Testicular embryonal carcinoma, primarily affecting young adults, is characterised by its complex papillary architecture and typically manifests within a mixed germ cell tumour. Radiologically, it displays a heterogeneous, often hypervascular, intra-testicular mass on ultrasound and CT.
Description
Embryonal carcinoma is a malignant germ cell tumour of the testes that predominantly targets young adults. Part of the non-seminomatous germ cell tumours (NSGCTs), embryonal carcinoma arises from pluripotent primordial germ cells or gonocytes, contributing to its unique embryonic-type tissue composition. While it can present as a pure form, it’s often encountered within a mixed germ cell tumour alongside other NSGCT elements such as yolk sac tumour or teratoma.
Pathogenesis
Embryonal carcinoma’s exact pathogenesis remains somewhat enigmatic. However, it’s widely accepted that these tumours originate from the aberrant differentiation of primordial germ cells or gonocytes. Instead of following the typical maturation route, these cells instead veer towards the formation of embryonic-type tissue, leading to the development of embryonal carcinoma.
Subtypes
No specific subtypes of embryonal carcinoma are recognised, yet it’s common to encounter this entity within a mixed germ cell tumour, adding to the complexity of its clinical presentation and radiological appearance.
Epidemiology, Risk Factors & Associations
- Embryonal carcinoma most commonly targets young adults aged 20-30 years.
- Cryptorchidism, involving unilateral or bilateral undescended testes, forms a significant risk factor.
- There’s an established association with Klinefelter’s syndrome.
Clinical Features
Clinically, patients usually present with a palpable scrotal mass, which can be either painful or painless. A notable clinical sign is gynaecomastia, a condition linked to the tumour’s potential secretion of human chorionic gonadotropin (hCG).
Complications
Embryonal carcinoma, by nature, is an aggressive tumour with considerable metastatic potential. The most frequent metastatic destinations are the retroperitoneal lymph nodes, followed by the lungs, liver, and in some cases, the brain.
Pathological Features
Histopathology
- Macroscopic: The tumour typically exhibits a variegated appearance with ill-defined, lobulated masses. Areas of haemorrhage and necrosis are common.
- Microscopic: The hallmark of embryonal carcinoma under the microscope is its complex papillary architecture, featuring large, pleomorphic cells with prominent nucleoli.
Serology:
- Embryonal carcinoma can raise the serum levels of alpha-fetoprotein (AFP) and hCG.
Biochemistry:
- No unique biochemical features have been reported.
Radiological Features
General Features
- Usually present as heterogeneous hypervascular intra-testicular masses.
CT
- Non-contrast: Displays an inhomogeneous testicular mass, occasionally punctuated by calcifications.
- C+ Arterial: The hypervascular nature of the tumour lends to avid enhancement patterns.
- C+ Venous: Sustained enhancement is seen, with possible necrotic areas due to the tumour’s aggressive nature.
MRI
- T1: Embryonal carcinoma is usually isointense relative to the muscle.
- T2: The tumour shows hyperintensity compared to normal testicular tissue.
- DWI/ADC: Restricted diffusion reflects the tumour’s high cellularity.
- T1 Gad+: Enhancing due to hypervascularity.
US
- B-mode: A heterogeneous, often hyperechoic intra-testicular mass is depicted.
- Colour Doppler: Increased blood flow correlates with the tumour’s hypervascular nature.
NM
- PET FDG: Increased FDG uptake can be detected due to the high metabolic activity of the tumour.
Grading and Staging
The TNM staging system, standard for testicular tumours, applies to embryonal carcinoma. It considers factors such as the extent of the primary tumour, lymph node involvement, and the presence of distant metastases.
Diagnosis
The definitive diagnosis of embryonal carcinoma relies on the histopathological examination of the surgical specimen. Serology provides ancillary support, often revealing elevated AFP and hCG levels in the patient’s blood.
Differential Diagnosis
- Germ cell tumours of the testes: Seminoma typically presents as a homogeneous mass, in contrast to the heterogeneous appearance of embryonal carcinoma. Teratomas might exhibit areas of calcification and fat. Yolk sac tumour and choriocarcinoma share similar presentations but are distinguished by their unique microscopic features.
- Secondary testicular lymphoma: More common in older adults, lymphoma presents as a homogeneous testicular enlargement, differing from the complex appearance of embryonal carcinoma.
Management
The mainstay of treatment is orchiectomy, usually followed by chemotherapy. This approach depends on the tumour’s stage, and the presence or absence of metastasis.