The most likely diagnosis is: a) Large spontaneous right pneumothorax with complete right lung collapse

Apart from the large lobulated mass in the medial right hemithorax that is evident on the chest x-ray (CXR) (Fig. 1), you should also note the relative increased lucency of the entire right hemithorax in comparison to the left side, and the associated paucity of any lung markings and vessels on the right side. The mass lesion in fact represents the collapsed right lung tissue. In this case, thankfully, the pneumothorax was not under any tension, as there is notably no mediastinal shift towards the left side. If that finding is present, the situation becomes a lot more urgent and insertion of a large bore chest tube into the right hemithorax becomes priority number one. Another finding that may be present in a tension pneumothorax is inversion of the ipsilateral hemidiaphragm from increased intrathoracic pressure (also not present in our case). In the end, this woman was treated with a right chest tube with resultant complete re-expansion of her right lung, with no underlying lung pathology present, and had a complete recovery.

All of the other differential diagnoses are at least potentially possible with the chest x-ray shown, except for the large clue of the right hemithorax lucency in keeping with a massive pneumothorax. That finding would not be present with the other potential diagnoses (except to some degree with the embolus diagnosis [choice c] discussed below).

Sarcoidosis is a multiorgan granulomatous disease that commonly involves the thoracic structures. Five stages have been described for intrathoracic sarcoidosis — based on the CXR appearance. Stage 0 involves a normal CXR; Stage 1 is hilar adenopathy only (mediastinal adenopathy is typically not well documented on CXR); Stage 2 refers to a combination of lymphadenopathy and lung disease; Stage 3 describes lung disease only; and Stage 4 relates to end-stage fibrotic lung disease (with or without hilar adenopathy). Stage 2 and 3 sarcoidosis typically results in fairly symmetric bulky bilateral hilar adenopathy, where the hilar regions reveal a multilobulated configuration rather than the smooth unilateral mass-like appearance in Figure 1. As such, this diagnosis would be highly unlikely.

A large central pulmonary embolus can indeed produce vascular engorgement and hilar vessel enlargement that may be unilateral. The appearance, however, would be more of numerous dilated hilar vessels rather than one mass lesion and as such this diagnosis should not be considered seriously. It should be noted, though, that a large central pulmonary embolus can result in increased lucency to an involved lung segment, or potentially a hemi-thorax, as a result of marked oligemia of the segments affected.

The mass lesion appearance could indeed result from a prominent small cell carcinoma tumour. Typically these primary lung cancers develop centrally and often have associated hilar and mediastinal adenopathy associated, which can increase the central density and mass appearance. That diagnosis could be considered if the diffuse hemithorax lucency was not identified. A thorax CT scan would instantly provide the correct diagnosis.

Since the upper half of the collapsed right lung mass does align with the ascending segment of the thoracic aorta, the thought of an ascending thoracic aortic aneurysm could be entertained. These can be associated with ascending aortic dissection (typically linked with hypertension, which this lady did not have), but can also be isolated in disease entities such as Ehlers-Danlos syndrome, Marfan syndrome, Singleton Merton syndrome, Takayasu’s arteritis, syphilitic or mycotic infective aneurysms, or as a pseudoaneurysm following thoracic trauma — an unlikely diagnosis in this case but again if the hemithoracic lucency were not noted, a thorax CT would indeed differentiate between the two.

 

References

1. Francois CJ, et al. AJR 2008;190:902-6.
2. Prabhakar HB, et al. AJR 2008;190:S1-6.
3. Engelke C, et al. AJR 2006;186:1265-71.