Resident Cases

Home > Resident Case Studies > Week 2 Case 4 > Case 4 Discussion

RESIDENT CASE STUDIES

Week 2 April 28 - May 2, 2003: Case 4

A 87 year old female with an anterior mediastinal mass (substernal)

Discussion--Invasive thymoma:
This is a malignant epithelial neoplasm of thymus and anterior mediastinum. There are different histological variants: epithelial, spindle cell, lymphocytic and mixed. Grossly, these lesions can be multiloculated or solid to cystic. Based on one study, 29-72% of thymomas are invasive. Histologically, these lesions are characterized by: clusters of benign epithelial cells separated by thick fibrous septa, perivascular spaces filled with proteinaceous material and hematopoietic elements, and epithelial pseudorosettes around the perivascular spaces. Spindle cell variant is composed of sheets or fascicles of epithelial cells with elongated nuclei with diffuse chromatin. There is an obvious invasion into the medistinal adipose tissue in this case. This is not a thymic carcinoma as there is no cytologic atypia. These lesions should be followed carefully as they have propensity to recur and metastasize. The patients are usually treated with radiotherapy in addition to the surgery.

Thymoma staging:
Stage I--Intact capsule or growth within the capsule
Stage IIa--Microscopic invasion through capsule into adjacent mediastinal tissue
Stage IIb--Gross and microscopic invasion through capsule into surrounding fat or adjacent pleura or pericardium
Stage III--Invasion into surrounding structures (i.e., great vessels, lung)
Stage IV--Lymphogenous or hematogenous metastasis

Differential diagnoses:

Substernal thyroid: Characterized by thyroid elements with colloid. In this case the history and radiographic findings are suspicious for substernal thyroid, but histologically no thyroid elements are seen.

Thymoma: Benign epithelial neoplasm seen in the anterior mediastinum. Well encapsulated with no evidence of invasion. Very rarely metastasize, majority of the patients are cured by surgical resection.

Thymic carcinoma: Tumor cells are cytologically malignant with invasion into the capsule, adjacent and distant organs. Additional radiation therapy and follow up is required after the surgery. Surgeons should determine the extent of the disease at the time of the surgery.

Teratoma: Usually seen in young patients. Different elements from different germ layers are seen.

Malignant lymphoma: Does not have epithelial component. Patients may have the constitutional symptoms and mediastinal adenopathy. Flow cytometry and other immunohistochemical studies are helpful. Lymphocyte predominant thymomas can mimic lymphomas.

Reference:

Pathology of the Thymus and Mediastinum/Michael J. Kornstein (Volume 33).