Contiguous transverse images acquired with soft tissue and lung algorithms were obtained. Post-contrast images acquired with a soft tissue algorithm were also obtained.

There was increased attenuation ventrally in the right middle and caudal segment of the left cranial lung lobes. Faint air bronchograms were also seen in the right middle lobe region.

There was a more prominent increase in attenuation of the parenchyma in the ventral aspect of the cranial segment of the left cranial lobe. Adjacent to the medial aspect of this lobe, an oval structure of round margins displaying a vesicular gas pattern was seen extending from the left cranial aspect of the cardiac silhouette to the thoracic inlet, displacing the mediastinum to the right. This structure was hyperattenuating to normal lung parenchyma and displayed minimal to no contrast-enhancement. An area of increased attenuation with air bronchograms and lack of visualization of the pulmonary vasculature was present ventrally between the left cranial lobe and this structure, at the level of the 3rd rib. At this level, the cranial lobar vessels and the cranial lobar bronchus were not clearly visualized even in the contralateral normal side.

The abnormal structure described was suspected to represent a portion of the cranial segment of the left cranial lung lobe. Differential diagnoses for the vesicular gas pattern and increased volume observed in this portion of the lobe included lung lobe torsion, abscess, and necrotic neoplasia(1). Differential diagnoses for the interstitial to alveolar pattern seen in the adjacent portion of the left cranial lobe included vascular congestion, atelectasis, pneumonia or neoplasia.

The interstitial to alveolar changes seen in the ventral aspect right middle lung and caudal segment of the left cranial lobes were suspected to represent positional atelectasis and/or vascular congestion but early/mild pneumonia could not be ruled out.

Diagnosis

A left 5th intercostal thoracotomy was performed and a segmental torsion of the cranio-ventral aspect of the left cranial lung lobe was found. A partial lung lobectomy was performed. Histopathology indicated circulatory compromise consistent with a history of lung lobe torsion with no evidence of an underlying predisposing cause.  The patient recovered without complications and was asymptomatic at the 2-week recheck.

Discussion

Lung lobe torsion is an infrequent condition in dogs which occurs when a lung lobe rotates around the hilus leading to vascular congestion and airway obstruction(1). Very rarely have segmental lung lobe torsions been reported where only part of a lung lobe is affected(2) – in this case, a portion of the cranial segment of the left cranial lung lobe.

A vesicular gas pattern, or vesicular emphysema, on thoracic radiographs is well described to occur in correlation with lung lobe torsions(1-4). There are many theories as to why this pattern occurs, including as a consequence of a bronchial tear, alveolar rupture, or gas-forming infection(3). Other common radiographic patterns include pleural effusion, pneumothorax, lobar sign, abnormal orientation of the bronchus and/or lobar vessels, and displacement of structures adjacent to the affected lobe(3).

CT features of lung lobe torsion are similar to those patterns identified on radiographs. CT in particular is useful for tracing the lobar vessels and bronchus; an abruptly ending bronchus or divergent vessels are suggestive of lung lobe torsion(5).

In this case, a lung lobe torsion was suspected based on the radiographic appearance but, given the lack of additional findings such as pleural effusion and deviation of the lobar bronchus and vessels, the CT exam was used to confirm the diagnosis and location of the torsion, and to guide the surgical intervention.

Lung lobe torsions can occur spontaneously or secondary to an underlying condition including pleural effusion, after a previous lung lobectomy, due to trauma, or in association with primary lung or mediastinal disease(3). Historically, large, deep chested dogs are thought to be predisposed to spontaneous lung lobe torsion, particularly of the right medial lung lobe, while small-breed dogs tend to develop lung lobe torsion secondary to other conditions that are often associated with advanced age(2,4). Young male Pugs are described to be predisposed to spontaneous lung lobe torsion of the left cranial lung lobe which is suggested to be due to a bronchial cartilage dysplasia leading to hilar instability(4).

Prognosis for spontaneous lung lobe torsion with surgical removal of the affected lung lobe in a stable patient is excellent(4).

References

1. Agut A., Carrillo J., Seva J., Soler M. and F. G. Laredo. “What Is Your Diagnosis?” Journal of the American Veterinary Medical Association 243.3 (2013): 333-335.
2. Hofeling A., Jackson A., Alsup J. and D. O’Keefe. “Spontaneous Midlobar Lung Lobe Torsion in a 2-Year-Old Newfoundland.” Journal of the American Animal Hospital Association 40 (2004): 220-223.
3. D’Anjou M., Tidwell A. and S. Hecht. “Radiographic Diagnosis of Lung Lobe Torsion.” Veterinary Radiology and Ultrasound 46.6 (2005): 478-484.
4. Murphy, K. and B. Brisson. “Evaluation of Lung Lobe Torsion in Pugs: 7 cases (1991-2004).” Journal of the American Veterinary Medical Society 228.1 (2006): 86-90.
5. Seiler G., Schwarz T., Vignoli M. and D. Rodriguez. “Computed Tomographic Features of Lung Lobe Torsion.” Veterinary Radiology and Ultrasound 49.6 (2008): 504-508.