Pectus excavatum in two littermate dogs

Abstract

One male and 1 female, 8-week-old, schnauzer littermates were presented with moderate and mild pectus excavatum, respectively. External application of a coaptation splint to the ventral aspect of the thorax was used for correction of the sternal deformity in the male; conservative treatment was used in the female.

An 8-week-old, 1.6-kg, intact-male schnauzer dog (case 1) was referred to the veterinary hospital for evaluation of respiratory distress, present since birth, and ventral chest wall deformity, observed at 5 wk of age. The owner also reported that 2 other littermates had had a more severe abnormality and had died; and that another littermate showing less sternum depression was still alive (case 2). The sire and dam did not show any abnormality.

Case descriptions

Case 1

Physical examination revealed marked inward deformity of the caudal half of the ventral thorax, and severe respiratory distress that became more intense when the dog was placed in dorsal recumbency. On thoracic auscultation, the heart sounds were heard on the right side of the thorax. An electrocardiogram (ECG) showed right-axis deviation and sinusal rhythm. Thoracic ventrodorsal and lateral radiographs revealed moderate sternal deviation toward the spine from the 5th sternebra caudally and a right-side displacement of the heart (Figures 1a and 1b). The frontosagittal index (ratio between width of the chest at the level of the 10th thoracic vertebra and the distance between the center of ventral surface of the 10th thoracic vertebral body and the nearest point on the sternum) and vertebral index (ratio between the distance from the center of the dorsal surface of the 10th vertebral body to the nearest point on the sternum and the dorsoventral diameter of the vertebral body at the same level) (1) were 2.0 and 9.8, respectively. Pectus excavatum was diagnosed, and external application of a coaptation splint to the ventral aspect of the thorax was planned to correct the sternal deformity. Preoperatively, a U-shaped plastic splint was contoured to the shape of a normal ventral thorax. After premedication with morphine sulfate (Dimorf; Cristália, Itapira, Brazil), 0.5 mg/kg body weight (BW), IM, anesthesia was induced with propofol (Propovan; Cristália, Itapira, Brazil), 4 mg/kg BW, IV, followed by endotracheal intubation, and maintained with isoflurane (Isoforine; Cristália, Itapira, Brazil) in controlled ventilation. Body temperature was maintained by using a heating pad, and warm Ringer’s solution was administered IV throughout the surgical procedure. The dog was positioned in dorsal recumbency and the ventral and lateral aspects of the thorax were prepared aseptically for surgery. Four sutures of size 0 polypropylene were placed percutaneously around the sternum at the depressed portion and 1 suture was placed cranially around the unaffected part of the sternum. The taper-point needle was kept close to the sternum during its passage. Suture ends were passed through predrilled holes made in the splint and tied after the sternum had been pulled up against the splint. The edges of the splint were padded. Amoxicillin (Amoxil; GlaxoSmithkline, Rio de Janeiro, Brazil), 20 mg/kg BW, PO, q12h, was administered prior to surgery and for 20 d post surgery. Meloxicam (Maxican; Ouro Fino, Ribeirão Preto, Brazil), 0.1 mg/kg BW, PO, q24h, was administered for 5 d postoperatively. A bandage was applied lightly to cover the splint and changed every 5 d. The clinical signs improved substantially after the operation. The splint and sutures were removed after being in place for 20 d. The dog tolerated the splint well and no complications were observed. After removal of the splint, normal thoracic depth was observed by physical and radiographic examinations (Figures 1c and 1d). Frontosagittal and vertebral indices were 1.3 and 13.5, respectively. The heart was still displaced to the right side.

Figure 1.

Lateral and ventrodorsal radiographic views of case 1. Notice the right-side displacement of the heart (a) and marked dorsal displacement of the caudal sternebrae (b) before surgery. Immediately after splint removal (c,d), the deformity was corrected, but the heart displacement was maintained.

The dog was reexamined 2.4 y after surgery. No apparent respiratory problem was observed. However, the dog had systemic hypertension (210 mmHg). On urinalysis, the urine was of low density (specific gravity 1.006) and had an alkaline pH (8.0). Results of serum biochemical analyses indicated low total protein (41 g/L; reference range: 51 to 78 g/L) and low albumin (18.7 g/L; reference range: 26 to 43 g/L) concentrations. An ECG revealed right-axis deviation, sinus tachycardia, increased T-wave amplitude, enlarged P-waves, and ST-segment elevation. An echocardiogram showed mild eccentric left ventricle hypertrophy with normal cardiac function. Thoracic radiographs revealed no deformity in the sternebrae and normal positioning of the heart (Figure 2). The frontosagittal and vertebral indices were 1.21 and 19.5, respectively.

Figure 2.

Lateral and ventrodorsal radiographic views of case 1, 2.4 y postoperatively. Notice the normal position of the sternum and heart (a,b).

Case 2

An 8-week-old, 2.1-kg, intact-female schnauzer dog (case 2), littermate of case 1, was presented with mild dorsal deviation of the caudal part of the sternum and occasional signs of respiratory distress after exercise. Thoracic auscultation and an ECG were normal. Thoracic ventrodorsal and lateral radiographs revealed dorsal deviation of the caudal part of the sternum, beginning at the 6th sternebra, and heart displacement to the left (Figures 3a and 3b). The frontosagittal index was 1.7, and the vertebral index was 12. Pectus excavatum was diagnosed. No surgical correction was undertaken; however, the owner was advised to simultaneously compress both sides of the thorax q12h. After 1 mo, radiographic examination showed that the heart was still displaced to the left, but there was no deviation of the caudal part of the sternum. The dog had frontosagittal and vertebral indices of 1.0 and 13.1, respectively (Figures 3c and 3d).

Figure 3.

Lateral and ventrodorsal radiographic views of case 2. Notice the heart displaced to the left (a) and the mild dorsal deviation of the caudal part of the sternum, beginning at the 6th sternebra (b). One month later, the heart was still displaced to the left (c), but no deviation of the caudal sternum was observed (d).

At the last evaluation, 2.4 y after treatment, the dog was clinically normal. Thoracic radiography revealed minimal displacement of the 7th sternebra and normal positioning of the heart (Figure 4). The frontosagittal and vertebral indices were 1.1 and 13.5, respectively. Results from a cardiac evaluation were normal, including those for arterial pressure, an ECG, and an echocardiogram.

Figure 4.

Lateral and ventrodorsal radiographic views of case 2, 2.4 y after conservative treatment. Observe the normal position of the heart (a), and the minimal displacement of 7th sternebra (b).

Discussion

Pectus anomaly is a deformity of the thoracic wall in which several ribs and the sternum grow abnormally, producing a convex (carinatum) or concave (excavatum) appearance to the ventral aspect of chest wall (1,2). Pectus excavatum has been reported in animals, most frequently in cats (3–11) and dogs (6,7,12,13), but it is considered to be an uncommon abnormality. The exact mechanism involved is unknown (1,4,7,14). Unbalanced overgrowth in the costochondral regions that push the sternum inward seems to be the most prevalent theory for its pathogenesis in humans (15,16). A postmortem dissection performed on a cat with pectus excavatum showed that the primary abnormality involved the ventral portion of the diaphragm (4).

No genetic defect has been found to be directly responsible for the development of pectus excavatum (2,14). However, familial occurrence of the pectus anomaly has been reported in humans (2,16,17) and in littermate dogs (7,12,13), as observed in the present cases. Among the littermates that have been reported, 3 were setter cross breed (12), 2 were pugs (7), and 2 were Welsh terriers (13). The present report is the 1st in schnauzer littermates. A pedigree study of 34 human families provided evidence of an inherited disorder, probably multi-factorial, although some families showed apparent Mendelian inheritance (17). In a retrospective study, 7 of 8 affected dogs were brachycephalic breeds; no predisposition was evident (7). In addition, an association between flat chest and pectus excavatum has been suggested in cats (18). Because of the potential for heritability, some authors have recommended that animals with pectus excavatum be neutered (5). The deformity is usually congenital (1,7).

Respiratory distress is the clinical sign most frequently observed by the owner (7), as occurred in both the cases reported herein, probably because the deformity becomes more pronounced during growth (4). Chest asymmetry is quite variable (5,16) and respiratory distress may be associated with displacement of the organs or restriction of ventilation (16). The deformity is generally in the caudal part of the sternum (1,7), but it has been reported in the cranial part in 2 dogs (13).

Vertebral deformities, cardiomegaly, and malposition of the heart may be detected (1,7,8,14) in association with pectus excavatum. In humans, pectus excavatum may occur as the only abnormality or in association with other syndromes, such as that of Marfan and Ehlers-Danlos (2,15,16). In the present cases, the initial heart displacement in the male dog was to the right, but in the female dog, it was to the left. In a retrospective study, the heart was displaced to the right in 2 dogs and to the left in 3 dogs and 4 cats (7). In another reported case in a cat, the cardiac silhouette was shifted into the right hemithorax (11).

In humans, heart murmurs and ECG abnormalities, such as right-axis deviation and depressed ST segments have been associated with displacement and rotation of the heart in pectus excavatum (15,16). No cardiac murmurs were detected in either case in this report, but ECG and echocardiographic abnormalities were found in case 1. Right-axis deviation was observed initially and remained even after the surgery. Elevation of the ST segment could have been secondary to the ventricle hypertrophy and the sinus tachycardia could have been associated with stress (19).

Mitral valve prolapse has been detected by echocardiography, especially in human patients with Marfan syndrome (16). A ventricular septal defect was reported in a dog with pectus excavatum (7). At last evaluation, an echocardiogram was normal in case 2, but in case 1, it still showed mild eccentric left ventricle hypertrophy. This echocardiographic finding may have been associated with the systemic hypertension (20) in dog 1, but its exact cause was not determined. Since the urine analysis showed low urinary density, the hypertension may have been associated with the beginning of renal disease. In addition, the low total protein and albumin concentration may have been related to liver, kidney, or intestinal diseases, among others. Further investigations should have been carried out, but the owner would not agree to this.

As reported by other authors, the frontosagittal and vertebral indices are important in defining the degree of the deformity (mild, moderate, or severe), as well as the response to the treatment (6,7,14). Based on suggested values for determining the severity of the pectus anomaly (7,14) as well as on the intensity of clinical signs, case 1 was characterized as moderate (reference ranges: frontal index: 2.0–3.0; vertebral index: 6.0–9.0) and case 2 as mild (reference ranges: frontal index: < 2.0; vertebral index: > 9), although the vertebral index for case 1 a 9.8 was above the reference range. Normal nonbrachycephalic dogs have a frontosagittal index of 0.8 to 1.4 and a vertebral index of 11.8 to 19.6 (7), as observed in both cases after treatment.

Some anesthetic precautions are necessary during the surgical procedure for treating pectus excavatum due to the age of the animal and the respiratory distress, such as avoiding an extended period of fast, maintaining body temperature, using anesthetic drugs that are easily metabolized, and using endotracheal intubation to provide airway access (1,14), as was done in the cases reported herein.

Corrective treatment using an external splint, as used in case 1, may alleviate the impaired ventilatory performance when done in young animals, since the costal cartilages and sternum are pliable (5,6,8). Possible complications with the method are damage to the internal thoracic vessels, heart, or lungs during the passage of the needle around the sternum (1); fatal reexpansion due to pulmonary edema (9); and postoperative skin abrasions, suture abscesses, and dermatitis (6). However, none of these was observed in the present case. A 14-day duration has been indicated for the splint to remain in place, since overcorrection of the sternum may occur from longer placement (14). The splint was maintained successfully for 21 d in case 1. A pin inserted longitudinally through the manubrium in association with an external splint (10), or a plate applied to the ventral side of the sternum (11) are alternative techniques that have been reported for use in young cats. In the case of older animals or those treated unsuccessfully with external splinting, surgical procedures, such as partial sternectomy (1) or ostectomy with external fixation (5), may be used.

Controversy remains as to whether the operative correction should be considered in all patients presenting with the pectus anomaly (1), since untreated pectus excavatum may be progressive (7) or have a spontaneous resolution (13,15), as observed in case 2. Probably the age of the animal, the clinical signs, and the severity of deformity are important factors in this decision. Since case 2, on presentation, had only occasional signs of respiratory distress after exercise, no clinical signs of heart dysfunction, and frontosagittal and vertebral indexes compatible with a mild deformity, the option was to perform conservative treatment, but maintain the follow-up. Although compression of the thorax by the owner was recommended, as suggested in another report (6), the benefit from this procedure is questionable and probably should be limited to cases without significant deformity of the sternum.