Diffuse form of fibrosing mediastinitis causing stenosis of multiple mediastinal vessels

Clinical History

A 50-year-old male patient presented with a 4-month history of dyspnoea on exertion associated with occasional fever, wheezing and cough with minimal expectoration. On examination breath sounds were decreased on right side with stony dull note. A few prominent veins were seen in the neck.

Imaging Findings

Chest radiograph showed right pleural effusion with widening of the mediastinum (Fig. 1). CT chest showed an ill-defined minimally enhancing soft tissue with calcifications (Fig. 2), encasing multiple mediastinal vascular structures. The soft tissue was encasing and severely narrowing the calibre of superior vena cava with enlarged azygous vein (Fig. 3), and a few collaterals in the upper chest and neck. All the branches of the aortic arch were encased with mild narrowing of left common carotid and left subclavian arteries (Fig. 4). Main and right pulmonary artery were encased with associated narrowing (Fig. 5). Extending inferiorly there was extrinsic compression of left atrium with narrowing of bilateral inferior pulmonary veins (Fig. 5). Right main bronchus was encased by the lesion, but there was no stenosis. There was moderate right pleural effusion. Under CT guidance, multiple biopsy samples were obtained from the mediastinal lesion, which showed dense hyalinised fibrous tissue. There was no evidence of malignancy.

Discussion

Fibrosing mediastinitis is a rare benign disorder characterized by slowly progressive proliferation of dense fibrous tissue within the mediastinum, enveloping mediastinal structures [1]. It is also known by synonyms like sclerosing mediastinitis, mediastinal fibrosis, chronic mediastinal fibrosis or cryptogenic mediastinal fibrosis [2].
The disease often presents in young patients with clinical symptoms due to compression of mediastinal structures or in about 40% of cases incidentally [1, 3].
It presents in two forms- focal granulomatous form and diffuse nongranulomatous form [5]. Focal granulomatous form is considered to be due to proliferation of fibrous tissue secondary to granulomatous infections such as histoplasmosis, tuberculosis, aspergillosis, blastomycosis, mucormycosis and cryptococcosis [5]. The aetiological factors for diffuse nongranulomatous form are autoimmune conditions, treatment with methysergide, radiotherapy, retroperitoneal fibrosis, Behçet's disease and primary sclerosing cholangitis [5].
Histopathology shows aggregates of lymphocytes and plasma cells within a hyalinised fibrous connective tissue [3].
Chest radiographs may show non-specific widening of the mediastinum [1].
Computed tomography (CT) is the best modality for evaluation of these patients. On CT also, two distinct forms of mediastinal involvement are described. The more common, localized mediastinal disease predominantly affecting the right paratracheal and subcarinal regions, associated with stippled calcification and the less common, diffusely infiltrating type, affecting multiple mediastinal compartments [1]. Patients with localized form typically have evidence of prior granulomatous infection, while the latter have not, but have other associated conditions like retroperitoneal fibrosis [1].
There is frequent involvement of the mediastinal vascular and tracheobronchial structures by the lesion, with more than 90% of patients showing obstructive/ compressive changes in the major vessels or airways [6]. Superior vena cava obstruction is the most common manifestation [3]. Obstruction of the pulmonary veins, presenting as parenchymal abnormalities such as ground glass opacities and involvement of pulmonary arteries and veins can result in infarcts [1]. CT can demonstrate the level and extent of stenosis of these vessels.
CT is also useful in determining severity and extent of airway or oesophageal narrowing if they are involved [1].
On T2 W MRI images fibrosing mediastinitis characteristically shows areas of low signal intensity due to fibrous tissue and calcification [1].
There is no proven effective medical therapy for fibrosing mediastinitis. Corticosteroids and tamoxifen have been tried [4]. Palliative treatment such as grafts for SVC obstruction, dilatation of bronchial and oesophageal strictures can be of some help [2]. In cases of localized disease, surgical resection of affected tissues may be curative [1].
It is important to recognize this rare entity and differentiate it from other infiltrative disorders of mediastinum like lymphoma and metastatic carcinoma.

Differential Diagnosis List

Final Diagnosis

Fibrosing mediastinitis

URL:	https://www.eurorad.org/case/11710
DOI:	10.1594/EURORAD/CASE.11710
ISSN:	1563-4086