Mature mediastinal teratoma is the most common germ cell tumor of the anterior mediastinum, constituting 60-70% of all mediastinal germ cell tumors. It contains mature tissues originating from two or three germ layers (ectoderm, mesoderm, endoderm) — various tissue components such as fat, cartilage, bone, teeth, hair, skin, and respiratory/gastrointestinal epithelium. It occurs in young adults (20-40 years) with equal gender distribution (unlike seminoma). On CT, the combination of fat, calcification (teeth/bone), and soft tissue components is pathognomonic — this three-component appearance is not seen in any other anterior mediastinal mass. Surgical resection is curative; risk of malignant transformation is low (1-2%). Rupture is rare but a serious complication — may open into pleural or pericardial space causing chemical peritonitis/pleurisy. Tumor markers (AFP, beta-hCG) are normal in mature teratoma.
Age Range
15-40
Peak Age
25
Gender
Equal
Prevalence
Uncommon
Mediastinal teratoma originates from totipotent or pluripotent germ cells that remain ectopically in the mediastinum during embryonic development. These cells can differentiate into any of the three germ layers: ectoderm (skin, neural tissue, hair), mesoderm (fat, cartilage, bone, muscle), and endoderm (gastrointestinal and respiratory epithelium). In mature teratoma, all tissues are well-differentiated and mature — no immature elements are present. The pathognomonic three-component appearance on CT directly reflects this multipotent differentiation: fat component from ectodermal/mesodermal adipose differentiation, calcification from mesodermal cartilage/bone/tooth formation, and soft tissue component from various mature tissues. Fat-fluid level formation results from sebaceous secretion (low-density fat) floating above aqueous fluid within the cyst — fat remains on top due to gravity. Rupture complication develops from capsule integrity disruption due to increased intracystic pressure or trauma; contact of cyst contents with serosal surfaces triggers severe chemical inflammation.
Mass containing fat (-40 to -120 HU) + calcification/bone/teeth (>100 HU) + soft tissue (30-50 HU) in the anterior mediastinum = pathognomonic for mature teratoma. This three-component combination is not found together in any other anterior mediastinal mass and is diagnostic.
On non-contrast CT, mediastinal teratoma appears as a well-defined, encapsulated, heterogeneous mass in the anterior mediastinum. Pathognomonic three components: (1) fat-density areas (-40 to -120 HU), (2) calcification foci (teeth, bone fragments, cartilage calcification — >100 HU), (3) soft tissue density solid components (30-50 HU). Fat-fluid level may be seen in large cystic lesions. Cyst wall may be thin or thick; calcified cyst wall is not uncommon. This three-component appearance is unique among anterior mediastinal masses and is diagnostic.
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A well-defined, encapsulated mass measuring approximately ___ × ___ cm in the anterior mediastinum is seen, containing fat-density areas, calcification foci, and soft tissue components — the three-component appearance is consistent with mature teratoma.
In the arterial phase, solid components and septa of teratoma show enhancement; fat and cystic areas do not enhance. Thin or thick capsule may enhance. Enhancement degree of solid components depends on mature tissue type — fibrous tissue shows moderate, vascular tissue shows avid enhancement. If rupture is suspected: peritumoral fat plane loss, fat droplets within pleural/pericardial effusion, and surrounding tissue inflammation should be sought.
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In the arterial phase, solid components of the mass show enhancement while fat and cystic areas do not enhance; the capsule shows ___ enhancement.
On T1-weighted images, the fat component of teratoma shows high signal (bright). Fat-fluid level is clearly distinguished. Other components show variable signal: proteinaceous fluid intermediate-to-high, serous fluid low, solid components intermediate signal. Signal loss of fat component on fat-suppressed sequences confirms fat presence. Hemorrhagic findings (hyperintense areas) may suggest rupture complication.
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On T1-weighted images, high-signal fat component is seen within the mass with a fat-fluid level; this component shows signal loss on fat-suppressed sequences.
On T2-weighted images, teratoma shows heterogeneous signal. Cystic/fluid components are markedly hyperintense (bright), fat component intermediate-to-high hyperintense, solid components show variable (low-to-intermediate) signal. Calcifications are low signal on all sequences (signal void). On STIR sequence, fat component is suppressed and cystic/solid differentiation is made clearer. T2 sequences are useful for evaluating relationship with mediastinal structures (pericardium, great vessels, trachea, esophagus).
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On T2-weighted images, the mass shows heterogeneous signal with hyperintense cystic areas, intermediate hyperintense fat component, and variable-signal solid components.
In large cystic teratomas, a fat-fluid level may be seen within the cyst — sebaceous material (low-density fat, -40 to -100 HU) floats above the aqueous phase. This finding is seen as the anterior portion being at fat density and the posterior portion at fluid density in the supine patient. Fat-fluid level increases the diagnostic reliability of teratoma. Calcified wall or peripheral calcifications may accompany.
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A fat-fluid level is seen within the cystic lesion, with fat density (-__ HU) in the anterior portion and fluid density (___ HU) in the posterior portion.
Teratoma rupture is rare (1-3%) but a serious complication. CT rupture signs: (1) cyst wall discontinuity, (2) peritumoral fat plane loss and soft tissue inflammation, (3) fat-density droplets within pleural or pericardial effusion (pathognomonic), (4) pleural thickening, (5) mediastinal fat tissue inflammation. Rupture creates severe inflammatory response due to chemical irritation of cyst contents. May present with acute chest pain and fever.
Report Sentence
Cyst wall discontinuity and surrounding inflammatory changes are seen in the teratoma, with fat-density droplets within the pleural effusion — findings consistent with rupture.
On ultrasonography (limited by transthoracic approach), teratoma may be seen as a complex cystic-solid mass. Fat component appears echogenic, cystic component anechoic, solid components show variable echogenicity. Calcifications produce prominent posterior acoustic shadowing. Dermoid mesh (hair and sebaceous material) may appear as echogenic punctate echoes. Ultrasonography is limited for mediastinal lesions but may provide accessory diagnostic information.
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On transthoracic US, a complex cystic-solid mass is seen in the anterior mediastinum with echogenic fat component and calcifications producing posterior acoustic shadowing.
Criteria
Predominantly cystic, contains mature tissues. Well-differentiated, no malignancy potential. Most common subtype (80-90%).
Distinct Features
Large cystic component on CT, fat-fluid level, thin wall. High-signal fat on T1 MRI. AFP and beta-hCG normal. Surgical resection curative.
Criteria
Predominantly solid, contains mature tissues (cartilage, bone, muscle, fibrous tissue). Cystic component minimal.
Distinct Features
Heterogeneous solid mass on CT, prominent calcifications, minimal cystic areas. Unlike seminoma, calcification is prominent. Surgical resection curative.
Criteria
Contains immature (embryonal/fetal) tissue elements — usually neuroepithelial component. Grading based on amount of immature tissue (Grade 0-3). Malignancy potential present.
Distinct Features
More heterogeneous than mature teratoma on CT, less prominent fat component, more solid components. AFP may be mildly elevated. Chemotherapy may be needed.
Criteria
Development of somatic-type malignancy within mature teratoma (most commonly sarcoma, carcinoma, PNET). Very rare (1-2%). Poor prognosis.
Distinct Features
Rapid growth on CT, newly developing heterogeneous solid component, invasive margins. Focal intense FDG uptake on PET-CT. Biopsy required.
Distinguishing Feature
Seminoma is homogeneous, lacks fat and calcification; teratoma is heterogeneous, characterized by fat+calcification+soft tissue triad.
Distinguishing Feature
Thymoma homogeneous or lobulated solid mass, lacks fat and calcification; teratoma complex cystic-solid, three-component.
Distinguishing Feature
Thymic cyst simple cystic, no fat or calcification, thin smooth wall; teratoma complex, contains fat+calcification.
Distinguishing Feature
Lymphoma homogeneous or necrotic, no fat content; teratoma distinguished by fat component. B symptoms may accompany lymphoma.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralMature mediastinal teratoma is a benign tumor and surgical resection is curative. The pathognomonic three-component appearance on CT usually allows diagnosis without biopsy. For surgical planning, the relationship of the mass with great vessels, pericardium, and airways should be evaluated. Urgent surgery may be needed in suspected rupture. Biopsy and adjuvant therapy should be planned if immature elements or malignant transformation is suspected.
Mature teratoma is a benign lesion and surgical resection is curative. Rupture or compression symptoms may develop. Risk of malignant transformation is very low and recurrence after surgery is rare.