CHEST RADIOLOGY


Case 8:

A 40-year-old female presents with breathlessness of one-month duration. Following a plain radiograph of chest, a CT scan was performed. 
What is the diagnosis?

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Imaging Findings

 

Study reveals a mediastinal mass lesion with peripheral calcification and intense enhancement, and local mediastinal invasion.

Histology following CT guided FNAC

 

Thymoma

Discussion
Thymomas affect men and women with equal frequency, generally afflicting adults above 40 years of age. Approximately 50% of thymomas are discovered incidentally on radiographs in asymptomatic individuals taken for other reasons. 25-30% of persons present with symptoms from compression of adjacent mediastinal structures including the trachea, recurrent laryngeal nerve, and esophagus. Sudden cardiac death due to right artrial compression may occur. Thymomas may be associated with myasthenia gravis, and other systemic disorders including pure red-cell aplasia, hypogammaglobinaemia, endocrine, and connective tissue disorders. These parathymic syndromes occur in 40% of patients with thymomas and invasive thymomas occur in 30-40% patients.

Imaging Findings
Radiographs of chest reveal a contour abnormality of the anterior mediastinum, as the mass displaces both visceral and parietal pleura, resulting in smoothly marginated lobulated borders against the lung. They may extend to both sides of the mediastinum or may arise in the cardiophrenic angle. Calcification is common, is usually linear, thin and peripheral.

CT
Replacement of the anterior mediastinal fat by denser soft tissue is the primary sign. Thymomas appear as solid, oval or rounded homogenous soft tissue masses, predominantly on one side of the midline, usually bosselated/ lobulated, and in close relation to the root of the aorta and pulmonary artery. Mediastinal involvement by thymomas is usually intrathoracic and mostly pleural.

MRI
Multiplanar imaging is useful for thymoma evaluation. Thymomas are usually iso intense on T1WI, with increased signal intensity on T2WI. Malignant lesions have an inhomogenous signal, which may be related to cystic/ hemorrhage within.

Staging
Masaoka Classification includes 5 stages, staging is usually performed at the time of surgical intervention.

  1. No capsular invasion
  2. capsular/pleural invasion
  3. Invasion of surrounding tissue (lung, pericardium, SVC)

4a. Dissemination in the thoracic cavity (pleural & pericardial seedling)

4b Lymphogenous and / or hematogenous spread

Stage 1 is non-invasive and stages 2-4b are invasive

Therapy
Surgical resection is the preferred treatment for patients. Total thymectomy is recommended, and us associated with complete remission in 80-95% cases.  Use of radiotherapy is controversial, and is advocated as an adjunct to surgical excision for cases of invasive thymoma, especially when only subtotal excision has been performed. In recurrent/ metastatic tumor, chemotherapy may play a limited role if at all (CAP regime of cyclophophamide, cisplatinum & adriamycin).

Contribution
Dr. Sanjeev Mani, Mumbai

References
Yang WT, Metreweli C. Plain radiography & computed tomography of invasive thymomas: Clinico-radiologic-pathologic correlation. Australas Radiol 1997, 41: 118-124.

Crowe JK, Brown LR, Nuhm JR. Computed Tomography of the Mediastinum. Radiology 1978; 128: 75-87