“Mosaic” Pattern on Chest CT Scans of CTEPH, PH Patients Offer Unique Insight Into How Disease Affects Lungs

According to an article entitled “Mosaic Pattern of Lung Attenuation on Chest CT in Patients with Pulmonary Hypertension”  published in the journal Disease on September 7, 2015 and authored by Kamonpun Ussavarungsi et al., a mosaic lung attenuation pattern can be observed in the chest CT scans of patients with pulmonary hypertension. The finding could help improve understanding of how PH impacts the lungs.

A mosaic pattern on chest CT scans was detected in 17 percent (34 out of 189) of study participants. The pattern is believed to be nonspecific and can occur for a variety of reasons, including small airway disease, pulmonary vascular disease, and infiltrative lung disease.  The chest CT showing a mosaic pattern of attenuation is one that shows well-defined areas of brightness and darkness in the lung fields as seen on CT scanning.

The greatest prevalence of mosaic attenuation was noted in 50 percent of patients who had type 4 chronic thromboembolic pulmonary hypertension (CTEPH), as opposed to only 16 percent of patients with group 3 pulmonary hypertension. The main pulmonary arterial size, the ratio between the size of the pulmonary artery and the aorta, and the degree of defect seen in non-perfused segments of the lung were highly correlated with having the mosaic pattern on CT.

On the other hand, factors such as gender, age, functional class, body mass index, and pulmonary function studies did not relate to having the mosaic pattern. In patients who had ventilation/perfusion lung scans, the greater the segmental perfusion deficit, the greater the presence of a mosaic pattern. All of those who had ventilation/perfusion scans were in the group 4 pulmonary hypertension class.

Why does the mosaic pattern occur in pulmonary attenuation? It is believed to be due to an increase in the caliber of the pulmonary vessels (where increased attenuation occurs) associated with decreased vessel size in other areas, where there is lower attenuation because of a lack of blood supply.

The results of the study showed that, while the mosaic attenuation pattern was seen on average in 20 percent of participants, the finding is too nonspecific and cannot be used to diagnose or screen for pulmonary hypertension.  There were more findings of mosaic attenuation found in the group 4 pulmonary hypertension patients, but even in this group, the finding could only be seen in half of all people with group 4 disease.

The mosaic attenuation pattern was only seen in 5 percent of those who had pulmonary hypertension from lung disease causes, 12 percent of those with pulmonary hypertension due to heart disease, and 74 percent of patients who had pulmonary hypertension due to vascular diseases such as a pulmonary embolism, lymphangitis metastasis, idiopathic pulmonary hypertension and  pulmonary veno-occlusive vascular disease.

The end result of the study was that the mosaic attenuation pattern was present in some patients with pulmonary hypertension but the number of patients showing the mosaic pattern was not enough to make the determination that the patient has pulmonary hypertension as the disease.