Testicular Epidermoid Cyst: Imaging Diagnosis, Differential Diagnosis, and Evidence-Based Management

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 Introduction

Testicular epidermoid cyst is a rare, benign intratesticular lesion that accounts for approximately 1–2% of all testicular tumors. Despite its benign nature, it represents a critical diagnostic challenge because its imaging appearance may overlap with malignant germ cell tumors. An accurate diagnosis is essential to avoid unnecessary radical orchiectomy, particularly in young men of reproductive age.

With the evolution of high-resolution scrotal ultrasound and multiparametric MRI, testicular epidermoid cyst has become one of the few testicular lesions that can be confidently diagnosed preoperatively. This column provides a comprehensive, evidence-based review of testicular epidermoid cyst, focusing on pathophysiology, epidemiology, clinical presentation, imaging features, differential diagnosis, diagnosis, treatment, and prognosis, based on the most authoritative and recent global literature.

Pathophysiology

A testicular epidermoid cyst is a benign epithelial-lined cyst containing keratin debris. Histologically, it is composed of:

  • A fibrous capsule
  • Lining of stratified squamous epithelium
  • Keratinized debris within the lumen
  • Absence of skin appendages (distinguishing it from dermoid cyst)

The origin remains controversial. The most widely accepted theories include:

  1. Monodermal variant of teratoma (currently less favored)
  2. Congenital inclusion of ectodermal tissue
  3. Post-traumatic or inflammatory epithelial inclusion

Crucially, no malignant germ cell components are present, which explains the excellent prognosis.

Epidemiology

  • Incidence: ~1–2% of testicular tumors
  • Age: Most commonly diagnosed in second to fourth decades
  • Laterality: Slight right-sided predominance
  • Tumor markers: AFP, β-hCG, LDH are normal
  • Pediatric cases: Rare but documented

Given its rarity, testicular epidermoid cyst is frequently misdiagnosed as malignant testicular cancer.

Clinical Presentation

Most patients present with:

  • Painless, palpable testicular mass
  • Slowly enlarging lesion
  • Occasionally discovered incidentally during scrotal ultrasound

Notably:

  • No systemic symptoms
  • No hormonal abnormalities
  • No metastatic signs

Pain or tenderness is uncommon and suggests alternative diagnoses such as torsion or infection.

Imaging Features

Figure Display Notice


Figure 1. Scrotal Ultrasound – “Onion Skin” Appearance; High-resolution scrotal ultrasound demonstrates a well-defined, intratesticular, avascular mass with characteristic concentric hyperechoic and hypoechoic rings, known as the “onion skin” or “target” sign, highly suggestive of a testicular epidermoid cyst.

Key imaging features:

  • Well-circumscribed lesion
  • Hypoechoic or mixed echogenicity
  • Lamellated internal echoes
  • No internal vascularity on color Doppler

Figure 2. MRI T2-weighted Imaging; T2-weighted MRI shows a sharply demarcated intratesticular lesion with concentric alternating signal intensity rings, corresponding to layered keratin content.

Key MRI findings:

  • T1: Variable signal intensity
  • T2: Onion-ring appearance
  • DWI: Restricted diffusion due to keratin
  • Post-contrast: No enhancement 

Figure 3. Contrast-Enhanced MRI; Contrast-enhanced MRI confirms absence of internal enhancement, effectively excluding malignant germ cell tumors.

Differential Diagnosis

Differential diagnosis of testicular epidermoid cyst includes:

  1. Seminoma
    • Homogeneous hypoechoic mass
    • Increased vascularity
    • Elevated tumor markers (occasionally)
  2. Non-seminomatous germ cell tumor
    • Heterogeneous echotexture
    • Necrosis or hemorrhage
    • Elevated AFP or β-hCG
  3. Testicular abscess
    • Clinical signs of infection
    • Peripheral hyperemia
  4. Burned-out tumor
    • Fibrotic scar
    • Microlithiasis
  5. Intratesticular hematoma
    • Trauma history
    • Evolution over time

The onion-skin appearance with avascularity is highly specific for testicular epidermoid cyst.

Diagnosis

The diagnosis is based on a combination of:

  • Typical imaging findings
  • Normal serum tumor markers
  • Lack of vascularity
  • Clinical stability

Definitive diagnosis may be achieved via:

  • Testis-sparing surgery with frozen section
  • Histopathologic confirmation

Treatment

Standard Management Options

  1. Testis-sparing surgery (preferred)
    • Indicated when imaging features are classic
    • Preserves fertility and endocrine function
  2. Radical orchiectomy
    • Reserved for indeterminate imaging
    • Still commonly performed due to diagnostic uncertainty

Current guidelines increasingly favor organ-preserving approaches.

Prognosis

  • Excellent prognosis
  • No malignant transformation reported
  • No recurrence after complete excision
  • No metastatic potential

Long-term follow-up is generally not required once diagnosis is confirmed.

Quiz

Question 1

A 28-year-old man presents with a painless testicular mass. Ultrasound shows a well-defined avascular lesion with concentric echogenic rings. Tumor markers are normal. What is the most likely diagnosis?

A. Seminoma
B. Testicular abscess
C. Testicular epidermoid cyst
D. Leydig cell tumor

Answer & Explanation

Answer: C

Explanation:
The onion-skin appearance with absent vascularity and normal tumor markers is classic for testicular epidermoid cyst.

Question 2

Which imaging feature most reliably differentiates testicular epidermoid cyst from malignant tumors?

A. Size
B. Patient age
C. Lack of enhancement on MRI
D. Testicular pain

Answer & Explanation

Answer: C

Explanation:
Absence of enhancement confirms lack of vascularity, excluding malignancy.

Question 3

What is the preferred management when classic imaging features of testicular epidermoid cyst are present?

A. Chemotherapy
B. Radiotherapy
C. Radical orchiectomy
D. Testis-sparing surgery

Answer & Explanation

Answer: D

Explanation:
Testis-sparing surgery preserves fertility and is appropriate for benign lesions.

References

  1. Dogra VS et al., “Sonographic features of testicular epidermoid cysts,” Radiology, vol. 210, no. 1, pp. 159–164, 1999.
  2. Woodward PJ et al., “From the archives of the AFIP: tumors and tumorlike lesions of the testis,” Radiographics, vol. 22, pp. 189–216, 2002.
  3. Cassidy FH et al., “MR imaging of scrotal tumors,” Radiographics, vol. 30, pp. 665–683, 2010.
  4. Tsili AC et al., “MRI of the scrotum,” AJR, vol. 204, pp. 552–563, 2015.
  5. Langer JE et al., “Imaging of testicular tumors,” Ultrasound Quarterly, vol. 35, pp. 223–234, 2019.
  6. Laguna MP et al., “Testis-sparing surgery,” European Urology, vol. 68, pp. 1045–1052, 2015.
  7. WHO Classification of Tumours of the Urinary System and Male Genital Organs, 5th ed., IARC, 2022.

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