Infected tracheal diverticulum mimicking an aggressive mediastinal lesion on FDG PET/CT: an interesting case with review of the literature

Abstract

The differential diagnosis for intense hypermetabolic mediastinal lesions on positron emission tomography (PET) could benefit from the combined morphological and metabolic information present in a fluorodeoxyglucose (FDG) PET/CT study. We report a case of an infected tracheal diverticulum mimicking an FDG-avid malignancy in a patient with a history of chronic lymphoproliferative disease. We review the literature for a systematic approach in the differential diagnosis of cystic mediastinal lesions. The embryological development of the normal tracheobronchial tree is reviewed, followed by a presentation of various congenital and acquired mediastinal lesions. The characteristic CT findings are described for each lesion and the avidity for FDG on PET is mentioned when references are available. This case emphasises that complicated benign processes should be considered in the differential diagnosis of an FDG-avid mediastinal lesion, even in subgroups of patients with significant risk factors for malignancy.

Figure 1

A chest CT performed at presentation showing a large right paratracheal mediastinal lesion displacing the trachea and the oesophagus to the left. Note the relatively hypodense necrotic centre.

Figure 2

Fluorodeoxyglucose positron emission tomography/CT selected images showing intense activity at the periphery of a large mediastinal mass with a relatively hypometabolic centre. The lesion had a maximal standardised uptake value of 9.2. It extended from the sternal notch following the right paratracheal groove inferiorly to the antecarinal area and displaced the trachea and the oesophagus to the left.

Figure 3

A chest CT performed a few months earlier than that in Figure 1, demonstrating the uninfected tracheal diverticulum. Note the air density within the rounded lesion as well as the communication with the trachea, which is typical for a tracheal diverticulum.