Testicular germ cell tumors (TGCTs) are the most common testicular neoplasms, occuring in young and middle-aged men and they account for 95% of testicular tumors, with the remainder being due to lymphoma and other less common pathologies.
The overall incidence of germ cell tumors is increasing, but the exact reasons for this are uncertain.
They demonstrate diverse oncogenesis, pathologic findings and clinical-biologic behaviors and the updated 2022 World Health Organization (WHO) classification system has substantial diagnostic and treatment implications.
They have since been categorized into postpubertal tumors—including those derived from a “germ cell neoplasia in situ” (GCNIS)—and prepubertal tumors, including those unrelated to GCNIS.
The first category includes pure seminomas and nonseminomatous germ-cell tumors (NSGCTs), which may be pure or mixed tumors.
Mixed tumors show variable proportions of embryonal carcinoma, yolk sac tumors, postpubertal teratomas, and choriocarcinomas.
This category also includes regressed germ-cell tumors (“burned-out” tumor (BOT)).
TGCTs not derived from GCNIS include spermatocytic tumors, prepubertal-type teratomas (e.g., dermoid and epidermoid cysts, and well-differentiated neuroendocrine tumors), prepubertal mixed teratoma and yolk sac tumors, and prepubertal yolk sac tumors.
Seminoma is considered a GCNIS-derived tumor.
Before the 2016 WHO classification, spermatocytic seminoma was considered a subtype of seminoma; however, since it lacks association with GCNIS, it is now considered a separate entity unrelated to seminoma.
Seminomas typically present as a unilateral homogenously hypoechoic lesion with transnodular vascularity.
Cystic areas and calcifications are uncommon.
NSGCTs tend to be ill-defined heterogeneous lesions with areas of necrosis, hemorrhage, cystic change and calcifications.
At MRI, seminomas are homogeneously T1 isointense and T2 hypointense, with well-circumscribed or lobulated margins.
On diffusion-weighted MRI, marked restricted diffusion secondary to increased cellularity and underlying inflammation can be seen; bandlike hyperenhancement of fibrovascular septa is characteristic of GCNIS.
In comparison, NSGCTs are markedly heterogeneous with a hypointense pseudocapsule at T2-weighted MRI.
They may show heterogeneous areas at T1- and T2-weighted MRI that are secondary to the presence of cystic change, hemorrhage, or necrosis.
Although the ultrasound and MRI appearance of typical unique germ cell lesions has been thoroughly described previously, there are several other rare potential presenting situations that we aim to illustrate, such as: - Burned out tumours The spontaneous regression of primary testicular germ-cell tumours is a rare event whose mechanisms have yet to be understood, resulting in its partial or complete replacement by a patch of fibrosis.
Such lesions have been commonly considered burned-out testicular tumours (BOTTs) and are commonly diagnosed in symptomatic metastatic patients.
The typical ultrasound appearance of a BOTT has been described as a hypoechoic, poorly delineated, hypovascular nodular area, with clustered microliths and macrocalcifications frequently encountered in peripheral areas and focal areas of increased stiffness on SWE.
US findings may be insufficient to prompt orchiectomy as BOTTs can be confused with benign lesions, most avascular or hypovascular testes lesions being benign, including segmental testicular infarction, epidermoid cysts and hematomas.
If a BOTT is suspected on ultrasound, then the presence of an area of reduced enhancement with increased ADC values on MRI makes the diagnosis very likely.
These elevated ADC values should not be taken as a sign of benignity, even if testicular cancer usually appears as a restrictive lesion on diffusion-weighted sequences (low ADC values). (Fig. 1, 2, 3 and 4) To the best of our knowledge, our first case is the only report of an increase in testis volume associated with a diffuse BOTT, as burn out lesions are generally encountered in hypotrophic testes. - Extragonadal germ cell tumors Extragonadal germ cell tumors (EGCTs) with no identifiable testis nodule (Fig. 5 and 6) often develop in midline structures and represent 1% to 5% of all germ cell tumors (GCTs).
Morphological type includes mature/immature teratoma, seminoma, yolk sac tumor, embryonal carcinoma, choriocarcinoma and mixed gonadal GCTs.
Their anatomic distribution varies widely and includes the mediastinum, sacrococcygeal region, neck, retroperitoneum and other rare anatomic sites. - Large or diffusely infiltrating lesions Occasionally, germ-cell tumors may occupy the entire pulp (Fig. 7) or interrupt the albuginea (Fig. 8), infiltrating the epididymis or the tunica vaginalis (T2 lesions) or the spermatic cord (T3). - Purely cystic multilocular lesions Although there have been very rare reports of mucinous or serous cystadenoma or hemangiolymphangioma of the testis, multilocular cystic lesions of the testis with no solid components with thick enhancing septa and loculi with variable echogenicity and signal intensity should remain conspicuous for teratoma, as in Fig.9. - Post-pubertal cystic teratomas with echoic contents Mature teratomas should be considered in patients presenting with non-spherical cystic lesions with heterogeneous echoes in the fluid, representing a mixture of mucinous or sebaceous material, with or without hair follicles. (Fig.10) - Partially cystic seminomas While cystic areas are often encountered in NGCTS and atypical in seminomas, up to ten percent of seminomas may present with varying degrees of cystic change (Fig.11), which some investigators attribute to infiltration and obstruction of the rete testis by tumor.
In most reported cases, the diffuse cystic architecture related to the presence of syncytiotrophoblast giant cells that had undergone massive pseudocystic change. - Torsion and hemorrhage, The commonest presentation of a testicular neoplasm is a hard, painless, palpable slow-growing mass.
Acute painful presentations of testicular neoplasms have a varying rate of incidence, between 0.01% and 10%, of all cases, which illustrates the scarcity of such a presentation among the overall incidence of testicular neoplasms in the general male population.
Preoperative multiparametric ultrasound can thoroughly identify and characterize the underlying lesion and guides surgical approach.
In our case, the intraoperative visual assessment of the testis during the emergency detorsion and orchidopexy didn’t identify the mass and the large mixed GCT with 5 components (yolk sac tumor, post-pubertal teratoma, embryonal cell carcinoma, choriocarcinoma and seminoma) was only discovered on the follow up ultrasound (Fig. 12). - Necrotic tumors Entirely or mostly necrotic testicular tumors present a diagnostic imaging and histopathological challenge and should be distinguished from hematoma, segmental infarction and abscesses.
Patients with testicular infarction or hematoma usually present with acute pain rather than a painless palpable mass.
If the diagnosis is uncertain on the basis of the imaging features and clinical presentation, short-term follow-up imaging in 2–4 weeks may be helpful because hematomas usually decrease in size over time, and areas of infarction will become more avascular and more hypoechoic over time.
MRI and CEUS prove very helpful in differentiating tumors from nonenhancing benign entities as these lesions do not enhance, but the surrounding parenchyma may show avid enhancement, whereas necrotic tumors generally retain some solid enhancing areas (Fig. 13 and 14). - Extensive calcifications The presence on ultrasound of a densely calcified solitary testicular mass carries a differential diagnosis of primarily benign pathologies, including spermatic granuloma, large-cell calcifying Sertoli cell tumour, trauma, tuberculosis, filariasis, calcified Leydig cell tumour, but non seminomatous germ-cell tumors, mainly teratomas, may also display such features.
Mature teratoma in children is often benign, but teratoma in adults, regardless of age, should be considered as malignant.
Teratomas consist of elements derived from more than one germ cell layer (endoderm, mesoderm and/or ectoderm).
Teratomas generally appear as well-circumscribed complex masses on ultrasound.
Echogenic foci representing calcification, cartilage, immature bone and fibrosis are commonly seen. (Fig. 15 and 16) - Iso/hyperechoic lesions Choriocarcinomas and embryonal cell carcinomas (Fig. 17) occasionally appear iso or hyperechoic and should be distinguished from benign lesions, such as hematomas, abscesses and atypical Leydig-cell tumors.
Multiparametric ultrasound and MRI are highly contributive, as NGCTS will display intralesional increased vascularity and stiffness, whereas benign lesions appear either avascular (hematomas and abscesses) or present a mainly peripheral circumferential vascularization with moderately increased stiffness (LCTs).
A feeding vessel is identified on CEUS in some Leydig-cell tumors and their enhancement follows a type 3 time-intensity curve, with avid early enhancement and late wash-out on MRI, whereas NGCTS will have significantly lower ADC values and follow a type 2 enhancement curve. - Invasive tumors with extratesticular development mimicking purely extratesticular lesions Occasionally, germ-cell tumors may display extratesticular growth and be mistaken for an extratesticular lesion.
As in our case, MRI is highly useful in individualising the intratesticular suspicious lesion non visible on ultrasound and the thin parenchymal bridge uniting it to the extratesticular component (Fig. 18 and 19). - Bilateral lesions Bilateral germ cell tumors of the testicles are rare, representing only 1 % of all new cases of testicular cancer, around 30 % of these occurring synchronously.
Interestingly, bilateral synchronous testicular lesions share the same histopathological type, most of them being seminomas, as in our case (Fig. 20).