IMAGING DIAGNOSIS—ACQUIRED PECTUS EXCAVATUM SECONDARY TO LARYNGEAL PARALYSIS IN A DOG TSUMUGI ANNE KUROSAWA, JEFFREY D. RUTH, JEFFREY STEURER, BRENDA AUSTIN, HOCK GAN HENG
A 13-year-old neutered female Labrador retriever had inspiratory dyspnea secondary to bilateral laryngeal paralysis. Radiographically, there was pectus excavatum with a mediastinal shift to the right. Arytenoid lateralization was performed, relieving the upper respiratory obstruction, and the sternal deformity also resolved. Chronic upper respiratory obstruction should be considered in dogs with pectus excavatum. Furthermore, corC 2011 rection of upper respiratory obstruction has the potential to result in resolution of pectus excavatum. Veterinary Radiology & Ultrasound, Vol. 00, No. 0, 2011, pp 1–4. Key words: dog, laryngeal paralysis, pectus excavatum, radiography.
Signalment, History, Clinical findings
and a small smoothly marginated gas bubble was located in the intersternebral space. The mediastinum and heart were shifted to the right. There was cranial displacement of the cupula of the diaphragm. The findings indicate pectus excavatum, leading to displacement of the heart to the right. The sternal position was thought to be either acquired, secondary to laryngeal paralysis, or congenital.
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13-YEAR-OLD, NEUTERED FEMALE, Labrador retriever had a 1-year history of progressive inspiratory dyspnea and respiratory noise. The patient had undergone a leftsided arytenoid lateralization after diagnosis of bilateral laryngeal paralysis. The dog was dyspneic, with cyanosis and inspiratory stridor. There was not a palpable abnormality of the thoracic wall or dynamic sternal position throughout the respiratory cycle. Low oxygen saturation was present, presumed due to hypoventilation, and nasal oxygen was administered. There was mild normocytic, normochromic anemia, and a stress leukogram. There was also bilateral laryngeal paralysis with suspected breakdown of the previous left arytenoid lateralization. Surgical lateralization of the right arytenoid was recommended.
Diagnosis/Outcome Lateralization of the right arytenoid was performed successfully. Thoracic radiographs were acquired 3 days later, prior to discharge from the hospital (Fig. 2). The position of the sternum and diaphragm was normal. The patient was discharged, and no postoperative complications were noted.
Imaging
Discussion
In presurgical thoracic radiographs, there was dorsal deviation of the fourth through eighth sternebrae and costal cartilages, resulting in narrow dorsoventral thoracic dimension (Fig. 1). The frontosagittal index was increased, at 2.3, indicative of moderate pectus excavatum (Normal = 1.09; 95% CI: 1.04–1.14).1 The sternum remained displaced dorsally on multiple views. Mild new bone formation surrounded the articulation of the fourth and fifth sternebrae,
In people, pectus excavatum is posterior displacement of the sternum and costal cartilages, which results in axial cardiac rotation and a shift of the heart to the left.2, 3 Congenital and acquired forms of pectus excavatum have been described. The congenital form is more common in males and is the most frequent chest wall deformity, accounting for over 87% of all chest deformities.3–5 While approximately 40% of patients with pectus excavatum have a family member with the condition, a precise genetic link has not been identified.6 A variety of factors are suspected to play a role in the pathogenesis of congenital pectus excavatum, including overgrowth of the costal cartilages,2 intrauterine pressure abnormalities,7 short central tendon of the diaphragm,7 and connective tissue disorders such as Marfan syndrome and Ehlers-Danlos syndrome.5 While the incidence is unknown, acquired pectus excavatum is reported in children secondary to chronic upper airway
From the Department of Veterinary Clinical Sciences, Purdue University School of Veterinary Medicine, West Lafayette, IN 47907 (Kurosawa, Ruth, Steurer, Austin, Heng), School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803 (Kurosawa), Southwest Veterinary Surgical Services, Glendale, AZ 85306 (Steurer), and Dogs and Cats Veterinary Referral, Bowie, MD 20715 (Austin). Address correspondence and reprint requests to Jeffrey D Ruth, at the above address. E-mail:
[email protected]
Received July 14, 2011; accepted for publication October 31, 2011. doi: 10.1111/j.1740-8261.2011.01898.x
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FIG. 1. (A) Right lateral view thoracic radiograph. There is pectus excavatum with a dorsally displaced sternum. (B) On the ventrodorsal view, a mediastinal shift to the right is apparent. The diaphragm is positioned cranially on both projections.
obstruction due to tonsillar or adenoid enlargement or laryngeal malformation.8, 9 The reported cardiac and pulmonary effects of pectus excavatum depend on the severity and duration of the disease.5 Infants are often asymptomatic at the time of diagnosis; however, uncorrected pectus excavatum can progress slowly to impact cardiopulmonary function as the patient ages, resulting in dyspnea, wheezing, tachycardia, and exercise intolerance.3, 5 Cardiac effects include decreased cardiac output,10 mitral valve prolapse,11 and arrhythmias.5, 11 Pulmonary effects include restrictive lung disease, atelectasis, pulmonary infections, and paradoxical respiration in more severe forms of the disease.5 A number of surgical
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FIG. 2. (A) Right lateral and (B) ventrodorsal views acquired 72 hours after arytenoid lateralization. Note the normal position of the diaphragm and sternum, in addition to resolution of the mediastinal shift.
techniques have been described to correct congenital pectus excavatum, and surgical intervention has been shown to improve cardiopulmonary function.4, 11, 12 There are infrequent reports of surgical intervention to address acquired pectus excavatum in people, aimed at relieving the underlying upper respiratory obstruction by removing enlarged tonsils or adenoids or performing laryngoplasty.8, 9 Failure to recognize that pectus excavatum could represent a reversible sign of upper respiratory disease has resulted in delayed diagnosis of the underlying problem.9 Pectus excavatum affects a number of animal species, including dogs.13–16 The deformity has been reported in
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multiple affected dogs within a litter, suggesting possible heritability.1, 13, 17 In contrast to the current patient, the diagnosis is usually made within the first week of life.18 Analogous to human pectus excavatum, the costal cartilages are malformed and the sternum is displaced dorsally, contributing to pulmonary underinflation and usually a mediastinal shift to the left.18 Occasionally, the heart shifts to the right, as in this dog.18 The incidence or gender predisposition for pectus excavatum in the dog is not known, but brachycephalic breeds may be overrepresented.16 In eight dogs with pectus excavatum, six (75%) were brachycephalic.18 Chronic upper airway obstruction is speculated as a mechanism for acquired pectus excavatum in dogs, despite the fact that only congenital forms have been documented.16, 18 The apparent overrepresentation of brachycephalic breeds suggests that inspiratory may result in negative intrapleural pressure, contributing to acquired deformation of the costal cartilages and sternal displacement during early development. The dog in this report had chronically increased respiratory effort due to upper airway obstruction, a condition that could result in similar changes to the thoracic wall in a mature dog. While some dogs are asymptomatic, clinical signs vary depending on the severity of the dorsal displacement of the sternebrae.17, 18 Similar to people, dogs that are symptomatic develop cardiopulmonary dysfunction leading to dyspnea, cyanosis, exercise intolerance, coughing, and cardiac murmurs.16, 18, 19 Cardiac signs have been attributed to abnormal heart position, kinking of blood vessels, and mechanical compression of the heart resulting in dynamic right ventricular outflow tract obstruction.16, 19, 20 Respiratory signs in congenital pectus excavatum are presumed to be due to pulmonary displacement leading to decreased ventilation.16 Abnormalities of the thoracic wall, including rib fracture and flail sternum, have been reported in dogs and cats with chronic increased respiratory effort.21 The sternal changes noted in this dog could be the result of increased respiratory effort, as well as contributing to hypoventilation by compromising the bellows function of the thoracic wall.21
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Although there are few reports evaluating the benefit of treating congenital pectus excavatum in dogs, cardiac and respiratory function improvements have been reported after external or internal splinting.19, 22 There have been no previous reports of successful surgical treatment of acquired pectus excavatum secondary to chronic upper respiratory obstruction in the dog. In this dog, chronic upper respiratory obstruction resulted from the arytenoid cartilages remaining in a paramedian position during inspiration, creating an abnormally narrow rima glottidis. In severe laryngeal paralysis, the arytenoids can be drawn together during inspiration in a phenomenon known as paradoxical movement. The effect is to completely close the larynx during inspiration. Given the signalment in this dog, the sternal displacement was an unexpected radiographic finding that was not severe enough to be detectable on physical examination. The fact that the sternal displacement was not dynamic may have allowed this finding to go unnoticed prior to radiography. Objective radiographic classification of pectus excavatum can be determined in dogs using either the frontosagittal index or vertebral index, permitting categorization as mild, moderate, or severe.1, 16 The frontosagittal index is a ratio defined as the width of the thorax at the level of T10 on a ventrodorsal projection divided by the distance between the ventral aspect of T10 and the nearest sternebrae. The dog in this report had an increased frontosagittal index prior to arytenoid lateralization, indicative of moderate pectus excavatum. Subsequent to surgery, the frontosagittal index returned to normal, demonstrating the reversibility of the thoracic wall change. This report is unusual, in that a nonbrachycephalic dog presented at maturity with pectus excavatum, and the sternal deformity resolved after unilateral arytenoid lateralization for laryngeal paralysis. Chronic upper respiratory obstruction can cause important alterations of the thoracic wall, and should be considered in mature dogs presenting with pectus excavatum. Furthermore, correction of the upper respiratory obstruction has the potential to result in resolution of pectus excavatum.
REFERENCES 1. Fossum TW, Boudrieau RJ, Hobson, HP. Pectus excavatum in eight dogs and six cats. JAAHA 1989;25:595–605. 2. Jeung MY, Gangi A, Gasser B, et al. Imaging of chest wall disorders. Radiographics. 1999;19:617–637. 3. Jaroszewski D, Notrica D, McMahon L, Steidley DE, Deschamps C. Current management of pectus excavatum: a review and update of therapy and treatment recommendations. J Am Board Fam Med 2010;23:230–9. 4. Iida H. Surgical repair of pectus excavatum. Gen Thorac Cardiovasc Surg 2010;58:55–61. 5. Goretsky MJ, Kelly RE, Croitoru D, Nuss D. Chest wall anomalies: pectus excavatum and pectus carinatum. Adolesc Med 2004;15:455-471.
6. Fokin AA, Steuerwald NM, Ahrens WA, Allen KE. Anatomical, histologic, and genetic characteristics of congenital chest wall deformities. Semin Thorac Cardiovasc Surg 2009;21:44–57. 7. Brown AL. Pectus excavatum (funnel chest): anatomic basis; surgical treatment of the incipient stage in infancy; and correction of the deformity in the fully developed stage. J Thorac Surg 1939;9:164–184. 8. Olsen KD, Kern EB, O’Connell EJ. Pectus excavatum: resolution after surgical removal of upper airway obstruction. Laryngoscope 1980;90:832– 837. 9. Fan L, Murphy S. Pectus excavatum from chronic upper airway obstruction. Am J Dis Child 1981;135:550–552.
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10. Zhao L, Fenberg MS, Gaides M, Ben-Dov I. Why is exercise capacity reduced in subjects with pectus excavatum? J Pediatr 2000;136:163–167. 11. Kelly RE, Goretsky MJ, Obermeyer R, et al. Twenty-one years of experience with minimally invasive repair of pectus excavatum by the Nuss procedure in 1215 patients. Ann Surg 2010;256:1072–1081. 12. Robicsek F. Surgical treatment of pectus excavatum. Chest Surg Clin N Am 2000;10:277–296. 13. Ellison, Halling KB. Atypical pectus excavatum in two Welsh terrier littermates. J Small Anim Prac 2004;45:311–314. 14. Sedgwick CJ. Pectus excavatum u a douc langur (pygathrix nemaeus): one reason for managing genetic variation in zoo animal breeding programs. J Zoo Anim Med 1981;12:124–127. 15. Benirschke K, Kumamoto AT, Bogart MH. Congenital anomalies in lemur variegates. J Med Primatol 1981;10:38–45. 16. Boudrieau RJ, Fossum TW, Hartsfield SM, Hobson HP, Rudy RL. Pectus excavatum in dogs and cats. Comp Contin Educ Small Anim Pract 1990;12:341–355.
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17. Rahal SC, Morishin Filho MM, Hatschbach E, Machado VM, Aptekmann KP, Corrˆea TP. Pectus excavatum in two littermate dogs. Can Vet J 2008;49:880–884. 18. Pearson, J. Pectus excavatum in the dog. Vet Med/Small Anim Clin 1973;68:125–128. 19. Gifford AT, Flanders JA. External splinting for treatment of pectus excavatum in a dog with right ventricular outflow obstruction. J Vet Cardiol 2010;12:53–57. 20. Fournier TE. Dynamic right ventricular outflow tract (infundibular) stenosis and pectus excavatum in a dog. Can Vet J 2008;49:485– 487. 21. Hardie EM, Ramirez O, Clary EM, et al. Abnormalities of the thoracic bellows: stress fractures of the ribs and hiatal hernia. J Vet Intern Med 1998;12:279–287. 22. Fossum TW, Boudrieau RJ, Hobson HP, Rudy RL. Surgical correction of pectus excavatum, using external splintage in two dogs and a cat. J Am Vet Med Assoc 1989;196:91–97.
