Giant Thymolipoma

Clinical History

Thymolipoma is a rare benign thymic mass of the anterior mediastinum typically containing mature fat and strands of connective and thymic tissue. They are occasionally very large at presentation and may have characteristic CT appearances.

Imaging Findings

A 44 year old patient presented with a history of mild chest discomfort. Initial frontal chest radiograph (Fig.1) demonstrated a large mass obscuring the right hemidiaphragm and right heart border imitating combined right middle and lower lobe collapse. A CT (Fig.2,3) revealed a mediastinal mass of predominantly fat attenuation containing a few strands of higher attenuation soft tissue. After surgical excision via an extended thoracotomy and sternotomy, histological examination revealed a mass of mature adipose tissue containing elements of atrophic thymic tissue with no features of atypia or malignancy.

Discussion

Thymolipomas are rare benign mediastinal tumours. They are encapsulated tumours composed mainly of mature adipose tissue with thin swirling strands of residual thymic tissue [1,2,3]. Very rarely, thymolipomas have been found to contain foci of thymoma and thymic carcinoma at histological diagnosis [4]. Thymolipomas have an equal frequency in men and women [3]. They mainly occur in the lower anterior mediastinum, often filling the cardiophrenic angles [1]. Thymolipomas may be an incidental finding or present with chest pain and sometimes respiratory failure if they achieve a massive size [5]. Most are diagnosed in early adulthood but can become very large before detection and because of their size and position, thymolipomas may mimic cardiomegaly, lobar collapse, pleural effusion or a raised hemidiaphragm particularly on projectional chest radiographs [1,6]. On CT, thymolipomas are well-demarcated masses of fat attenuation containing higher attenuation strands of connective tissue septa draped over the mediastinal surface. The CT differential diagnosis includes mediastinal lipomatosis, liposarcoma and an eccentric overgrowth of a cardiophrenic fat pad. On MRI, thymolipomas have fat and soft tissue signal characteristics. Typically the adipose tissue within the tumours returns a high T1 signal and the thymic tissue component a more intermediate T1 signal [1,2]. Thymolipomas are associated with a range of different conditions including myasthenia gravis, aplastic anaemia, Grave’s disease and hypo-gammaglobulinaemia [2].

Differential Diagnosis List

Final Diagnosis

Giant Thymolipoma

URL:	https://www.eurorad.org/case/8167
DOI:	10.1594/EURORAD/CASE.8167
ISSN:	1563-4086