Clinical characteristics of horses and foals diagnosed with cleft palate in a referral population: 28 cases (1988–2011)

Abstract

The objective of this case series was to characterize the population, case presentations, and outcomes of 28 equids diagnosed with cleft palate over a 25-year period. The incidence of cleft palate was 0.04%. The median age at presentation was 2 mo (range: 1 d to 3 y). Fifty percent of the animals were < 2 mo old, 21% were ≥ 2 mo but < 1 y old, and 29% were 1 y of age or older. Males and females were nearly equally represented. Short-term outcomes included euthanasia in 50%, surgical repair in 11%, supportive care in 4%, and no treatment in 32% of cases; 46% of the animals survived to discharge. Defects involving both the hard and soft palate and/or aspiration pneumonia generally had less favorable outcomes. Though cleft palate is rare in horses, it should be considered as a differential diagnosis in horses of all ages with nasal discharge, a cough, a history of recurrent respiratory infections, poor growth, or chronic submandibular lymphadenopathy. Endoscopic evaluation of the pharynx may aid in earlier diagnosis and prognostication for owners.

Congenital defects affect between 1% and 4% of foals (1). Cleft palate, or palatoschisis, is an uncommon congenital defect affecting an estimated 0.1% to 0.2% of the equine population (1). In a study of 608 congenitally deformed foals and fetuses, cleft palate was the most common craniofacial defect and was identified in 4% of this population (2).

Cleft palate is well-described in humans and most domestic species, and has an estimated incidence rate of 0.6 per 1000 domestic animals, which is similar to that in humans (3). The human literature describes cleft palates as defects of the primary palate (the nares and lips) or the secondary palate (the hard and soft palate). In horses, cleft palate most commonly affects the caudal half to two-thirds of the soft palate (1). These secondary defects result from a failure of midline fusion of the lateral palatine processes. This fusion occurs in a rostral to caudal direction at approximately day 47 of gestation in the horse (1).

The causes of cleft palate are poorly understood. Suggested causes in domestic species include genetic factors, environmental, hormonal, and metabolic interactions, exposure to ionizing radiation or teratogens, vitamin and mineral deficiencies, and the administration of tranquilizers or corticosteroids during pregnancy (4). Cleft palates in cattle and swine are associated with the ingestion of toxic plants, including lupine species, wild parsnip, poison hemlock, and the wild tobacco tree (1,4,5). In cattle, cleft palates often present concurrently with arthrogryposis (5). Cleft palates in cattle may be caused by an autosomal recessive trait, bovine viral diarrhea virus or akabane virus infections, or selenium and manganese deficiencies (1,5).

The most common clinical sign associated with cleft palate is dysphagia with bilateral nasal discharge of milk immediately after nursing (1,6). It is also common for foals to show clinical signs of aspiration pneumonia, including coughing, abnormal lung sounds, tachypnea, tachycardia, and pyrexia (1,6). Large defects involving the hard palate may be diagnosed with a thorough oral examination, but definitive diagnosis is obtained via endoscopic evaluation of the nasopharynx (1,6,7).

Surgical repair is best suited for symmetrical defects that involve ≤ 20% of the soft palate. Reported methods of correction for palatoschisis include a transoral approach, laryngotomy, pharyngotomy, and mandibular symphysiotomy. Complications including dehiscence of the palatal suture line, oronasal fistula formation, mandibular osteomyelitis, instability of the mandibular symphysis, lower lip dehiscence, incisional infection, hypoglossal nerve damage and chronic dysphagia are reported to occur in up to 90% of attempted repairs (1,5–8,13). Failure of the repair is typically due to tension on the soft palate created by the lack of available tissue (5–7,13). Intensive post-operative care is required to address associated aspiration pneumonia and nutritional needs (4,6–11). Postoperative recommendations include parenteral feeding or enteral feeding through a nasogastric tube for 7 to 10 d to reduce irritation of the surgical site. Broad-spectrum antimicrobial therapy is continued for 5 d, but may be required for a longer time in animals with aspiration pneumonia (7). Due to the development of aspiration pneumonia in all but the most mildly affected cases, conservative management alone is rarely successful, and therefore, not recommended (1,6).

Although cleft palate is a well-recognized condition, the literature consists mainly of case reports and small case series with limited information regarding case presentations and outcomes in a population of both foals and adult horses (4,8–13). The purpose of this case series was to describe the presenting complaints, diagnostics, comorbidity, treatments, and outcomes of a diverse population of equids diagnosed with cleft palate.

Materials and methods

This study was performed as a case series. Electronic medical records at the Veterinary Medical Teaching Hospital at Texas A&M University from March 1988 to April 2013 were searched for horses diagnosed with cleft palate based on keywords “palatoschisis” or “cleft palate.” Criteria for inclusion included availability of the complete medical record and confirmation of the palatal defect via endoscopic evaluation, or direct visualization at surgery or necropsy. Twenty-eight cases were included, representing 0.04% of all equine medical and surgical admissions to this hospital. The following information was extracted from the records: signalment, presenting complaint, morphology of the defect, diagnostics performed, treatment, and outcome until discharge from the hospital. The proportion of Quarter Horses that were admitted to the hospital during the study period and the proportion of Quarter Horses that were diagnosed with cleft palate were compared for statistical significance.

Results

Case signalment

Twenty-seven horses and foals and 1 miniature donkey foal with cleft palates were presented to the Veterinary Medical Teaching Hospital over a 25-year period (1988 to 2013). Fourteen animals were male, 13 were female, and 1 was a castrated male. The median age at presentation was 2 mo (range: 1 d to 3 y). Fourteen (50%) of the patients diagnosed with cleft palate at this referral hospital were < 2 mo of age. Six patients (21%) were > 2 mo but < 1 y old. Eight patients (29%) were 1 y of age or older.

Quarter Horses were the most commonly represented breed. Thirteen Quarter Horses (46%) were diagnosed with cleft palate. The proportion of Quarter Horses diagnosed with cleft palate was not significantly different than the proportion of Quarter Horses admitted to the hospital during the study period (P = 0.81). Other cases included 6 Thoroughbreds (21%), 3 Arabians (11%), 2 mixed breed horses (7%), and 1 each of: American Paint horse, American miniature horse, Tennessee Walking horse, and miniature donkey.

History

The presenting complaints of equids diagnosed with cleft palate included dysphagia with nasal regurgitation, persistent nasal discharge, cough, aspiration pneumonia, submandibular lymphadenopathy, a history of pneumonia or respiratory infections, poor growth, wry nose, and colic. The most common presenting complaint was dysphagia with nasal regurgitation, seen in 17 horses (61%). Persistent nasal discharge, noted between feedings, was seen in 8 horses (29%). Six horses (21%) presented with a cough. Three adult horses (11%) had a history of pneumonia or recurrent respiratory infections. Two horses (7%) had suspected aspiration pneumonia prior to presentation. One (4%) 3-year-old horse presented with the sole complaint of a submandibular lymphadenopathy. One foal presented with wry nose, and another with colic. Fifteen (53.5%) horses had more than 1 presenting complaint. Cases with multiple presenting clinical complaints included: nasal regurgitation and aspiration pneumonia (n = 3), nasal regurgitation and cough (n = 2), nasal regurgitation, cough, and poor growth (n = 1), nasal discharge and a history of pneumonia (n = 1), nasal discharge and cough (n = 1), nasal discharge and poor growth (n = 1), nasal regurgitation and colic (n = 1), cough, multiple respiratory infections and respiratory noise (n = 1), submandibular lymphadenopathy and a history of pneumonia (n = 1), nasal discharge and a history of pneumonia (n = 1), a palpable palatal defect and wry nose (n = 1), or nasal discharge and a deviated nasal septum (n = 1).

Diagnostics and comorbidity

Diagnosis of cleft palate was made via endoscopic evaluation of the nasopharynx in 26 (93%) cases. Two cases of cleft palate involving the hard palate were diagnosed via palpation of the defect and were confirmed at surgery.

Complete blood (cell) counts (CBCs) were performed on 9 (32%) animals. Abnormalities on CBC included leukocytosis [20 300 cells/μL; reference interval (RI): 5400 to 14 300 cells/μL] in 1 foal, leukopenia (4900 cells/μL) in 1 foal, and hyperfibrinogenemia (14.7 to 26.5 μmol/L; RI: 2.9 to 11.8 μmol/L) in 4 foals. A normal leukogram was identified in 3 foals.

Lateral thoracic radiographs were obtained for 9 (32%) cases. All 9 animals had radiographic abnormalities, ranging from mild cranioventral lung changes consistent with aspiration pneumonia, to severe lung consolidation with air bronchograms in the ventral lung. One 2-year-old filly had a mild interstitial and bronchial pattern with dorsocaudal distribution.

Necropsies were performed on 9 animals (32%), in which 7 (25% of total cases) were confirmed to have pneumonia consistent with aspiration of feed material.

In total, 12 horses (43%) were diagnosed with aspiration pneumonia; 9 (75%) of these were diagnosed antemortem. Euthanasia was elected in 8 of the 12 (67%) horses with aspiration pneumonia and in 7 of 16 (44%) horses without aspiration pneumonia.

Defect morphology

Eighteen (64%) cleft palates were described as a midline soft palate defect (see Figure 1). Five cases (18%) had a midline soft and hard palate defect (Figure 2). All 5 cases were < 1 y of age. Two horses (7%) had an asymmetrical soft palate defect (Figure 3). Two horses (7%) had what was described as a bilateral soft palate abnormality or soft palate hypoplasia. One case (4%) was classified as an unspecified soft palate defect.

Figure 1.

Endoscopic image of the pharynx of a 3-year-old Quarter Horse mare with a midline soft palate defect.

Figure 2.

Transoral view of an extensive palatal defect involving both the hard and soft palate in a 2-day-old Quarter Horse filly. The nasal septum is indicated by the black arrow.

Figure 3.

Endoscopic image of the pharynx of a 3-year-old Arabian stallion with an asymmetrical cleft palate.

Short-term outcomes

Thirteen (46%) of the 28 animals were euthanized upon diagnosis of cleft palate. Three of 5 foals with hard palate involvement were euthanized.

Surgery was attempted in 4 cases (14%), all of which were < 2 mo of age. One foal was euthanized during surgery due to severe bilateral palate hypoplasia. In the remaining 3 foals, a mandibular symphysiotomy approach was used to repair the palatal defects. Two foals had both soft and hard palate defects. Dehiscence was noted after 8 d in 1 foal, while the other foal was lost to follow-up. The third foal had a soft palate defect and experienced a small degree of dehiscence at the cranial aspect of the palatal repair 12 d after surgery; this foal healed with no further interventions.

One foal (4%) was discharged following supportive care with antibiotics to address bronchopneumonia and 1 filly (4%) died of colitis while awaiting surgery.

Nine animals (32%) received no medical or surgical treatment and were discharged from the hospital. These cases had neither clinical evidence of active aspiration pneumonia nor any significant clinicopathologic abnormalities where blood was analyzed. Surgical options were discussed with all owners at the time of diagnosis but declined. All 9 of these cases had soft palate involvement only.

Discussion

The incidence of cleft palate in this referral population was 0.04% based on all equine medical and surgical admissions during the study time period. This is a similar incidence to that reported in a previous publication of cleft palate in domestic animals. Mulvihill et al (3) reported 331 cases with a cleft palate in a population of 684 650 domestic animals presenting to 14 veterinary school clinics in North America (0.05% incidence).

Males and females were nearly equally represented in this case series, with slightly higher incidence amongst males than females. A gender difference is reported in the human literature, in which isolated cleft palate has been reported more commonly in females (3). Mulvihill et al (3) reported a larger number of cleft palates in female horses and cattle, but this was not statistically significant. The number of cases with cleft palate in this referral population was limited and likely to be insufficient to demonstrate a clear gender bias.

Cleft palate is often assumed to be a lethal congenital defect; however, 13 animals (46%) in this series survived to discharge, 9 of which were discharged without intervention. This is similar to recent reports, with between 67% and 100% survival to discharge (12,13). Long-term outcomes were not available in most cases in this series based on the 25-year study period and transient nature of horse ownership. However, 1 Thoroughbred filly started race training and another continued to train. One stallion with an asymmetrical soft palate defect continued to breed mares.

The presenting complaints identified in these cases were numerous. The most common complaint was dysphagia with nasal regurgitation, but this was seen predominantly in foals < 2 mo of age. Persistent nasal discharge alone was the second most common chief complaint at presentation and was only seen in animals 2 mo of age or older. These complaints are well-described in the literature in association with cleft palate. However, the clinical signs in some cases were nonspecific, such as submandibular lymphadenopathy, intermittent cough, and poor growth. Considering cleft palate as a differential diagnosis in horses of all ages with any of the clinical signs discussed is essential to making accurate diagnoses.

Three animals 1 y of age or older had a history of respiratory infections as foals. Given the frequency of changes in horse ownership, the true incidence of foal pneumonia in this population may have been greater than described here. Foals with clinical signs of pneumonia, especially those with pulmonary consolidations identified with thoracic radiography or ultrasonography, are often diagnosed with Rhodococcus equi infection. Thorough history gathering and endoscopic evaluation of the nasopharynx would aid in earlier diagnosis of cleft palate. In this series, animals that were younger at the time of diagnosis generally had less favorable outcomes and more severe defects.

While cleft palate is often considered a differential diagnosis for nasal regurgitation of milk in foals, in this series 8 cases (29%) were 1 y of age or older and 14 (50%) were < 2 mo of age. A recent retrospective case series found that of 55 horses diagnosed with cleft palate, 16.4% presented as athletic horses, 1 y of age or older (mean: 5 y; range: 1 to 14 y) (13). The most common clinical sign in those cases was abnormal noise originating in the upper airway. The palatal defects in those horses were located at the caudal edge of the soft palate under the epiglottis, and it was suggested that this small cleft defect may not interfere with athletic function in these cases (13).

Foals < 2 mo of age were more likely to present with larger defects, especially involving those of the hard palate. Defects involving the hard palate were not diagnosed in any animal over 1 y of age. Nine of the 13 animals (69%) that were euthanized upon diagnosis were < 2 mo of age. Of these 9 animals, 7 had evidence of concurrent aspiration pneumonia or systemic illness and 1 was diagnosed with a concomitant deviated nasal septum. Euthanasia was elected following discussions of medical and surgical management. Decisions were based on poor prognosis or financial limitations. Conversely, horses diagnosed with cleft palate at > 1 y of age were more likely to be managed conservatively (75%) than horses < 1 year of age (15%). None of these conservatively managed cases had involvement of the hard palate, suggesting they had more modest palatal defects.

It is possible that horses diagnosed at a later stage in development are more likely to have compensated for the defect, as supported in a recent publication by Barakzai et al (12). The authors of this study described a population of 15 adult horses with previously undiagnosed cleft palate. The outcomes in these 15 cases were favorable; 2 horses had successful racing careers, many were lightly ridden, and the survival rate was 100%. Upper airway and tracheal contamination with masticated feed was common in the population of horses described by Barakzai et al (12), but was not associated with clinical signs of lung disease other than coughing. Couetil and Hawkins (6) also reported 3 horses diagnosed with cleft palate in adulthood with no clinical signs of aspiration pneumonia. In contrast, 3 of 8 (38%) horses > 1 y of age in our population were diagnosed with aspiration pneumonia based on physical examination findings and radiographic changes consistent with pneumonia. However, all 3 horses had mild changes and 2 were discharged without therapy.

Many case reports and case series of cleft palate in the horse mainly focus on cases undergoing surgical repair and subsequent outcomes (4,7,9–11). Given the preference for performing surgical repair prior to 6 wk of age, a case selection bias toward a younger population might exist in these studies (4,7,9–11). In a series of 11 cases of cleft palate that underwent surgical repair, 9 (82%) were < 1 y of age (8).

Surgery was attempted in only 4 cases in this equine population. Owners of horses diagnosed with cleft palate were informed of the likelihood of failure associated with surgical repair, which may have influenced their decisions regarding surgical intervention. In addition, many animals had only mild clinical signs and owners possibly chose not to pursue surgery based on potential risks and complications. The animals that underwent surgery in this population presented at 1 d, 13 d, 7 wk, and 1 y of age. Surgical repair was not possible in the yearling due to severe hypoplasia of the soft palate, and he was euthanized prior to anesthetic recovery. Survival to discharge following surgery was 100%. However, surgical repair failed 8 and 12 d after surgery in the 1-day and 7-week old foals, respectively. Unfortunately, both the 1-day and 13-day old foals that underwent surgical repair were lost to follow-up and long-term follow-up beyond 6 wk was not available for the 7-week-old foal that underwent surgery.

It is recommended that surgery be performed in foals < 6 wk of age in order to optimize visualization of the defect, minimize medical complications, and avoid airway contamination with solid food (1,7,9–11). Semevolos and Ducharme (11) report complete healing of the cleft palate defect in 50% of cases after 1 or more surgeries, but also report an 87.5% complication rate. Repeated surgeries were not performed on any equid in this case series. Other studies have a lower success rate, consistent with the findings of this case series, reporting palatal suture line dehiscence and subsequent oronasal fistula formation in up to 90% of surgical cleft palate repairs (1,4,5,7–11). In contrast, Murray et al (13) found that surgery was significantly associated with survival. In that study, 13 of 26 horses that did not have surgery were euthanized, compared with 3 of 26 horses that had surgery. However, despite this high survival rate, both complications and incomplete healing occurred in 65% of patients. The reasons for the reported variations in complication rates and survival following surgery are unknown, but may be attributed to the number of surgeries per horse, the surgical approach, differences between inclusion criteria amongst studies, and case selection. Further studies are needed to more accurately identify prognostic indicators and factors associated with successful repair of cleft palate. A recent case report described a laryngeal tie-forward procedure in a miniature pony diagnosed with cleft palate at 1 y of age (14). This procedure resulted in advancement of the larynx, such that the defect was covered by the epiglottis, and subsequent resolution of the pony’s dysphagia and respiratory infections. This surgical approach is commonly used for dorsal displacement of the soft palate and may warrant further consideration for the treatment of small, caudal, palatal defects in horses.

Cleft palate is rare in horses, but should be considered in horses of all ages with nasal discharge, cough, history of recurrent respiratory infections, poor growth or submandibular lymphadenopathy. Prognosis remains guarded for horses diagnosed with cleft palate, with or without attempted surgical repair. However animals with smaller defects appear to have less co-morbidity, a lower incidence of pneumonia, and a longer lifespan. In some cases, these animals may have careers as performance animals. CVJ