Description
Testicular teratomas, classified as non-seminomatous germ cell tumours (NSGCTs), represent diverse tumours with cells from one or more of the three germ layers (ectoderm, mesoderm, and endoderm). These tumours can present at any age but have distinctive clinical features depending on the age group, often being malignant in post-pubescent males. The tumours exhibit varied behaviour across age groups, with typically benign manifestations in infants and malignant tendencies in post-pubescent males.
Pathogenesis
Testicular teratomas, like other germ cell tumours, are thought to arise from gonocytes or primordial germ cells. These cells undergo abnormal differentiation, producing multiple different cell lines. This results in the varied histological appearances of teratomas, which can contain tissues derived from any of the three germ layers: ectoderm, mesoderm, or endoderm.
Epidemiology, Risk Factors & Associations
- Comprise approximately 5% of all testicular tumours in adults.
- The prevalence is higher in paediatric testicular tumours, where they account for 40-50% of cases (most common paediatric testicular tumour is yolk sac tumour).
- The peak incidence occurs in Caucasian males aged between 15-40 years.
- Key risk factors:
- Cryptorchidism or undescended testes (this condition is associated with approximately a 3-5 fold increased risk), regardless if previously surgically corrected.
- A personal or familial history of testicular cancer (about 1.5-3 fold increased risk)
- Certain genetic conditions such as Klinefelter syndrome (the risk in this population is roughly 50 times higher than in males without the syndrome)
Clinical Features
- Most patients (70-80%) present with a painless testicular mass.
- A smaller proportion may experience testicular discomfort or pain (10-20%).
- In cases of metastatic disease, symptoms may include back pain and respiratory symptoms.
Complications
- Complications are primarily related to metastatic disease.
- The most common sites of metastasis include the retroperitoneal lymph nodes (65-70%), lungs (20-25%), liver, and brain.
Pathological Features
On gross pathology, testicular teratomas often appear as heterogeneous masses with variable cystic and solid areas.
Histopathology
Microscopically, testicular teratomas are characterised by the presence of multiple types of tissue from one or more of the three germ layers. This can include structures resembling organ systems, such as skin (ectoderm), muscle or fat tissue (mesoderm), or gut-like structures (endoderm). The degree of differentiation can range from well-differentiated to immature tissues, which are more aggressive and more likely to metastasise.
Radiological Features
Scrotal US
- The first-line imaging technique for testicular masses.
- Teratomas appear as heterogeneous, often hyperechoic masses with calcifications in around 60% of cases.
CT
- Mainly utilised for cancer staging and evaluation of metastasis.
- Teratomas exhibit variable appearances due to the diverse tissue types, ranging from fat density to dense calcifications.
MRI
- Complementary to CT for staging and metastasis evaluation.
- Provides more detailed information about the composition and extent of the tumour.
Grading and Staging
Grading of testicular teratomas is primarily based on the degree of tissue differentiation, with immature teratomas being more aggressive. Staging follows the TNM system, taking into account the extent of the primary tumour, lymph node involvement, and the presence of distant metastasis.
Differential Diagnosis
- Mixed Germ Cell Tumours (MGCTs): These tumours contain two or more types of germ cell tumour. They are common and account for approximately 40-60% of all germ cell tumours. On ultrasound, they often appear as heterogeneous masses. Serum tumour markers such as AFP or beta-hCG may be elevated. MGCTs are more aggressive than pure seminomas, with a higher propensity for metastasis.
- Seminoma: Typically occurs in men aged between 25-45 years and accounts for 35-50% of all testicular tumours. Clinically, they present as a painless testicular mass. On ultrasound, seminomas usually appear as homogeneous hypoechoic lesions within the testis. Unlike teratomas, seminomas are radiosensitive and respond well to radiotherapy.
- Embryonal carcinoma: This is a rare form of testicular cancer, accounting for 2-3% of all cases. It usually affects younger men (20s to early 30s). Embryonal carcinomas are more likely to spread to other parts of the body than teratomas. On ultrasound, they may have a heterogeneous appearance with areas of necrosis or haemorrhage.
- Yolk sac tumour: Most common form of testicular cancer in children, less common in adults. It often presents as a painless scrotal mass in a young boy. Serum alpha-fetoprotein (AFP) levels are often elevated. On imaging, yolk sac tumours may appear as mixed echogenic masses.
- Leydig cell tumour: These tumours are usually benign and often cause symptoms related to the production of testosterone (e.g., early puberty in boys). On ultrasound, they typically appear as hypoechoic lesions.
- Sertoli cell tumour: These tumours are rare and typically benign. They may produce oestrogen, leading to symptoms of feminisation. On ultrasound, Sertoli cell tumours typically appear as well-defined, homogeneous, hypoechoic masses.
- Testicular lymphoma: This is the most common testicular tumour in men over 60. It often presents with a rapidly enlarging testis. On ultrasound, testicular lymphoma usually appears as a hypoechoic mass with homogeneous texture.
Management
- Management typically involves orchiectomy to remove the affected testis.
- Depending on the stage and type of the tumour, further treatment may include chemotherapy, radiotherapy, or retroperitoneal lymph node dissection.
- Surveillance is an important part of managing testicular teratomas due to the risk of recurrence or metastasis.
- Regular follow-up with serum tumour markers and imaging is recommended.