Cystic Lymphangioma - not always a pediatric neoplasm

Clinical History

A 52-year-old man presented with mild dyspnoea and non-productive cough, not associated with fever. He had no previous medical history.

Imaging Findings

Chest radiograph shows a sharply delineated mass located at the right of the trachea, presenting silhouette sign with the superior vena cava and the proximal aortic arch (Fig. 1). The hilum overlay sign is also present, as we see the right pulmonary hilum superimposed on the mass. It occupies the superior mediastinum in its entirety (Fig. 2).
Unenhanced CT shows a hypodense lesion of fluid attenuation (0-20 UH), extending vertically from the thoracic outlet to the carina region and edged laterally by the lungs (Fig. 3-5). It has lobulated but sharp limits. It surrounds the mediastinal vascular structures and the trachea without invading or compressing these structures. Contrast-enhanced CT does not show any enhancement of the lesion's wall. No other abnormalities are seen (Fig. 6).
MRI shows a heterogeneous intermediate intensity sign on T1WI (Fig. 7). T2WI shows a homogeneous high signal intensity with thin septa (Fig. 8-9).

Discussion

The patient underwent bronchofiberoscopy, obtaining biologic material for cytologic analysis. The results showed large amounts of lymph-like material, without signs of malignant disease, confirming the diagnosis of lymphangioma.
Lymphangiomas are benign congenital malformations of the lymphatic tissue, frequently occurring in children but extremely rare in adults [1, 2]. They usually appear in the head, neck, axilla and mediastinum although they can affect any part of the body [1, 3]. They can be classified histologically as simple, cavernous or cystic (also known as hygroma), the latter being the commonest, depending on the size of the lymphatic channels they contain. They have no malignant potential [4].
Clinically, they rarely produce symptoms although there have been reported cases presenting with cough, dyspnoea, dysphagia or superior vena cava syndrome. [1, 5] The radiographic findings are nonspecific. However, a mediastinal mass was suspected on the first radiograph and thus a CT was performed.
There are two distinctive characteristics seen on CT that point towards the correct diagnosis and narrow the differential diagnosis: 1) It is a cystic-like mass (0-20 UH); 2) It envelops the mediastinal structures without invading or compressing them.
On contrast-enhanced CT there is little to no contrast uptake by the lesion, ruling out the possibility of a mediastinal haemangioma [1].
On MRI, T1WI can show either low, intermediate or high signal intensity, depending on the amount of proteinaceous material in the cystic cavity [1, 3, 4]. T2WI almost invariably shows high-signal-intensity in a homogenous way, typical of cystic masses; sometimes, some thin septa are seen, although they are not required for the diagnosis [1, 4].
A differential diagnosis of mediastinal cystic masses should include congenital cysts like bronchogenic or enteric duplication cysts, thymic and pericardial cysts, mediastinal abscess, haemangioma, teratoma or even pancreatic pseudocyst [1, 4]. In this particular case, the two distinctive characteristics seen on the CT rule out congenital, thymic and pericardial cysts (they usually compress adjacent structures) and teratoma (as it is usually heterogeneous). There is no evidence in the patient’s history to support the abscess or pseudocyst alternative.
Complete excision is the mainstay of therapy, although the patient refused it [1, 4, 5]. He remains asymptomatic to the present date.
In conclusion, if a cystic mass is found that envelops adjacent structures without compressing or invading them, especially if located in the neck or mediastinum, cystic lymphangioma should always be considered in the differential diagnosis, even in an adult.

Differential Diagnosis List

Final Diagnosis

Cystic lymphangioma of the mediastinum

URL:	https://www.eurorad.org/case/11574
DOI:	10.1594/EURORAD/CASE.11574
ISSN:	1563-4086