- Benign, painless.
- Laminated keratin debris without teratoma components. Onion skin ultrasound appearance.
Description
A testicular epidermoid cyst is a rare, benign, non-germ cell tumour of the testis, characterised by the presence of keratin-filled cysts lined by squamous epithelium. Unlike teratomas, epidermoid cysts lack other germ cell components. These cysts are most often found in young adult males and are typically discovered incidentally or due to the presence of a painless mass. They account for about 1-2% of all testicular tumours. The term “epidermoid” refers to the resemblance to epidermal structures, specifically the keratinising squamous epithelium.
Pathogenesis
The exact origin of testicular epidermoid cysts is uncertain. They are believed to arise from squamous metaplasia of surface mesothelium or from trapped surface ectodermal cells during embryogenesis. These cysts are composed entirely of squamous epithelium and keratin without involvement of other germ cell layers, distinguishing them from mature teratomas.
Subtypes
Testicular epidermoid cysts do not have distinct subtypes but can be categorised based on their appearance and histological features. All share the common characteristic of being lined by keratinising squamous epithelium.
Epidemiology, Risk Factors & Associations
- Approximately 1-2% of testicular tumours.
- Most common in young adult males, typically in their second to fourth decades of life.
- No specific risk factors identified.
- No known associations with other conditions or syndromes.
Clinical Features
- Painless testicular mass.
- Occasionally associated with discomfort or mild pain if the cyst becomes large.
- Generally, no systemic symptoms.
- Incidental finding during physical examination or imaging for unrelated reasons.
Complications
- Considered benign with no malignant potential.
- Complications from Surgery: Potential for damage to the testicular tissue or infertility if bilateral involvement and extensive surgery are required.
Pathological Features
Histopathology
- Macroscopic: Well-circumscribed, firm nodule within the testis, often with a pearly white appearance on cut section.
- Microscopic: Cyst lined by stratified squamous epithelium, filled with laminated keratinous material. No evidence of other germ cell layers or malignant cells.
Serology
- Normal tumour markers (AFP, beta-hCG, LDH).
Biochemistry
- Generally normal; no specific biochemical abnormalities.
Radiological Features
General Features
- Firstline Investigation: Scrotal ultrasound.
- Gold Standard Imaging Protocol: High-resolution ultrasound with Doppler.
- Typical onion skin appearance with concentric, alternating hypoechoic and hyperechoic rings.
Ultrasound
- B-mode:
- Well-defined, round or oval lamellated lesion with or without a central cystic components.
- Characteristic onion skin or target appearance due to concentric layers of keratin.
- May show an anechoic rim representing the cyst wall.
- Colour Doppler: Typically avascular or showing minimal peripheral vascularity, which helps distinguish it from malignant tumours.
Grading and Staging
There is no specific grading or staging system for testicular epidermoid cysts due to their benign nature. Diagnosis is based on clinical and imaging findings, confirmed by histopathology.
Diagnosis
- Clinical examination and patient history.
- Ultrasound showing characteristic features.
- Confirmation via histopathological examination after surgical excision or biopsy.
Differential Diagnosis
- Testicular Cancer: Typically presents with a solid mass with increased vascularity on Doppler ultrasound; elevated tumour markers (AFP, beta-hCG).
- Testicular Teratoma: May show heterogeneous echogenicity with cystic and solid components, including calcifications, often associated with elevated tumour markers.
- Hydrocele: Fluid collection around the testicle, appearing anechoic on ultrasound without internal layers.
- Spermatocele: Cystic dilatation of the epididymal duct, usually separate from the testis and appearing anechoic on ultrasound.
- Infectious or Inflammatory Lesions: May show increased blood flow and lack the characteristic “onion skin” appearance.
- Intratesticular abscess: Intratesticular abscesses are often the sequelae of an epididymo-orchitis and are symptomatic. These are more commonly seen in immunocompromised patients.
Management
- Referral to urology for evaluation and management.
- Standard treatment involves enucleation of the cyst while preserving as much normal testicular tissue as possible.
- Postoperative follow-up to monitor for recurrence or complications, though recurrence is rare.