Clinical History
We present a case of a 17 year old asymptomatic female with an incidental finding seen on a chest radiograph.
Imaging Findings
The abnormality was further investigated by an IV-contract enhanced CT scan of the chest. The selected image shows a large well-defined fat-attenuated mass lesion at the left cardiophrenic angle. The lesion has an internal whorl-like appearing soft tissue component. The lesion drapes around the left cardiac border with no obvious associated mass effect.
Discussion
This case illustrates the classical appearance of an anterior mediastinal thymoplipoma. This is considered a rare aunt minnie in the radiology literature.
Thymolipomas are rare benign thymic lesions, accounting for 2-9% of thymic neoplasms. These lesions have a well formed capsule and are pliable. Since they are slow growing tumours, they are usually large in size when seen. In addition, they sag inferiorly along the anterior mediastinum. They also usually insinuate in between adjacent lung, mediastinum and diaphragm. Histologically, these lesions are mainly composed of mature adipose tissue with intermixed elements of normal thymic tissue and intervening fibrous septations.
This lesion occurs equally in both sexes. Although thymolipomas are typically seen in young adults, an age range of 3-60 years has been documented. Most patients are asymptomatic, with lesions discovered incidentally on radiography or computed tomography (CT). Some patients present with pain, cough, dyspnoea and arrhythmias secondary to mass effect. Fewer cases present with a clinical picture of myasthenia gravis, Graves disease or haematological disorders.
On chest radiography, the lesion usually appears as a sizable mediastinal abnormality. Since the lesion drapes over adjacent structures, it can be confused with cardiomegaly, pericardiac masses, atelactasis, pleural effusion or pulmonary sequestration. One hint to the fatty nature of this neoplasm is that the central dense region enhances with contrast with the periphery enhancing less. However, this is not an easy prospective observation. Smaller lesions might occupy the anterior mediastinum.
The CT appearance usually correlates well with the known gross histological composition of this lesion. The well-defined border reflects the encapsulation of this tumour. A clear-cut fat-attenuated portion is easily observed, representing the mature adipose component. Internal linear soft-tissue whorls are also usually seen, corresponding to the normal thymic tissue and the fibrous septations. No invasive features are seen. The differential considerations for fat-containing lesions on CT would include: teratomas, lipomas, liposarcomas, fat pads, Mediastinal lipomatosis and diaphragmatic hernias.
No treatment is needed for asymptomatic patients, since no malignant potential has been described with such lesions. In symptomatic cases, surgical resection is curative. Some cases show adherent portions to adjacent mediastinal structures, adding technical difficulty to the surgical procedure. No recurrence has been ever documented.
Differential Diagnosis List