History
An 8-year-old 9.7-kg (21.3-lb) castrated male Dachshund was referred for evaluation because of a 3-month history of 2 subcutaneous thoracic masses and a 2-month history of intermittent vomiting, mild inappetence, and signs of back pain. Approximately 3 years before the referral examination, the dog had thoracic trauma from a coyote attack; approximately 3 months before the referral examination, the owner noticed that the dog had 2 subcutaneous masses on its thorax and took the dog to the referring veterinarian. Results of thoracic radiography at that point (not shown) included trace pleural fissure lines, lobar retraction, and the combination of wispy, soft tissue streaks and subcutaneous gas lucencies at the right sixth to eighth intercostal spaces. No aspirate samples of the masses were taken, and results of clinicopathologic analyses included a free T4 concentration and CBC within reference limits; hypocholesterolemia (122 mg/dL; reference range, 131 to 345 mg/dL), with the remainder of the serum biochemical analyses results within reference limits; and urine specific gravity within reference limits, but a urine pH of 8.0 (reference range, 5.0 to 7.0), 1+ bilirubin concentration, and 1+ ammonium magnesium phosphate concentration. Over the following 30 days, the dog had intermittent vomiting and developed signs of back pain and mild inappetence, and the dog was referred to a veterinary neurologist. The neurologist identified no neurologic abnormalities but did notice a moveable and mildly firm subcutaneous mass (approx 2-cm diameter) on the right ventral aspect of the thorax and a moveable, soft subcutaneous mass (approx 3-cm diameter) on the left side of the thorax. The neurologist found no other abnormalities on physical examination and recommended MRI to further investigate the dog's signs of back pain and recheck thoracic radiography because previous radiographic findings (eg, pleural fissure lines) could have indicated mild pleural fluid. Thoracic radiography was performed (Figure 1).
Ventrodorsal (A) and left lateral (B) thoracic radiographic images of an 8-year-old 9.7-kg (21.3-lb) castrated male Dachshund evaluated because of a 3-month history of 2 subcutaneous thoracic masses and a 2-month history of intermittent vomiting, mild inappetence, and signs of back pain. Images published with the permission of Veterinary Specialty Hospital, the copyright holder; all rights reserved. Individuals wishing to reproduce the images should contact Veterinary Specialty Hospital, 10435 Sorrento Valley Rd, San Diego, CA 92121.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.147
Formulate differential diagnoses and treatment strategies from the history, clinical findings, and Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
Thoracic radiography revealed a well-defined gas lucency in the subcutaneous tissue on the right side of the thorax at the level of the fifth to seventh intercostal spaces, rightward shift of the cardiac silhouette, rounded and retracted ventral margin of the right middle lung lobe, and striated soft tissue opacity overlying the right sixth rib (Figure 2). A diffuse bronchial and unstructured interstitial pulmonary pattern was noticed, and there was no evidence of pleural effusion. Skeletal findings (eg, spondylosis deformans and a small defect with smooth margins in the cranial endplate of T9) appeared benign and unchanged from the radiographic images obtained approximately 3 months previously (not shown). Differential diagnoses for the subcutaneous gas lucencies (more noticeable in these radiographic images than in the images obtained 3 months earlier) were subcutaneous emphysema (eg, iatrogenic or from a penetrating wound), abscess formation, necrosis, or, less commonly, lung lobe herniation. Given the cardiac shift, history of thoracic trauma, and healed injury to the sixth rib, we suspected lung lobe herniation through a long-term defect in the thoracic wall. The key differential diagnosis for diffuse bronchial pattern was inflammatory airway disease with mural thickening, peribronchial infiltrates, or bronchial calcification. To further characterize the abnormalities detected and to plan for the surgical treatment of lung lobe herniation, thoracic CT was recommended.
The same radiographic images as in Figure 1. In the subcutaneous tissue on the right side of the thorax at the level of the fifth to seventh intercostal spaces, a well-defined gas lucency (black arrows; A) is evident, consistent with lung lobe herniation. The cardiac silhouette (star; A) is shifted to the right, the appearance of which is compounded by the obliquity of patient positioning. The ventral margins of the right middle lung lobe (white arrows; B) appear rounded and retracted. A soft tissue opacity striation (circle; B) overlies the right sixth rib, and a diffuse bronchial and unstructured interstitial pulmonary pattern is evident. Images published with the permission of Veterinary Specialty Hospital, the copyright holder; all rights reserved. Individuals wishing to reproduce the images should contact Veterinary Specialty Hospital, 10435 Sorrento Valley Rd, San Diego, CA 92121.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.147
The dog underwent general anesthesia for thoracic CTa without positive pressure ventilation, and iohexol (240 mg of iodine/mL solution; 2.2 mL/kg [1.0 mL/lb]), IV; 6,900 mg total) was administered. In the right lateral aspect of the thoracic wall, an approximately 1-cm-diameter defect was identified in the fifth intercostal space and an approximately 2-cm-diameter defect was identified in the sixth intercostal space (Figure 3). The right middle lung lobe herniated through these intercostal defects and into the tissue circumferentially around the sixth rib. There was increased soft tissue attenuation (possibly representing atelectasis or fibrosis) around the bronchi and vasculature of the herniated lung lobe where it passed through the thoracic wall defects. The right sixth rib had a smoothly irregular margin, consistent with a healed rib fracture, and the most distal aspect of it near the costal arch appeared embedded in the right middle lung lobe. There was no evidence of pleural effusion, subcutaneous edema, or fluid accumulation to suggest a sudden development of the lesions identified. However, pleural thickening and subpleural opacification of the compressed and herniated lung tissue were evident and could have resulted in earlier misinterpretation as potential pleural fluid.
Dorsal reconstructed (A) and transverse (B and C) plane thoracic CT images of the dog in Figures 1 and 2 after administration of contrast medium. A herniated portion of the right middle lung lobe (white bracket; A and B) is evident as the bronchus (white arrow; B) and pulmonary artery (arrowhead; B) of the lobe traverse the thoracic wall defects (black arrows; B and C) and into the tissues around the sixth rib. The thoracic wall defects are approximately 1 cm in diameter in the fifth intercostal space (B) and approximately 2 cm in diameter in the sixth intercostal space (C). The images are at the level of the herniated right middle lung lobe (A through C) and at the levels of the fifth (B) and sixth (C) intercostal spaces parallel to the ribs. The dog's right is toward the left of each image. Images published with the permission of Veterinary Specialty Hospital, the copyright holder; all rights reserved. Individuals wishing to reproduce the images should contact Veterinary Specialty Hospital, 10435 Sorrento Valley Rd, San Diego, CA 92121.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.147
Treatment and Outcome
Right lateral thoracotomy was performed at the level of the sixth intercostal space. The right middle lung lobe was confirmed to have been external to the thoracic cavity, superficial to the fifth and sixth intercostal spaces, and adhered to the medial aspect of the sixth rib. The sixth rib was transected dorsal and ventral to the adhesions, and the right middle lung lobe was removed at the level of the hilus. Results of histologic examination of the removed lung lobe and portion of rib indicated pulmonary atelectasis and contusion, consistent with lung lobe herniation. Eleven days after surgery, the owner reported that the dog had incidences of vomiting but was otherwise eating and acting well.
Comments
Lung lobe herniation is defined as a lung lobe outside the normal boundaries of the thoracic cavity.1 It has been described in dogs with histories of trauma or chronic airway disease.2,3 The most common traumatic cause is an animal attack that results in wounds penetrating through the intercostal muscles.4 Chronic airway disease is a more insidious process with multiple predisposing factors (eg, hyperinflation, increased expiratory effort, and persistent coughing secondary to chronic obstructive airway disorders3) that may result in lung lobe herniation in the cervical and thoracic regions. Steroid use may be a contributing factor in either scenario owing to the subsequent weakening of intercostal muscles or muscles at the thoracic inlet.3
The dog of the present report had relatively nonspecific clinical signs, and lung lobe herniation was an unexpected finding on diagnostic imaging. However, lung lobe herniation could result in signs similar to those of back pain. Results of diagnostic imaging of the dog of the present report were consistent with a long-term process, given the presence of a healed rib fracture and no evidence of acute lesions. Because the dog did not have a history of coughing, it was unlikely that the dog's lung lobe herniated because of long-term increased thoracic pressure, as could occur with chronic lower airway disease. However, because the dog's history included a coyote attack, we suspected that lung lobe herniation occurred as a result of injuries received in the attack. In addition, we recognized that the attack could have caused extensive skin damage and subcutaneous emphysema that at the time could have made diagnosis of lung lobe herniation more complicated or impossible.4
Evidence of lung lobe herniation was not as apparent with thoracic radiography performed by the referring veterinarian approximately 3 months earlier as it was in our evaluation with thoracic radiography and CT. The radiographic differences between the previous and present findings may have been attributed to differences in the state of inflation of the dog's lungs for each radiographic image or to progression of herniation. A crepitus mass or a mass that changed size with respiration was not reported, and long-term, intermittent herniation of a lung lobe was less likely, given the findings consistent with a protracted condition and the intraoperative and histologic findings of adherence of the herniated lung tissue to the sixth rib. With CT, we were able to trace bronchi and vasculature of the right middle lung lobe as they passed through the thoracic wall defects at the fifth and sixth intercostal spaces. We were also able to identify pleural thickening and subpleural opacification of the compressed and herniated lung tissue, which on radiographic examination 3 months earlier could have been interpreted as pleural fluid.
Another interesting finding in the dog of the present report was that the herniated lung lobe was located circumferentially around the sixth rib. This may have resulted if the lung lobe had herniated through either the fifth or sixth intercostal space and scarred around the sixth rib, or if the sixth rib when fractured had pierced the lung lobe.2 The former scenario indicated that damage to the sixth rib at the time of attack disrupted both the fifth and sixth intercostal spaces, which could have occurred; however, evidence of a healed injury to the right fifth rib was not apparent with radiography or CT.
Overall, findings in the dog of the present report retrospectively highlighted potential difficulties in identifying damage to the thoracic wall in the presence of subcutaneous emphysema. Patients with similar findings may benefit from recheck radiographic examination after subcutaneous emphysema abates, allowing for a more thorough evaluation of the thoracic wall. Additionally, our findings underscored the resilience of patients with lung lobe herniation to survive without respiratory compromise and only show nonspecific signs.
Footnotes
Aquillin 64 slice, Canon Medical Systems Corp, Tustin, Calif.
References
1. Risselada M. Perforating cervical, thoracic, and abdominal wounds. Vet Clin North Am Small Anim Pract 2017;47:1135–1148.
2. Shaw SR, Rozanski EA, Rush JE. Traumatic body wall herniation in 36 dogs and cats. J Am Anim Hosp Assoc 2003;39:35–46.
3. Guglielmini C, De Simone A, Valbonetti L, et al. Intermittent cranial lung herniation in two dogs. Vet Radiol Ultrasound 2007;48:227–229.
4. Cabon Q, Deroy C, Ferrand FX, et al. Thoracic bite trauma in dogs and cats: a retrospective study of 65 cases. Vet Comp Orthop Traumatol 2015;28:448–454.
