Anterior mediastinal mass

Clinical History

A 68-year-old man with severe chronic obstructive lung disease (COLD) was hospitalized with dyspnoea. He had a history of two acute myocardial infarctions and a coronary artery bypass grafting (CABG) performed in 1988. A chest x-ray showed a round radiopaque structure in the anterior mediastinum and a CT was recommended.

Imaging Findings

The chest x-ray showed an anterior mass, best seen on the lateral view (fig 1). Afterwards a contrast enhanced CT of the thorax was performed (fig 2-4). A homogeneous, rounded structure was seen in the anterior-superior mediastinum in close relation to the heart and large vessels. In the periphery some calcification was present. A vessel containing contrast was seen within the structure. The average Hounsfield value of the structure was 32.
At first, the suspicion of a thymoma was raised due to the location in the anterior mediastinum. The patient was referred to a CT-guided biopsy of the suspected thymoma. Before any biopsies were taken, a senior radiologist reviewed the CT and ruled out a thymoma and correctly diagnosed a large aneurysm on the graft from the patients bypass surgery.

Discussion

The mediastinum is often divided into an anterior, middle and posterior part. Fifty percent of mediastinal tumours are placed in the anterior part [1, 2]. Typical masses in the anterior mediastinum are thymoma, teratoma, seminoma, lymphoma, carcinoma, parathyroid adenoma, intrathoracic goiter, lipoma, lymphangioma and aortic aneurysm [2].

With an incidence of 0, 15% cases per 100000 people thymomas are the most frequent primary tumor [1, 2]. The size of thymomas are typically 5-10cm but as large as 34cm have been reported and they are often found in the superior-anterior mediastinum on either side of the midline. Radiologically, thymomas are rounded or lobulated, they are well defined and can contain calcification, hemorrhage, necrosis and/or cysts. They can invade surrounding structures [1, 2]. Thymomas are divided into high- and low-risk depending on histology and invasiveness and classified according to the Masaoka staging system [3, 4].

A saphenous vein graft (SVG) aneurysm after CABG is considered to be rare, with an incidence of less than 0, 1% [5, 6]. Most patients develop SVG-aneurysm more than 10 years after surgery (68, 5%). SVG-aneurysms of up to 10 cm have been reported and are often found as mediastinal or hilar masses. The diagnosis of a thymoma is often made on a CT-scan. It is important to evaluate complications such as fistulation, compression of nearby structures, rupture and the status of native coronaries. A supplementary coronary CT angiography can be helpful [5, 6].

The patient of this case had dyspnoea because of COPD, but shortness of breath is a primary symptom of both SVG-aneurysm and mediastinal masses [1, 5]. The patient died from his COPD a year after the CT. The family did not want an autopsy. However an SVG aneurysm had been diagnosed by coronary angiography in 2008.

Quite a few points can be learned from this case. It shows the importance of a relevant clinical history, knowing the possible differential diagnoses and most important the need to look into earlier diagnostic procedures. In this case several doctors, including the radiologist, missed the fact that the diagnosis of a SVG aneurism had been made several years earlier. Even though the diagnosis had not been made earlier, the information about earlier surgery in the area in question could have helped the radiologists minimize the number of differentials. This case also shows the large consequences a radiologist’s diagnosis can have for further investigation and treatment. It could have been fatal if a biopsy had been taken.

Differential Diagnosis List

Final Diagnosis

Saphenous vein graft aneurysm after CABG

URL:	https://www.eurorad.org/case/12918
DOI:	10.1594/EURORAD/CASE.12918
ISSN:	1563-4086