Teaching Case

An 84-year-old woman was admitted to the emergency department with complaints of medical treatment-refractory upper back pain with irradiation to right hypochondrium and epigastrium. No respiratory symptoms. The blood test revealed a slight increase in cholestasis enzymes, acute phase reactants, and lymphopenia.

Initial chest X-Ray (fig. 1) showed increased density and widening of the lower posterior mediastinum due to lateral displacement of both right and left paraspinal lines.

Contrast-enhanced CT (fig. 2) demonstrated a homogeneous infiltrative soft-tissue mass along the right and left paravertebral areas, with smooth and regular margins towards the lung parenchyma, elevating and encasing the descending thoracic aorta in 360 °. Patent intercostal arteries traversed the mass and at the dorsal levels D3-D6, it extends into the spinal canal through the widened conjunction foramina. There was no evidence of pleural effusion or adenopathies within the mediastinum. 

Transthoracic biopsy of the mass (fig. 3) was performed under CT guidance, and samples of tissue were obtained and sent to the Department of Anatomic Pathology to be histologically analyzed (fig. 4).

Follow-up 18 F-FDG PET/CT (fig. 5) was performed after medical treatment, showing complete disappearance of the mass and absence of radiopharmaceutical uptake.

Chest lymphoma involvement can occur in various anatomical locations such as mediastinal nodes,  the lung, oesophagus, chest wall or breast [1,2]. Within the mediastinum, it commonly emerges as multiple lymphadenopathies. Lymphoma is also well known as one of the most common causes of a mass in the anterior mediastinum, either with extranodal origin in the thymus or nodal affecting lymphatic ganglia [1-3].

Rarely is the posterior mediastinum the site of lymphoma. In any location imaging tests are an essential tool to suggest the diagnosis and guide the interventional procedures for its histological analysis [3,6,7]. Conventional radiology was a key point in our patient, demonstrating displacement of both right and left paraspinal lines, which helped to suggest its subsequently posterior mediastinal location.

In CT, these tumours manifest as a homogeneous and infiltrative mass. However, areas of necrosis appear within the mass if remarkable size is reached, giving it a heterogeneous appearance. Moreover, CT is useful to assess local extension and distant nodal involvement, relevant for its correct staging [4,5].

Several findings supported the suspicion of lymphoma: firstly, the encasement of the thoracic descending aorta without transmural invasion, known as the “floating aorta sign“ [1]; secondly, the presence of patent intercostal arteries traversing the mass at their origin, known as “vessel penetrating sign“; thirdly, its extension into the spinal canal through the widened conjunction foramina; finally,  the absence of destruction of vertebrae cortices. Other findings that may be present are pleural effusion or nodular thickening in the adjacent pleura and vertebral pathological fractures [1,4]. 

MR is a useful imaging technique when secondary spinal cord or nerve compression is suspected and in some cases of bone marrow or muscle involvement.  On the other hand, PET-CT imaging is more sensitive in diagnosing nodal involvement and it is helpful in monitoring and assessing response to chemotherapy [1,3].

Final diagnosis was achieved after transthoracic biopsy. Results confirmed diffuse large B-cell lymphoma, which is characterized by the presence of lymphoid cells with nuclear size equal or exceeding normal macrophage nuclei or more than twice the size of a normal lymphocyte with a diffuse growth pattern, effacing the architecture and infiltrating the adipose tissue. Signet ring cells and occasional mitosis are seen. A combination of chemotherapy and the monoclonal antibody rituximab, with or without radiation therapy, can lead to disease remission in a large number of patients with this form of lymphoma. . However, the prognosis is fatal if left untreated [8].

Written informed patient consent for publication has been obtained.