Testicular Epidermoid Cyst: Causes, Diagnosis, Imaging, Treatment, and Prognosis

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 Testicular Epidermoid Cyst: Causes, Diagnosis, Imaging, Treatment, and Prognosis

Introduction

Testicular epidermoid cysts (TECs) are rare, benign intratesticular lesions that can clinically and radiologically mimic malignant germ cell tumors. Despite their benign nature, accurate diagnosis is critical because radical orchiectomy is often performed due to diagnostic uncertainty. TECs account for approximately 1–2% of all testicular tumors and are composed entirely of keratinizing squamous epithelium without any dermal appendages. Their etiology remains controversial, but their characteristic imaging appearance—particularly on ultrasound—can aid in diagnosis and avoid unnecessary aggressive treatment.

1. Cause and Etiology

The exact cause of testicular epidermoid cysts is not fully understood. Two prevailing theories exist:

  1. Monodermal Teratoma Theory
    TECs may represent a monodermal variant of mature teratomas derived from germ cells that differentiate exclusively into keratinizing squamous epithelium.

  2. Epidermal Inclusion Theory
    TECs may arise from squamous metaplasia of the rete testis or from epidermal cells implanted during fetal development, trauma, or surgery.

Unlike malignant germ cell tumors, TECs are not associated with elevated serum tumor markers (AFP, β-hCG, LDH), which is a useful distinguishing point during diagnosis.

2. Pathophysiology

Histologically, a testicular epidermoid cyst is lined by keratinizing squamous epithelium and filled with concentric layers of keratin debris, giving rise to the "onion-skin" appearance on imaging. There is no evidence of skin appendages (sebaceous glands, hair follicles), which differentiates TECs from dermoid cysts.

The cyst grows slowly, exerting a mass effect within the testicular parenchyma. There is no invasion into surrounding tissues or metastatic potential.

3. Epidemiology

  • Incidence: 1–2% of all testicular masses.

  • Age group: Most common between the 2nd and 4th decades of life, though cases have been reported in children and older adults.

  • Laterality: Typically unilateral, with no significant predilection for left or right testis.

  • Malignant potential: None, provided the lesion is purely epidermoid with no associated germ cell tumor elements.

4. Clinical Presentation

Most patients present with a painless testicular mass discovered incidentally or during self-examination. Key features:

  • Duration: Slowly enlarging over months to years.

  • Pain: Rare, unless complicated by rupture or inflammation.

  • Physical Exam: Firm, well-circumscribed, non-tender intratesticular nodule.

  • Laboratory: Normal AFP, β-hCG, and LDH levels.

5. Imaging Features

5.1 Ultrasound (US)

Ultrasound is the gold standard for evaluating testicular masses.

Typical findings:

  • Well-circumscribed, avascular intratesticular lesion

  • Onion-skin appearance: Concentric alternating hyperechoic and hypoechoic rings representing layers of keratin.

  • Target sign: Hypoechoic rim with central hyperechoic focus.

  • Absence of internal vascularity on Doppler.

Figure 1: Ultrasound image showing classic onion-skin appearance of a testicular epidermoid cyst.


5.2 Magnetic Resonance Imaging (MRI)

MRI is not routinely required but can help in ambiguous cases.

  • T1-weighted: Variable signal intensity depending on keratin content.

  • T2-weighted: Low-to-intermediate signal.

  • No contrast enhancement within the cyst.

Figure 2: MR T1-weighted axial, T2-weighted axial, and post-contrast coronal images are displayed.

5.3 Computed Tomography (CT)

CT is rarely used for primary diagnosis but may be indicated to rule out metastases in atypical cases.

6. Treatment

6.1 Surgical Management

Historically, most TECs were treated with radical orchiectomy due to difficulty distinguishing them from malignant tumors. However, testis-sparing surgery (TSS) with intraoperative frozen section analysis is now favored when imaging and serum markers strongly suggest a benign lesion.

  • Radical Orchiectomy: Complete removal of the affected testis.

  • Enucleation: Removal of the cyst while preserving normal testicular tissue.

  • Intraoperative frozen section: Confirms benign nature and prevents overtreatment.

6.2 Indications for Testis-Sparing Surgery

  • Preoperative ultrasound features consistent with TEC.

  • Normal tumor markers.

  • Small, well-circumscribed lesion.

  • Patient preference for fertility preservation.

7. Prognosis

The prognosis for testicular epidermoid cysts is excellent following complete excision. Recurrence is extremely rare, and there is no risk of metastasis. Long-term follow-up typically shows normal testicular function in cases where testis-sparing surgery is performed.

8. Figure Captions

Figure 3: Scrotal ultrasound demonstrating a well-circumscribed, avascular intratesticular lesion with concentric hyperechoic and hypoechoic layers—characteristic "onion-skin" pattern of a testicular epidermoid cyst.

Figure 4: Doppler ultrasound showing absence of internal vascularity within the lesion, supporting the benign nature.

Figure 5: Histopathological image revealing a cyst lined by keratinizing squamous epithelium filled with laminated keratin debris, confirming the diagnosis.

Quiz

Q1. Which of the following tumor markers is typically elevated in testicular epidermoid cysts?
A. AFP
B. β-hCG
C. LDH
D. None of the above

Q2. The "onion-skin" pattern seen in ultrasound imaging of a testicular epidermoid cyst corresponds to:
A. Layers of calcification
B. Layers of keratin debris
C. Vascular septations
D. Fibrous tissue

Q3. What is the definitive diagnostic method for confirming a testicular epidermoid cyst?
A. Serum tumor markers
B. MRI
C. Histopathology
D. CT scan

Q4. Which of the following is TRUE regarding testicular epidermoid cysts?
A. They have malignant potential.
B. They usually present with elevated tumor markers.
C. They can be managed with testis-sparing surgery if benign features are present.
D. They are most common in patients over 60 years of age.

Answer & Explanation

1. Answer: D. Explanation: TECs do not elevate serum tumor markers, which helps differentiate them from malignant germ cell tumors.

2. Answer: B. Explanation: Concentric layers of keratin produce alternating echogenic and hypoechoic rings.

3. Answer: C. Explanation: Histopathological examination after surgical excision confirms the diagnosis.

4. Answer: C. Explanation: TECs are benign, marker-negative, and can be treated conservatively with testis-sparing surgery when criteria are met.

References

[1] S. C. Woodward, M. Schwab, and M. P. Rittenberg, “Testicular epidermoid cyst: Sonographic and histologic correlation,” AJR Am J Roentgenol, vol. 174, no. 5, pp. 1547–1549, 2000.
[2] M. S. Dogra, R. J. Gottlieb, and R. Oka, “Sonography of the scrotum,” Radiology, vol. 227, no. 1, pp. 18–36, 2003.
[3] J. D. Lewis and J. M. Babcock, “Testis-sparing surgery for benign testicular masses,” J Urol, vol. 182, no. 4, pp. 2270–2274, 2009.
[4] K. Sakamoto, Y. Iwasaki, and T. Iwasaki, “Magnetic resonance imaging findings of testicular epidermoid cysts,” Urology, vol. 76, no. 5, pp. 1125–1127, 2010.
[5] A. M. Woodward et al., “Imaging of benign and malignant intratesticular lesions,” Radiographics, vol. 22, no. 6, pp. 1467–1484, 2002.
[6] A. Z. Turek, “Benign testicular tumors: Diagnosis and management,” Urol Clin North Am, vol. 41, no. 1, pp. 53–64, 2014.
[7] N. Shah and S. Desai, “Epidermoid cyst of the testis: A case report,” Indian J Pathol Microbiol, vol. 53, no. 3, pp. 562–563, 2010.

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