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Radiology Case
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Radiographic findings: The
cardiac silhouette is severely displaced to the right and the right hemidiaphragm
is cranially displaced. There is atelectasis of the right middle lung
lobe (arrows). There is opacification of the right cranial thorax suggesting
focal fluid accumulation or atelectasis of the right cranial lung lobe.
Mild sternal lymphadenopathy is suspected. There is an incidental finding
of mild spondylosis in the thoracic and lumbar spine.
Radiographic impression: The findings suggest atelectasis of the right middle lung lobe and focal fluid accumulation. The sternal lymph node is likely a reactive node; however neoplasia cannot be excluded.
Comments: The word atelectasis is derived from the Greek words ateles (imperfect) and ektasis (expansion). It is defined as an incomplete expansion of a lung; airlessness of a lung that was once expanded; collapsed lung.1 Pneumonia will cause airlessness of a lung as well, but the primary difference is that with pneumonia the air in the alveoli is replaced by fluid causing the lung to be of normal size or to actually expand. There are several classifications of atelectasis that are helpful to understand when assessing prognosis and treatment. They can be divided into obstructive and non-obstructive causes. Obstructive atelectasis is also called resorptive atelectasis. It occurs following obstruction of a major bronchus or peripheral bronchiole with secondary resorption of the alveolar gases into the capillary bed. Collateral ventilation is obscured contributing to the collapse. Non-obstructive causes include relaxation, compression, adhesive, and cicatrization atelectasis. Relaxation atelectasis occurs secondary to a pneumothorax or pleural effusion with relaxation of the lung lobe into a deflated state to the extent of its normal elastic recoil. Compression atelectasis occurs secondary to increased intrathoracic pressure secondary to a severe pleural effusion, a tension pneumothorax, or a pulmonary mass. This will cause the lung to collapse more severely than relaxation. Adhesive atelectasis is secondary to collapse of alveoli secondary to a lack of surfactant. Cicatrization atelectasis is secondary to fibrosis of the affected lobe with subsequent lack of expansion. This generally occurs secondary to chronic airway disease. Postnatal nonexpansion of the lungs is considered atelectasis as well.
The findings in this case are impressive due to the relative lack of radiographic changes seen on the lateral view. This emphasizes the importance of orthogonal views. The atelectasis in this case is most likely due to a resorptive or a cicatrization process secondary to chronic airway disease or accumulation of secretions in the airway. A lung lobe torsion or an obstruction of a main stem bronchi by a mass or foreign body can not be excluded.2
References
- Dorland WAN. Dorland's illustrated medical dictionary. 28 ed. Philadelphia: W.B. Saunders Co., 1994;154
- Suter P, Lord P. Lower airway and pulmonary parenchymal disease. In: Suter P, ed. Thoracic Radiology, Thoracic diseases of the dog and cat.: Suter, PF, 1984;527-532.
Dr. John Feleciano, DVM, DACVR
Dr. Renee Leveille, DVM, DACVR
