Thymoma or Thymic Cyst

 I was reading a medical journal article this evening and here is its introduction:

The normal thymus evolves over the course of a lifetime, with involution and gradual fatty replacement beginning around puberty. The thymus originates from 3 embryonic germ-cell layers and thus has the potential to transform along a number of neoplastic cell lines. On computed tomography (CT), the normal thymus appears as a triangular-shaped structure in the anterior mediastinum (see Figure 1). Variations in the morphology of the normal thymus gland, along with its association with a diverse range of pathologic processes, can make the thymus an imaging enigma and diagnostic challenge for clinicians.

Figure 1: source 

An abnormal appearance of the thymus can be attributable to either diffuse enlargement of the gland or a discrete mass. Benign thymic hyperplasia and lymphoma can both cause diffuse enlargement of the thymus. Many lesions—including thymoma, thymic carcinoma, and thymic carcinoids—as well as benign lesions—such as thymolipomas and cysts—can present with a focal thymic mass. This is often an incidental finding in an asymptomatic patient undergoing imaging for unrelated reasons. Clinical presentation can play a role in the evaluation of patients with thymic masses. One study found that more than 75% of asymptomatic patients with mediastinal masses had benign lesions, whereas almost two-thirds of symptomatic patients with mediastinal masses had malignant lesions. It has been suggested that expectant management can be considered for observation of asymptomatic patients with diffuse thymic enlargement. For symptomatic patients, biopsy or, at times, resection may be appropriate.

At present, CT remains the imaging modality of choice for the evaluation of mediastinal masses. Magnetic resonance imaging and positron emission tomography (PET) are useful adjuncts. While there is overlap in the features of many thymic lesions on imaging, some lesions have a characteristic appearance on CT. Thymolipoma, an uncommon benign thymic neoplasm, typically manifests on CT as a large anterior mediastinal mass containing fat intermingled with areas of soft-tissue attenuation, which may conform to the shape of other mediastinal structures. On CT, idiopathic multilocular thymic cyst, an acquired benign thymic lesion, cannot be reliably distinguished from the cystic components of malignant thymic lesions, including thymomas, Hodgkin lymphoma, and mediastinal germ-cell tumors. The appearances of thymomas on imaging can vary according to their staging and histologic subtype; lobulated contours, calcifications, and heterogeneous attenuation are associated with more-advanced, rather than early stage, thymoma.

Figure 2: source

The increasing use of CT has led to more-frequent identification of incidental lesions in the anterior mediastinum, and with recent advances in minimally invasive surgical techniques, an increasing number of thymic lesions are referred for surgical evaluation. Consequently, some patients may undergo invasive procedures for ultimately benign disease. If the benignity of a thymic lesion could be determined on imaging with a reasonable level of confidence, then the need for invasive procedures may potentially be obviated for a number of cases. The purpose of this study is to identify imaging features that help distinguish benign thymic lesions from early stage malignant thymic neoplasms.

From this study, we learn that "14% of patients with thymic cysts also had hepatic cysts" and:

A thymic cyst is a benign mediastinal disease which has been reported to be the second most common type of primary mediastinal cyst. Thymic cysts are rare, and the majority are believed to be congenital in origin. Approximately 60% of patients with a thymic cyst were asymptomatic, and the most common symptoms were cough, dyspnea, and chest pain, according to the literature (1,4). However, there were no specific symptoms for thymic cysts. 

Given that an ultrasound revealed that I had one or more cysts on my liver back in 2009, then the possibility increases that I might have a thymic cyst rather than a thymoma. It might be self limiting and not cause any severe problems. Up to this point, I've just assumed that what I had was a thymoma but that may not be the case. As the study says, it's often not possible, using CT, to determine the exact nature of an abnormality in the anterior mediastinum. Surgery may be carried out when it is not necessary. 

What struck me, when looking at the diagram in Figure 1 and similar depictions, is that there's not a lot of room in there and this means trouble when neoplasms or cysts develop. Lately I've been feeling quite tired during the day and fatigue is one of the symptoms of thymoma. For the moment, let's wait and see if my condition worsens or not.