A visual compendium of teratomas and their diverse anatomical locations

Abstract

Teratomas are a common type of germ cell tumours which may be benign or malignant. Benign mature teratomas are the most frequent subtype and typically show intralesional fat and calcifications within a cystic mass. Immature/malignant teratomas are usually larger with irregular solid components, coarse calcifications, small amounts of fat, and with or without necrosis or haemorrhage. Teratomas can manifest in various anatomical locations, particularly in the sacrococcygeal, gonadal, mediastinal, retroperitoneal, and intracranial regions. This article explores the imaging characteristics and diverse locations of teratomas as well as discusses about possible differential diagnoses to facilitate early detection and ensure prompt treatment.

Introduction

Teratomas are the most common germ cell tumour (GCT) typically derived from mature or immature tissues of germ cell origin. The mature teratoma is the most frequently encountered and characteristically contains mature tissues from the ectodermal, mesodermal, and endodermal germ cell layers. ¹ On imaging, the presence of intralesional fat within a cystic mass, often accompanied by calcifications, is pathognomonic for a mature teratoma.

Immature teratomas, akin to their mature counterparts, are comprised of tissues originating from the three germ layers but their histological distinction lies in the presence of immature tissue elements. In addition, there is a subset of teratomas that contain germ cell or non-germ cell neoplastic tissue. This subset, together with immature teratomas that show evidence of metastasis, is grouped as malignant teratomas. Compared to mature teratomas, immature/malignant teratomas are usually larger in size on initial presentation, with a large irregular solid component containing coarse calcifications and small amounts of fat, with or without areas of necrosis and haemorrhage. ²

Teratomas can manifest in nearly any anatomical location but exhibit a predilection for sacrococcygeal, gonadal, mediastinal, retroperitoneal, and intracranial sites. ³ This article explores the imaging characteristics and diverse locations of teratomas as well as discusses about possible differential diagnoses to facilitate early detection and ensure prompt treatment.

Intracranial teratoma

Intracranial teratomas are rare brain tumours and represent a very small percentage (0.3%–0.6%) of all intracranial neoplasms. They commonly occur in the pineal or suprasellar regions. ⁴ Clinical presentation may include Parinaud’s syndrome due to mass effect on the superior tectal plate, visual disturbances secondary to optic chiasm compression, or signs of obstructive hydrocephalus. Serum alpha fetoprotein (AFP) and b-human chorionic gonadotropin (b-HCG) are known to be elevated in patients with malignant teratomas. ⁵

On computed tomography (CT), intracranial teratoma is frequently seen as a solitary mass with cystic areas, fat components, and patchy/punctate calcifications.^4,6 On magnetic resonance imaging (MRI), they appear as fat-containing ovoid or irregular masses which are heterogeneous in both T1-weighted (T1W) and T2-weighted (T2W) sequences. They usually also show heterogeneous enhancement and may be multiloculated in appearance (Figure 1).^4,7 The heterogeneous appearance on MRI corresponds to the myriad components within the lesion, such as fibrosis, fat, calcification, cystic elements, hair follicles, cellular debris, and keratinocytes. For malignant teratomas, contrast-enhanced MR images may show marked heterogeneous enhancement, possibly due to angiogenesis in their solid components. ⁴

Figure 1.

Intracranial immature teratoma in a 17-year-old male. Axial T1W (A) and axial T2W (B) MR images show a multiloculated pineal mass containing a fat-fluid level (arrows). Axial post-contrast T1W (C) MR image shows heterogeneous enhancement within the mass (arrowhead). Sagittal T1W (D) MR image shows the irregular and elongated morphology of the pineal mass which extends into the third ventricle, thalami, and midbrain (triangular arrows).

Possible differential diagnoses for intracranial teratoma would include dermoid cyst or lipoma which is also fatty in appearance but the former frequently presents as a unilocular cystic mass in the parasellar region or anterior cranial fossa, while the latter would typically be of homogeneous fat attenuation/signal intensity.

Mediastinal teratoma

The anterior mediastinum is the most common extragonadal location for teratomas. Mediastinal GCTs represent 15% of all mediastinal tumours in adults and a higher proportion of 24% in the paediatric population. ⁸ Benign teratomas are frequently asymptomatic and often detected incidentally during chest radiographs performed for other reasons. When symptoms do occur, they typically result from mass effect, leading to cough, dyspnoea, or chest pain. Trichoptysis is rare but a pathognomonic symptom. ⁸

Imaging of mediastinal mature teratomas often depict them as heterogeneous, well-defined, spherical, and lobulated anterior mediastinal masses that can contain soft tissue, fluid, fat, or calcifications (Figures 2 and 3). ⁹ While similar in appearance to mature teratomas, mediastinal immature teratomas are primarily distinguished by prominent areas of enhancing soft tissue or by presenting as irregular, thick-walled cystic masses containing areas of haemorrhage and necrosis. ¹⁰ These tumours may also cause the effacement of tissue planes or direct invasion of mediastinal structures.

Figure 2.

Anterior mediastinal mature teratoma in a 30-year-old female. Frontal chest X-ray shows a large mediastinal mass projected over the right perihilar region. The presence of the hilum overlay sign indicates that the hilum is visualized despite the superimposed mass, which implies that the mass does not originate from the hilum itself. The normal appearance of the vertebrae lends additional support to an anterior mediastinal location.

Figure 3.

Anterior mediastinal mature teratoma in a 30-year-old female. Contrast-enhanced axial (A) and coronal (B) chest CT images show a heterogeneous anterior mediastinal mass containing macroscopic fat and fluid with no calcifications. There is mass effect and compressive atelectasis of the adjacent right lung upper lobe.

Thymolipoma is a possible differential to consider but typically presents as an almost entirely fatty mass with bands of soft tissue, resulting in a ‘whorled’ appearance. ¹¹ Lymphoma or other malignant GCTs with cystic change may mimic mature teratomas that lack internal fat attenuation but are typically associated with lymphadenopathy, large soft tissue components, or evidence of invasion which are not features of mature teratomas.

Retroperitoneal teratoma

Primary retroperitoneal teratomas are most frequently diagnosed in neonates and young adults and account for 1%–11% of retroperitoneal neoplasms. ¹² Within the paediatric population, retroperitoneal teratomas constitute the third most frequently encountered retroperitoneal tumours, after neuroblastoma and Wilms tumour, and comprises 2%–5% of all teratomas diagnosed in children.^13,14

Retroperitoneal teratomas are often asymptomatic and might be discovered by chance. However, as these tumours grow, they can cause obstructive symptoms like abdominal pain and distension, gastrointestinal issues (nausea, vomiting, constipation), and subcutaneous oedema in the lower extremities from lymphatic blockage. In their study involving 142 infants and children, Billmire et al. observed elevated AFP levels in all cases of malignant teratomas and in 6% of mature teratomas. ¹⁵

CT or MRI is the modality of choice for evaluation of retroperitoneal teratomas. The presence of a heterogeneous, well-defined mass containing fluid, fatty regions, and calcifications is highly indicative of a teratoma (Figure 4). Features suggestive of malignant teratomas include a predominantly solid morphology, thickened walls, irregular borders, and invasion of adjacent organs.^16,17

Figure 4.

Retroperitoneal mature teratoma in a 53-year-old lady. Contrast-enhanced axial (A) and coronal (B) abdominal CT images show a mixed-density mass in the right aspect of the retroperitoneum (triangular arrows) with mass effect on the surrounding bowel loops, pancreatic head, and right kidney. The mass contains fat, fluid, and calcifications.

Retroperitoneal well-differentiated liposarcomas may potentially be mistaken for a teratoma and appear as fatty masses with thickened nodular septations that show enhancement. Well-differentiated liposarcomas that undergo dedifferentiation may even show calcifications in up to 30% of cases. ¹⁸ Large adrenal myelolipoma or renal angiomyolipoma are also potential mimics but while they show macroscopic fat, they typically do not contain fluid or calcifications.

Ovarian teratoma

The ovarian mature cystic teratoma (MCT), also known as a dermoid cyst, accounts for over 95% of all teratomas, 69% of all germ cell tumours, and a significant portion of ovarian tumours in both adults (20%) and children (50%).^19,20 Often discovered incidentally during imaging for other reasons, MCTs are typically asymptomatic. However, when symptoms are present, they may involve abdominal pain, distension, or complications from ovarian torsion, haemorrhage, or rupture of the cystic lesion.

On ultrasound, MCTs can appear as cystic, solid, or complex masses, often containing echogenic sebaceous material and calcifications. Three common sonographic findings are: cystic lesion with an echogenic tubercle (known as Rokitansky nodule), diffusely or partially echogenic mass with sound beam attenuation caused by sebaceous material and hair, and multiple thin echogenic bands caused by hair strands. ²¹

CT is highly effective for diagnosing MCTs, showing characteristic features like fat-fluid levels, a ‘floating ball’ (made of sebum, keratin, and hair), and Rokitansky nodules. ²¹ In contrast, immature ovarian teratomas may demonstrate large irregular solid components, coarse calcifications and small foci of fat (Figure 5). ²² While pelvic liposarcoma or large uterine lipoleiomyoma are within the list of differential diagnoses, precise identification of the gonadal vessel’s relationship to the mass may aid in determining its ovarian derivation.

Figure 5.

Synchronous left ovarian mature cystic teratoma and right ovarian immature teratoma in a 30-year-old female. Contrast-enhanced axial (A) and coronal (B) abdominopelvic CT images show a smoothly marginated, predominantly fatty mass in the left ovary (arrows) with calcifications and Rokitansky nodules. Contrast-enhanced axial (C) and coronal (D) abdominopelvic CT images show a large solid-cystic mass arising from the right ovary with scattered calcifications and small amounts of fat.

Representing about 3% of ovarian teratomas, struma ovarii is a monodermal variant primarily composed of thyroid tissue. Clinical manifestations of hyperthyroidism are observed in approximately 5% of affected individuals, with a similar percentage developing papillary thyroid carcinoma. On cross-sectional imaging, it typically presents as a lobulated, hypervascular solid-cystic mass. Non-contrast CT is helpful for accurate diagnosis as iodine follicles within the tumour appear as areas of high attenuation.^23–25

Testicular teratoma

Testicular teratomas represent 50% of mixed GCTs and 3%–7% of non-seminomatous germ cell tumours. ²⁶ GCTs are classified into types I, II, and III based on their developmental origin, histological characteristics, and molecular features. ²⁷ The differentiation between type I (prepubertal) GCTs and type II (postpubertal) GCTs is clinically important as prepubertal GCTs typically exhibit a benign course and are associated with a favourable prognosis. ²⁸

Postpubertal teratomas are more common than their prepubertal counterparts and are predominantly observed in young adults. ²⁹ Somatic-type malignancies develop in 3%–6% of testicular GCTs and are exclusively seen in postpubertal teratomas. Sarcomas are the most frequently observed histological type, with over half being rhabdomyosarcomas. ³⁰ The most frequent clinical presentation for testicular teratoma is a painless testicular lump but pain may arise if there is haemorrhage, rupture, or torsion. ²³

On ultrasound imaging, both prepubertal and postpubertal teratomas are heterogeneous lesions that can be solid, cystic, or both (Figure 6). Postpubertal teratomas have been described as cystic in appearance in 28.5%, solid in 21.5% and mixed in 50% of cases. Calcifications and fibrosis within these tumours may produce echogenic foci and varying levels of shadowing. These structures typically show poor to mild vascularization on colour Doppler.^21,23,31 Findings on CT or MRI may align with observations made on ultrasound (Figure 7) and are generally reserved for evaluating distant metastasis or assessing complex cases.^21,32

Figure 6.

Postpubertal mixed GCT (mature teratoma and seminoma) of the left testis in 31-year-old male. Ultrasound transverse (A) and longitudinal (B) images of the left testis show a mixed solid-cystic intratesticular lesion which demonstrates internal vascularity on colour Doppler (C).

Figure 7.

Postpubertal mixed GCT (mature teratoma and seminoma) of the left testis in 31-year-old male. Contrast-enhanced axial (A) and coronal (B) pelvic CT images demonstrate a heterogeneous solid-cystic lesion in the left testis which fairly correlates with the sonographic findings.

Primary testicular lymphoma is a potential differential for testicular GCTs, though it’s more common in older men, particularly those over 60. ³³ Although lymphoma is also usually associated with unilateral testicular involvement, past studies have indicated bilateral testicular involvement and lymphoma tends to easily infiltrate the epididymis as well as other nearby structures like lymph nodes. ³⁴ Other differentials to consider would be testicular metastasis especially if the patient has a known history of malignancy and testicular epidermoid cyst, though this typically shows a lamellated ‘onion skin’ appearance and is non-vascular in nature.

Sacrococcygeal teratoma

The sacrococcygeal region is the most common location for teratomas in the paediatric population, making up 40%–70% of cases. ³⁵ Sacrococcygeal teratomas (SCTs) are the most common GCTs in neonates, with an incidence of about 1 in 27,000 live births and a female-to-male ratio of 3:1 to 4:1.^36–38 Although most SCTs are benign at birth, malignant transformation is possible. ³⁶ Malignant transformation can occur as children age, with roughly 70% of SCTs becoming malignant by 9 months of age. ³⁹

Detection of SCTs is typically done on prenatal ultrasound examinations. Large tumours carry the risk of dystocia or other delivery complications. Following birth, the tumour presents as a subcutaneous mass in the caudal region. Significant tumour size may lead to ulceration and necrosis of the overlying skin. While some individuals are asymptomatic, others may experience obstructive symptoms of the intestines or bladder.^39,40

Based on their morphology, the American Academy of Paediatrics Surgery Section Survey proposed a classification system that categorizes SCTs into four types: type I SCTs are primarily external, with only a minor presacral portion; type II SCTs are externally visible but also possess a notable intrapelvic component; type III SCTs have a small visible external part, accompanied by a significant pelvic mass that extends into the abdominal cavity; type IV SCTs are entirely confined to the presacral area, with no external manifestation. ⁴¹ Type I SCTs are the most common, followed in prevalence by types II, III, and IV. ⁴²

SCTs show diverse imaging characteristics, often appearing as heterogeneous masses with varying amounts of cystic and solid components. The contents of the cystic components can also differ, containing various degrees of fat, haemorrhage, and calcification (Figure 8). While imaging alone cannot predict the exact histologic subtype, benign SCTs typically have more cystic components, calcification, and prominent fatty tissue compared to malignant ones. Conversely, the presence of large solid components, haemorrhage, and/or necrosis within the mass is more indicative of malignant SCTs.^39,43

Figure 8.

Type I sacrococcygeal matured teratoma in a 20-day old neonate. Axial T1W (A), axial T2W (B), sagittal T1W (C), and sagittal T2W (D) MRI of the lumbosacral spine show a subcutaneous solid-cystic mass in the sacrococcygeal region (arrows) with small foci of T1W and T2W hyperintensity (C and D, triangular arrow), in keeping with fat content.

While sacral chordoma is a possible differential diagnosis, its presentation is more typical in adults, whereas SCTs are predominantly encountered in the paediatric demographic. Unlike chordomas which characteristically cause bony destruction, SCTs do not typically result in such destruction unless they are malignant. ⁴⁴ An additional differentiating factor is the absence of fatty components in chordomas. Sacral meningoceles and tailgut duplication cysts are also in the list of differentials but are generally purely cystic lesions and do not contain fat, solid, or calcific elements characteristic of teratomas.

Conclusion

Teratomas manifest in a diverse array of anatomical locations and exhibit a broad spectrum of imaging appearances as a direct consequence of their varied cellular origins. Consequently, radiologists should possess a full appreciation of these variations. While diagnostic imaging plays a crucial role in identifying teratomas and differentiating them from other tumours, a definitive diagnosis always requires histopathological confirmation.