (the so-called "onion-ring" appearance) correspond to the histologic finding of alternating layers of compacted keratin and loosely arranged desquamated squamous cells.⁷ Within the lesion, an echogenic focus may have formed as the innermost keratinized debris became compacted centrally, producing a "target" or "bull's-eye" appearance.¹⁰ These characteristic sonographic features should alert the radiologist to the benign nature of these masses. In this case, sonographic findings were not classic and the mass was thought to be a malignant germ cell tumor. Although any solid intratesticular mass should be considered to be a neoplasm until proven otherwise, the radiologist should seek a target sign or curvilinear calcification in a concentric configuration, even if the rings are incomplete. If found, the surgeon should be alerted to the possibility of an epidermoid cyst, which may permit an attempt at testis sparing enucleation rather than a radical orchiectomy.

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 47:577-582, 1981.

2. Price AB Jr: Epidermoid cyst of the testis: A clinical and pathological analysis of 69 cases from the testicular tumor registry. J Urol 102:708-713, 1969.

3. Caravelli JF, Peters BE: Sonography of bilateral testicular epidermoid cysts. J Ultrasound Med 3:273-274, 1984.

4. Malek RS, Rosen JS, Farrow GM: Epidermoid cyst of the testis: A critical analysis. Br J Urol 58:55-59, 1986.

5. Buckspan MB, Skeldon SC, Klotz PG, et al: Epidermoid cysts of the testicle. J Urol 134:960-961, 1985.

6. Dambro TJ, Stewart RR, Carroll BA: The scrotum. In: Rumack CM, Wilson SR, Charbonneau JW (eds): Diagnostic Ultrasound. pp. 791-821. St. Louis, Mosby, 1998.

7. Dieckmann KP, Loy V: Epidermoid cyst of the testis: A review of the clinical and histogenetic considerations. Br J Urol 73:436-441, 1994.

8. Ross JH, Kay R, Elder J: Testis sparing surgery for pediatric epidermoid cysts of the testis. J Urol 149:353-356, 1993.

9. Langer JE, Ramchandani P, Siegelman ES, Banner MP: Epidermoid cysts of the testicle: Sonographic and MR imaging features. AJR Am J Roentgenol 173:1295-1299, 1999.

10. Brenner J, Cumming WA, Ros PR: Testicular epidermoid cyst: Sonographic and MR findings. AJR Am J Roentgenol 152:1344, 1989. Letter.