Feline imaging self-assessment
Shuki, an 11-month-old neutered male cross-breed dog, went missing for two days. When he was found he was in a poor state – panting heavily, lethargic, anorectic and with extensive bruising of the right thoracic wall and axilla. The owner noted two bouts of vomiting.
When Shuki was admitted to our emergency unit he was lethargic and showed moderate tachypnoea. Capillary refill time was within normal range (2 seconds) and he was febrile (rectal temperature 40°C). Thoracic auscultation revealed tachycardia, pulmonary wheezing in the right hemithorax and tachypnoea. Blood chemistry and abdominal palpation were unremarkable. Haemogram revealed moderate leukocytosis and neutrophilia with a left shift. There was soft tissue swelling over the right hemithorax and axilla and the skin was bruised but not torn.
Radiographs of the thorax were taken with the dog in right lateral and dorsal recumbency (Figs. 1a and 1b).
- 1Describe the abnormalities you can see on the thoracic radiographs.
- 2What would be your main differential diagnoses given the radiographic findings?
- 3What further imaging would you like to perform in this case to confirm your diagnosis?
1. There is soft tissue swelling at the region of the right thoracic wall and axilla associated with multiple air pockets tracking into the subcutaneous space in the region of the right hemi-thorax, sternum and dorsally to the thoracic spinous processes (subcutaneous emphysema). Laterally and adjacent to the right thoracic wall (ribs 4–8) there is a subcutaneous, pear-shaped (balloon-like), air-filled structure which is well demarcated by a thin rim. The structure appears hyperlucent with fine, branching, linear, tree-like structures emanating from a common origin at roughly rib 4–5 space.
The soft tissue of the right thoracic wall is slightly irregular with loss of the smooth outline of the fascial planes, suggestive of soft tissue trauma.
There is a small, wedge-shaped, soft tissue opacity separating the right middle and cranial lung lobes, suggestive of focal accumulation of pleural effusion. The right middle lobe appears to be hyperlucent and bulging (subtle observation).
2. Possible differentials for such findings are:
- • herniated, partially entrapped or torsed right middle lung lobe
- • herniated large pulmonary bulla or bleb
- • large subcutaneous emphysematous pocket.
Due to the internal linear markings (representing pulmonary blood vessels) and well-defined thin rim, a herniated right middle lung lobe is most likely. The observation of a hyperlucent bulging right middle lung lobe within the thorax is suggestive of a degree of torsion leading to air trapping. The subcutaneous emphysema may be caused by trauma such as a bite, extension of pneumomediastinum or pneumothorax via fascial planes or intercostal hernia of gas-filled structures (e.g. lung, bowel).
3. Computed tomography (CT) is the examination of choice for further assessment of the patient and surgical planning. It is a quick and non-invasive procedure which can be performed safely on the trauma patient using light sedation. CT produces cross sectional images of the thorax, therefore superimposition of thoracic structures do not pose any diagnostic pitfall. Furthermore, images can be reconstructed in any planes (e.g. sagittal, dorsal) and assessed in different window levels (e.g. bone, lung, soft tissue) at superior spatial and contrast resolution, leading to increased tissue definition.
The CT images (Figs. 2a and 2b) clearly depict a herniated right middle lung lobe through a slit-like opening between the fourth and fifth ribs. Both herniated and intrathoracic parts of the right middle lung lobe were hyperinflated (hyperlucent and bulging), suggestive of air trapping and possibly a degree of lung lobe torsion at the base. There was evidence of a small-volume pneumothorax and pleural effusion, mostly in the right hemithorax.
During surgery, it was confirmed that the right middle lung lobe had herniated through a slit-like traumatic muscular defect between ribs four and five. The entire lobe was rotated 180° along its longitudinal axis. The lobe appeared intact, therefore the gap between the ribs was extended and the lobe was replaced into the thorax. There was no evidence of leakage so the gap was closed and the dog admitted to the intensive care unit.
Shuki made a good recovery from surgery and was discharged the following day.