Spontaneous Midlobar Lung Lobe Torsion in a 2-Year-Old Newfoundland

Case Report

A 54.4-kg, 2-year-old, intact male Newfoundland was referred for evaluation of a 1- to 2-day history of coughing, retching, and progressive lethargy. Prior to presentation, a complete blood count (CBC), serum biochemical profile, thoracic radiographs, and an electrocardiogram (ECG) were completed by the referring veterinarian. The results of the CBC and serum biochemical profile were unremarkable. Referral radiographs revealed an area of increased radiopacity in the right caudal thorax and right-sided pleural effusion. The ECG demonstrated a sinus tachycardia with small QRS complexes. Differential considerations for the tachycardia included stress, excitement, and shock secondary to primary intrathoracic disease. The small QRS complexes were attributed to the presence of pleural fluid.

At presentation, the dog was ambulatory but severely depressed. No episodes of coughing or retching were noted. Upon physical examination, the dog was in good body condition. Mucous membranes were pink, and capillary refill time was <1 second. Auscultation of the thorax revealed moderate tachycardia (120 beats per minute), tachypnea (44 breaths per minute), and diminished bronchovesicular sounds caudoventrally on the right side. No abnormalities were noted upon auscultation of the left pulmonary fields. No cough was elicited with tracheal palpation. Femoral pulses were strong and synchronous. The remainder of the physical examination was unremarkable.

Results of the physical examination and initial diagnostics were consistent with primary intrathoracic disease resulting in a region of increased radiopacity and pleural effusion. Differential diagnoses included diaphragmatic hernia, pulmonary contusion, lung lobe torsion, neoplasia, and pulmonary consolidation or atelectasis. A packed cell volume/total solids (PCV/TS) evaluation, thoracocentesis, and abdominal and thoracic radiography were performed to further differentiate the dog’s underlying disease.

Thoracocentesis yielded 170 mL of a nonclotting, hemorrhagic effusion that had a PCV of 19%. Cytopathology was performed on the fluid. Results were consistent with a hemorrhagic effusion, with red blood cells being the predominant cell type. A small number of nondegenerate neutrophils, macrophages, and reactive mesothelial cells were also present in the fluid. No neoplastic cells or bacterial organisms were noted. The peripheral PCV and TS were normal at 39% (reference range, 37% to 55%) and 6.0 g/dL (reference range, 5.5 to 7.5 g/dL), respectively. A prothrombin time (PT) and an activated partial thromboplastin time (PTT) were submitted to rule out a coagulopathy and were normal. Prothrombin time was 7.7 seconds (reference range, 6.0 to 12.0 seconds); PTT was 15.8 seconds (reference range, 10.0 to 25.0 seconds). Abdominal radiographs showed normal distribution of the abdominal contents, an intact diaphragm, and no evidence of abdominal effusion.

Thoracic radiographs [Figures 1A, 1B] were repeated following thoracocentesis. Radiographs showed an alveolar pattern involving what was suspected to be the right middle or right caudal lung lobe. On both radiographic views, one portion of lung in the right hemithorax was unusual in that it contained multiple, interrupted, 1- to 3-mm pockets of gas. The mottled gas pattern (i.e., vesicular emphysema) was thought to be associated with a caudally displaced right middle lung lobe. Pleural fluid was sequestered on the right side of the thorax, based upon retraction of the right cranial lung lobe from the thoracic wall and the prominence of pleural fissure lines on the ventrodorsal radiograph. Differential considerations at this time included lung lobe torsion, neoplasia, atelectasis, pneumonia, infarction, or a diaphragmatic hernia.

Based upon clinical findings, an exploratory thoracotomy was recommended to further evaluate the vesicular emphysematous structure and the source of hemorrhage within the right thoracic cavity. Morphine (0.5 mg/kg intra-muscularly [IM]) was given preoperatively. Anesthesia was induced with diazepam (0.5 mg/kg intravenously [IV]) and ketamine (10 mg/kg IV). The dog was intubated and maintained with isoflurane in oxygen. During the procedure, the dog was mechanically ventilated. The dog received cefazolin (22 mg/kg IV) at the time of induction, and the cefazolin was repeated at 2-hour intervals during surgery.

A right-sided, fifth intercostal thoracotomy was performed. A standard approach to the right hemithoracic cavity was made through the fifth intercostal space. Upon entering the thoracic cavity, approximately 800 mL of hemorrhagic effusion was removed via suction. Exploration of the right hemithorax revealed lung lobe torsion in the mid-lobar region of the right caudal lung lobe [Figure 2]. A partial lung lobectomy was performed using a thoracoabdominal stapling device^a to remove the diseased portion of the right caudal lung lobe. No additional abnormalities were noted on the exploratory surgery. A 14-French chest tube^b was placed prior to closure. The thoracic wall and skin were closed routinely, and bupivacaine^c (0.5 mg/kg) was infused through the chest tube to provide local anesthesia. A nasal oxygen catheter was placed to provide supplemental oxygen during the recovery period. The resected tissues were submitted for histopathology.

Postoperatively, the dog recovered without complications. Supportive care was continued with IV fluids, a constantrate infusion of morphine (0.1 mg/kg per hour IV), and supplemental oxygen. A transdermal fentanyl patch^d (100 μg per hour) was applied for additional analgesia. The chest tube was aspirated q 4 hours. Following each aspiration, bupivacaine^c (0.5 mg/kg) was infused through the chest tube. The chest tube was removed approximately 24 hours postoperatively when there was no production of fluid and air for 8 consecutive hours. The IV fluids and morphine were decreased over the next 36 hours, and the dog was discharged with the fentanyl patch in place. Oral acetaminophen-codeine^e (2.2 mg codeine/kg q 6 to 8 hours as needed) was prescribed for additional pain control.

The dog continued to recover without incident and was asymptomatic at his 2-week recheck. Thoracic radiographs repeated at that time showed complete resolution of the pleural effusion. Histopathology results were consistent with hemorrhage, inflammation, and thrombosis secondary to the lung lobe torsion.

Discussion

Lung lobe torsions have been reported infrequently in dogs and cats.^1–10 Large-breed dogs with a deep, narrow chest are predisposed to spontaneous lung lobe torsions; however, spontaneous torsions have recently been reported in two Chinese pugs.^12458–10 Lung lobe torsions can occur in small-breed dogs and cats but are often associated with a predisposing condition such as pleural effusion, trauma, diaphragmatic hernia, or prior surgery.^1–58–10 The right middle lung lobe is the most common lobe affected because of its increased mobility associated with its long, narrow shape and short pedicle.^12458–10 All lung lobes may be affected individually or in combination with additional lobes.^1–10 By definition, lung lobe torsion has historically been described as a rotation of the lung lobe along its long axis, with twisting of the bronchus and vessels at the hilus.²⁵⁹ During typical torsions, the muscular walled arteries often remain partially patent and allow persistent arterial blood flow to the affected lobe. This leads to venous congestion and consolidation of the torsed lobe.¹²⁴⁵⁸⁹ This consolidation appears as an opacified lung lobe with or without air bronchograms, and it is the most common radiographic finding.^124–9

This case is unusual in that a spontaneous torsion occurred at the midlobar region of the right caudal lung lobe. To the authors’ knowledge, this has not been previously reported. One prior case was identified where torsion had occurred at a point other than its hilus. The case involved a 5-month-old chow chow with a left cranial lung lobe torsed secondary to underlying congenital pulmonary pathology.³ Whereas congenital pulmonary pathology was present in the case involving the chow chow, results of histopathology in the case reported here showed no evidence of preexisting disease. Newfoundlands fit the criteria of a deepchested, large-breed dog, but they have not been previously reported in the literature as being affected by lung lobe torsion. Additionally, this torsion affected the right caudal lung lobe, which is extremely uncommon and has only been reported twice.²¹⁰

Radiographically, this case was a diagnostic challenge. The radiographic appearance of the mottled gas pattern was atypical of lung lobe torsion. A similar pattern has been previously reported on two occasions with lung lobe torsions.³¹⁰ Both cases involved young dogs (5 and 6 months of age), one of which had an underlying pulmonary pathology.³¹⁰ The thoracic radiographic pattern in this case mimicked that of ingesta or fecal contents, raising the suspicion of a diaphragmatic hernia. Normal abdominal radiographs were not compatible with a diaphragmatic hernia, so the abnormal pattern was considered to be thoracic in origin. Two possible modes of pathophysiology may explain this radiographic appearance. First, it is theorized that the mottled gas pattern may have been secondary to air trapped within the alveoli and that because of the acute presentation, not enough time had elapsed for complete consolidation to occur. Also, because of the location of the torsion, some vessels and bronchioles may have been protected from complete obstruction by the surrounding pulmonary parenchyma. This may have prevented complete occlusion of all vessels and smaller airways and allowed some blood and air to move in and out of the torsed lung lobe. These radiographic changes may be a common finding in midlobar torsions, but their actual incidence remains unknown until additional cases are reported.

Conclusion

This case demonstrated that lung lobe torsions can occur at a point other than the hilus without the presence of underlying pulmonary pathology. The thoracic radiographs revealed a very unusual pulmonary pattern, which may be indicative of midlobar lung lobe torsions. With recognition of this radiographic pattern, lung lobe torsion should be included as a differential diagnosis. Ultimately, an exploratory thoracotomy was diagnostic and was also the therapeutic tool of choice in this case.

Acknowledgments

The authors thank Dr. Justin M. Goggin, Diplomate ACVR, with Metropolitan Veterinary Radiology, Ltd., Montclair, New Jersey, for reviewing the radiographs in this case.