Case No. :	18
Month :	June
Year :	2000
Contributor :	Dr. Titty Thomas

Case Report | Radiological Findings | Differential Diagnosis & Discussion

Case Report :

A 35-year-old man came with complaints of an anterior chest wall swelling which was troubling him since four months. This swelling was gradually increasing in size. There was no pain fever, weight loss or any other local or systemic complaint.

Clinical examination revealed a firm, 3 x 2 cm swelling contiguous with the sternum at the angle of Lewis. A diagnosis of a chest wall tumor was made and chest radiographs obtained.

Fig.1
Fig.2	Fig.3

 

Radiological Findings :

The frontal radiograph of the chest (Fig 1) revealed a large soft tissue mass in the inferior part of the anterior mediastinum with well defined borders with the medial border merging with the heart. There was no evidence of calcification within the lesion.

The lateral radiograph revealed a bulge of the manubrium sternum at the junction with the body of the sternum. This bulge was caused by a retrosternal soft tissue swelling merging with the heart.

A plain and contrast enhanced CT scan of the thorax was obtained (Figs 2, 3) to evaluate the lesion . Plain scans revealed a large hypo to isodense soft tissue mass

10 x 8 cm in the anterior mediastinum. There were areas of curvilinear calcification in the periphery of the lesion. There were no calcifications within the lesion, nor was there evidence of caseation. The margins were well defined and well circumscribed except anteriorly where it caused erosions of the junction of manubrium and body of the sternum. Contrast enhanced scans revealed a well-circumscribed area of intense enhancement within the lesion. This was surrounded by an area of non-enhancement. The soft tissue anteriorly causing destruction of sternum was seen to extend anteriorly into the chest wall like an outpouching from the main swelling. This swelling was seen contiguous with the ascending aorta with extension into the root at its origin from the left ventricle

Differential Diagnosis and Discussion :

The clinical diagnosis of a bone tumour arising from the sternum could not be justified by the findings on frontal and lateral radiographs. There were no areas of bone mineralisation within the soft tissue mass. Chondrosarcoma may not show mineralisation of the matrix in one third .But the well defined ,sharply marginated lesion with a thin zone of transition ruled it out .Mediastinal lymph node mass was a possibility. The absence of lobulation of the lateral border and total absence of any lesion in left hilar and left paratracheal region in the presence of such a large lesion on the right made a lymph node mass a less likely possibility.

Germ cell tumours can occur anterior mediastinum. The medial border which is not seen separately from the heart ruled out the possibility. Teratomas which are basically of germ cell origin usually show areas of calcification within them.

Thymomas are the commonest tumours in this region .They present as slow growing soft tissue masses in the superior and anterior mediastinum in the 4^th and 5^th decades.

They are usually spherical or oval in shape and may show lobulated borders. Calcification punctate and curvilinear may be seen in both the benign and malignant forms of thymoma. Radiographically this lesion was indistinguishable from a thymoma But the well circumscribed area of intense enhancement within the centre of the lesion pointed to a vascular lesion. The peripheral curvilinear calcification pointed to the calcification of a vessel wall which is enormously dilated .The area of intense enhancement within the lesion represented the blood in the lumen of the vessel. The hypodense area surrounding the hyperdense area suggested thrombosis within the vessel.

A diagnosis of aneurysm of ascending aorta was made.

The two most important causes of true aortic aneurysms are atherosclerosis and cystic medial degeneration. Syphilis also causes aortic aneurysms.

Atherosclerosis, the most frequent etiology for aneurysms causes arterial wall thinning through medial destruction secondary to plaque that originates in the intima. Atherosclerotic aneurysms usually occur in the abdominal aorta, most frequently between the renal arteries and iliac bifurcation, but the arch and descending aorta can be commonly involved.