Signalment & History
A 3.5 year old FS Teacup Yorkshire Terrier presents for respiratory distress. Owner reports that today she started coughing excessively, gagging and having severe difficulty breathing. He said she usually begins coughing and gagging when she gets excited or when he walks her and outside it’s particularly hot. On physical examination, Lizzie has pink mucous membranes, CRT <2 sec, RR 36 bpm at rest, 60 bpm when excited, HR 144 bpm, 102.2 °F, no murmur and strong synchronous pulse. She has increased bronchovesicular sounds in all lung fields, moderate to severe respiratory effort and dry, harsh, high-pitched cough on tracheal palpation.
Findings
At the level of the thoracic inlet, a nearly completely collapsed cranial thoracic trachea is noted on both lateral projections. The tracheal margins at this level are undulant and irregular. An associated fusiform soft tissue opacity is seen at the level of the thoracic inlet, superimposed along the dorsal tracheal wall. Additionally, there is a mild straightening of the caudal margin of the cardiac silhouette, representing left atrial enlargement, and increase length of the cardiac silhouette in the lateral projections, dorsally displacing the trachea, compatible with left ventricular enlargement. The pulmonary vasculature is within normal limits. The caudoventral margin of the liver extends beyond the costal arch and has rounded margins. Additionally, the spleen is moderately enlarged and rounded.
Diagnosis
You have found a nearly completely collapsed cranial thoracic trachea. In addition you noted a mild straightening of the caudal margin of the cardiac silhouette, representing left atrial enlargement, and increase length of the cardiac silhouette in the lateral projections, dorsally displacing the trachea, compatible with left ventricular enlargement. Furthermore, you saw a mild enlargement of the liver, extending beyond the costal arch, with rounded caudoventral margins. Also, you found a moderate enlargement of the spleen. These radiographic abnormalities are consistent with: static, extrathoracic tracheal collapse with associated redundant tracheal membrane; mild, left sided cardiomegaly (mitral endocardiosis is the primary differential); mild generalized hepatomegaly (considerations include vacuolar hepatopathy, regeneration, or infiltrative neoplasia), and mild generalized splenomegaly (differentials include congestion, extramedullary hematopoiesis, hyperplasia or infiltrative neoplasia).
Conclusions
Tracheal collapse (with chondromalacia) is typically characterized by dorsoventral flattening of the tracheal rings and prolapse of the tracheal membrane into the lumen. Collapse can be static or dynamic and can occur anywhere from the midcervical region to involving the entire thoracic trachea. Attention should be paid to the mainstem bronchi, which are often involved, along with tracheal collapse or as the sole abnormality. Intrathoracic collapse is generally more pronounced on expiration, whereas extrathoracic collapse (cervical and thoracic inlet regions) is more pronounced on inspiration. Complete airway obstruction during expiration reduces the volume of the thoracic cavity while pulmonary volume is mantained and may lead to a dynamic paradoxical cranial or telescopic movement of the thoracic trachea, along with herniation of cranial lung lobes into the thoracic inlet. Static tracheal collapse can be seen on survey lateral radiographs of the thorax and cervical region as a persistent narrowing of the tracheal lumen. However, even when collapse is not noted, an undulating appearance of the tracheal wall associated with mild variation in lumen diameter are suggestive of chondromalacia. Fluoroscopy is suggested to rule out mainstem bronchi involvement and to better evaluate the tracheal diameter over several normal respiratory cycles followed by evaluation during induced cough. Location and extent of maximal collapse is evaluated using a scale similar to the one used at bronchoscopy (25%, 50%, 75%, and 90 % to 100% reduction of tracheal diameter). A minimal reduction (25% or less) during the respiratory cycle is considered normal.
Tracheal collapse and chondromalacia are commonly noted in middle-aged to older miniature, toy and small breed dogs. Yorkshire terriers, Pomeranian, Pugs, Poodle, Maltese and Chihuahua are overrepresented breeds. About 25% of the affected dogs show clinical signs by the age of 6 months. When the principal bronchi are also involved the condition is called tracheobronchomalacia. Bronchomalacia is reported in 45-83% of dogs with tracheal collapse. Collapse of the left cranial and right middle lobar bronchi are the most commonly reported in dogs. These affected patients typically have chronic cough but signs of upper respiratory obstruction can occur in severely affected dogs. Characteristic paroxysmal or waxing and waning respiratory signs are often reported, mostly described as a dry, harsh, or “honking” (“goose-honk”) cough. Worsening tachypnea, exercise intolerance, and respiratory distress are exacerbated by physical exertion, excitement, drinking or eating, pulling on a leash with a neck lead, heat stress or humid conditions. Cyanosis and syncope can also occur. Performing a lateral radiograph of the thorax and cervical region in both the expiratory and the inspiratory phases is recommended. Fluoroscopy is used to better assess the extent and location of the airway collapse. Bronchoscopy is considered the gold standard for diagnosis of bronchomalacia in humans. Dogs presenting in respiratory distress are a medical emergency and stabilization should always precede any diagnostic test. When medical management is no longer effective to control clinical signs, surgical intervention or placement of an intraluminal stent should be considered. Postoperative complications include bacterial tracheitis, stent fracture/migration, development of obstructive granulation tissue, laryngeal paralysis and tracheal necrosis.
References
Tracheal and Airway Collapse in Dogs. Ann Della Maggiore. Vet Clin Small Anim (44) 2014 117-127.
