An anterior mediastinal mass

A 64-year-old woman was sent to the hospital for evaluation of a suspected mass in her left breast. A preoperative chest radiograph showed en enlarged mediastinum. On chest CT, an anterior mediastinal mass was found. To further characterise and stage this mass, a PET-CT was performed.

A preoperative chest radiograph showed an enlarged mediastinum, suggestive of a mediastinal mass (Fig. 1). A PET-CT was performed to characterize and stage this mediastinal mass.
Contrast-enhanced CT scan showed an encapsulated mass in the anterior/middle mediastinum. It contained soft tissue and fat densities (Fig. 2), but also multifocal and irregular calcifications in the mass were seen (Fig. 3). The presence of fat and calcifications made the diagnosis of teratoma highly suggestive. A compression of the pulmonary trunk and the left hilum was present (Fig. 4). No lymphadenopathy or metastases were detected.
FDG-PET (Fig. 5) and PET-CT (Fig. 6) showed a voluminous mass with a hypermetabolic rim but no central FDG uptake. There were no FDG-avid distant lesions.
This mediastinal mass was surgically removed. The mass showed a mixture of hair, sebum, bone, synovium and cartilage (Fig. 7). The diagnosis of a mediastinal teratoma was made.

Benign mature teratomas are tumours that belong to the group of germ cell tumours, typically occur in young patients and have an approximately equal sex ratio. They are derived from primitive cells that fail to migrate completely during early embryonic development. They predominantly consist of ectodermal elements including skin, sebaceous gland, hair and calcification.
Mediastinal teratomas account for 10-20% of all mediastinal tumours and are usually found in the anterior mediastinum [1]. Most patients are completely asymptomatic as the tumour grows slowly. As they enlarge they may cause symptoms by compressing surrounding structures. Extrinsic compression of the heart and great vessels appears to be very rare [2, 3]. Benign teratomas do have the potential to undergo malignant transformation into a variety of malignancies as rhabdomyosarcoma, adenocarcinoma, leukaemia and anaplastic small cell tumours [4].
Diagnostic assessment of mediastinal tumours is performed with plain chest radiographs and chest CT. Although the presence of fat and calcification within an anterior mediastinal mass suggests a teratoma, the preoperative diagnosis is often difficult on plain films because of the inability to detect the fat or calcification. CT accurately estimates the density of all included tissues, such as soft tissue (in virtually all cases), fluid (88%), fat (76%), calcification (53%) and teeth, which are considered specific imaging findings [5, 2]. MRI is a very valuable tool in detecting the anatomical relations to the mediastinal and the hilar structures, like vessels and airways. A large anterior mediastinal mass with a well-defined wall and predominantly cystic component is highly suggestive of a benign cystic teratoma. With calcifications in the wall of the mass or small spherical or irregular calcifications within the mass, mature cystic teratoma is even more likely. Unequivocal fat within the mass, particularly a fat-fluid level, makes this diagnosis certain.
Complete surgical resection is the treatment of choice, but also subtotal resection can relieve symptoms.