Mediastinal teratoma: advantages of MR imaging versus CT-scan.

Clinical History

A 65-year-old female patient presented to our hospital with a cough lasting for two months, and reported a recent appearance of severe chest pain and dyspnoea. Her history showed a prior diagnosis and treatment for breast cancer.

Imaging Findings

This patient, with a prior history of breast cancer, was admitted to our hospital with recurrent episodes of cough, over the last two months, accompanied in the last week by dyspnoea and posterior chest pain. A chest radiogram in standard projections was performed, the results of which showed a large opacity in the upper part of thorax, probably in the anterosuperior mediastinum. For a better study, we subsequently carried out a thorax CT scan that confirmed the initial radiographic findings, and showed the presence of an an elliptical formation (50mm MD) in the thymic recess, with calcified walls and a fat-like density, with a presumably benign pattern. A MR exam (flash t1-weighted and haste t-2 weighted sequences) of the chest was required for presurgical evaluation and better tissue characterization. It defined the mass as a neoformation with peculiar benign features (not enhanced after contrast, not cystic, moderately dishomogeneous), with diffusely calcified walls and a strong signal in the t2-weighted sequences, highly suggestive of a predominant composition of fat tissue, not of a malignant formation.

Discussion

The word "teratoma" is derived from the Greek word "teras", meaning monsters. Mature teratomas are neoplasms that may be generated from any germinal layers. Consequently, depending on the cells of origin, these tumours have the potential to express as any of the three mature forms of the germ cell lines, namely the ectoderm, mesoderm and the neuroderm. Their presentation occurs most commonly in the gonads, altough extragonadal localizations are not rare and may develop along the body midline, like in the neurocranium, mediastinum, retroperitoneal space, and the sacrococcygeal region. Between extragonadic localizations, mediastinal teratomas are uncommon, occur in all age groups and with no sex predilection, making up about 5%-10% of all mediastinal neoformations, and are thought to be responsible for approximately 1 in 3400 hospital admissions. About 53% of patients have no symptoms at the time of diagnosis, especially in adult subjects, in whom the tumour is found incidentally after blood exams (which show a high CA 19-9 level with no other explanation possible) or on routine chest radiographs. In symptomatic cases, the presentation is usually in the anterosuperior mediastinum, with predominant respiratory symptoms of chest pain, dyspnoea, and cough. Rarely, the presentation may show a major cardio-vascular engagement, involving the heart and the great vessels.Up to 36% of all mediastinal teratomas may present with dramatic, life-threatening symptoms (pneumothorax, pleural or pericardial effusions, superior vena cava syndrome) in case of rupture (into the lungs and bronchial tree, in the pleural space, pericardial space, or great vessels). Regarding the rupture process of mature teratomas, the most acceptable hypothesis attributes the causal role to the presence of digestive enzymes secreted by the pancreatic tissue, salivary gland tissue, or intestinal mucosa within the tumour: a high amylase activity in the pleural effusion or in the tumour contents is often reported. The other hypotheses offered of chemical inflammation, ischaemia, pressure necrosis and infection, prove to be unreliable. However, in case of a rupture, an early diagnosis and treatment improve the survival rate. The only reasonable treatment of mediastinal teratomas is surgical, and should be performed whenever rupture, mass-effect complications (such as atelectasis of lung tissue, adhesion to or compression of adjacent structures), or a malignant transformation, are present or probable; the results and outcome after surgical resection are excellent. The differential diagnosis includes other mediastinal formations such as a thymoma, lymphoma, lipoma, echinococcus cysts, or a fibrous outcome of mediastinitis. CT is the modality of choice for the diagnostic evaluation of these tumours that typically manifest as a heterogeneous anterior mediastinal mass, encapsulated and well-demarcated, containing soft-tissue, fluid-filled cystic areas, fat, or calcium attenuation, or any combination of the four. This pleomorphic appearance is an important clue to distinguish these lesions from other neoplasms which have a mainly solid composition. Calcification is seen in between 20% and 80% of the cases, which could be focal, rim-like, or rarely represented as teeth or bone. Fat is visible on the CT scan in half of these cases, a finding that is highly suggestive of this diagnosis. The fat-fluid level within the mass is particularly diagnostic. MR imaging, owing to its multiplanar capability and high contrast resolution, often provides superior information about the nature (cystic lesions can appear solid on CT, miming other types of lesions), location, and extent (craniocaudal and intraspinal extension) of disease, not forgetting its high degree of sensitiveness in depicting infiltration of the adjacent structures by a fat plane obliteration.The MRI findings of most cases reveale the presence of oval shaped lesions, with a varied intensity pattern (depending on the composition of the tumour). The wall often has solid protuberant fatty parts with a high signal intensity in T1-weighted images and a moderate signal in T2-weighted images. They eventually present areas of cystic degeneration which are hyperintense on T1-weighted images and hypointense on T2-weighted images. Lesions with spiculated borders, thick capsules, heterogeneous contents, fat plane obliteration around the tumour, or direct invasion into the adjacent structures with or without effusion, are to be retained, at the risk of rupture or malignant degeneration.

Differential Diagnosis List

Final Diagnosis

Mature teratoma of the mediastinum.

URL:	https://eurorad.org/case/3378
DOI:	10.1594/EURORAD/CASE.3378
ISSN:	1563-4086