Feline megaesophagus associated with persistence of the right aortic archABSTRACT
Vascular ring anomalies are conditions that can be diagnosed in cats, although their frequency is lower than that in dogs. The fourth aortic arch is a condition characterized by the presence of a vascular ring that obstructs the physiological passage of food. The main complication is megaesophagus, with regurgitation often reported. The aim of this report is to describe the case of a cat with acquired megaesophagus due to the persistence of the right fourth aortic arch. A young cat with a history of constant regurgitation and weight loss was brought to a veterinary clinic. The patient had previously been evaluated at another veterinary clinic, but the presence of megaesophagus was not suspected based on simple radiography. In the new evaluation, megaesophagus was confirmed by thoracic radiography with a barium contrast esophagogram, with suspicion of vascular anomaly. The animal was admitted for veterinary hospitalization for intensive care and further echocardiographic evaluation to confirm the vascular anomaly. However, the cat developed aspiration pneumonia before the echocardiographic examination could be performed, and despite clinical intervention, it deteriorated and died. In the necropsy examination, persistence of the fourth aortic arch was confirmed, as well as cranial esophageal dilation proximal to the obstruction.
Keywords:
congenital disorder; cardiovascular; gastrointestinal alterations; vascular anomaly; vascular ring
RESUMO
Anomalias do anel vascular são condições que podem ser diagnosticadas em gatos, embora sua frequência seja menor que em cães. A persistência do quarto arco aórtico é uma condição caracterizada pela presença de um anel vascular que obstrui a passagem fisiológica do alimento. A principal complicação é o megaesôfago, sendo frequentemente relatada regurgitação. O objetivo deste relato é descrever o caso de um gato com megaesôfago adquirido devido à persistência do quarto arco aórtico direito. Um gato jovem, com histórico de regurgitação constante e perda de peso, foi levado a uma clínica veterinária. O paciente já havia sido avaliado em outra clínica veterinária, mas não houve suspeita da presença de megaesôfago com base na radiografia simples. Na nova avaliação, o megaesôfago foi confirmado por radiografia de tórax com esofagograma contrastado com bário, com suspeita de anomalia vascular. O animal foi internado para internação veterinária para tratamento intensivo e posterior avaliação ecocardiográfica para confirmação da anomalia vascular. No entanto, o gato desenvolveu pneumonia aspirativa antes que o exame ecocardiográfico pudesse ser realizado e, apesar da intervenção clínica, ele piorou e morreu. No exame de necropsia, a persistência do quarto arco aórtico foi confirmada, bem como dilatação esofágica craniana proximal à obstrução.
Palavras-chave:
distúrbio congênito; cardiovascular; alterações gastrointestinais; anomalia vascular; anel vascular
INTRODUCTION
Cardiovascular disorders and/or conditions are frequently observed in clinical practice and are often associated with rapid progression and a reduction in quality indicators and life expectancy. Various conditions of cardiovascular origin or those with cardiopulmonary repercussions present regional and/or systemic clinical manifestations, with symptomatic variability often associated with the underlying cause. Among primary cardiovascular disorders, congenital abnormalities are mentioned; these abnormalities are, by definition, associated with alterations at some stage in fetal development and therefore may involve genetic factors. Considering that congenital disorders are less commonly observed than persistent ductus arteriosus or valvular stenoses (Tremolada et al., 2012), the persistence of the right aortic arch deserves attention due to its pathogenesis and associated clinical manifestations.
The persistence of the right fourth aortic arch is a congenital anomaly characterized by the presence of the vascular ring, whereby the right embryonic arch gives rise to the functional aorta (Freitas et al., 2016). Thus, the obstruction of adjacent structures such as the esophagus and trachea can be observed variably. This vascular ring occurs due to the presence of the aortic arch on the right side, the pulmonary artery and the cardiac base in the ventral region, and the ligamentum arteriosum on the left (Birchard and Sherding, 1998). Thus, in the presence of the vascular ring, the esophagus becomes "trapped" between these structures. Consequently, this obstruction can cause gastrointestinal disorders, particularly in the esophagus, resulting in difficulty in food passage through the esophageal lumen and promoting megaesophagus (Tremolada et al., 2012). Megaesophagus is considered an esophageal dilation, either primary or secondary, due to factors interfering with the organs physiological function; therefore, cases of regurgitation and food retention are frequently observed (Chaplow, 2019).
Megaesophagus resulting from the persistence of the right aortic arch is acquired and originates due to abnormalities in the vascular ring, although it can also occur due to conditions associated with external compression, pyloric alterations, and the presence of foreign bodies (Chaplow, 2019). It is expected that affected animals will show signs of esophageal dilation cranial to compression, such that the anterior esophageal segment dilates due to food retention, while the posterior segment remains unaffected (Freitas et al., 2016). The objective of this report is to describe the case of acquired megaesophagus associated with the persistence of the right aortic arch in a four-month-old cat with a history of recurrent regurgitation.
CASUISTRY
A four-month-old, mixed-breed, male feline weighing less than one kilogram and not tested for feline immunodeficiency virus (FIV) or feline leukemia virus (FeLV), dewormed, unvaccinated, and fertile, was presented to a veterinary clinic in the metropolitan area of with a chief complaint of constant vomiting, as reported by the owners. The patient lived with another feline companion in an apartment and had no history of flea or tick exposure. During the initial evaluation, the owners reported that the patient was undergoing home care and experienced frequent vomiting, even after eating, although the patient accepted the use of soft treats. Additionally, they mentioned that they had initially administered ondansetron (1/2 tablet of 4 mg, PO; Agener União, São Paulo, Brazil) without veterinary prescription. The owners provided previous ultrasound, and radiographic examinations were performed nearly two months prior. The ultrasound examination did not reveal any noteworthy alterations, while the radiographic findings suggested mild bronchointerstitial pulmonary opacification with adequate expansion; a preserved tracheal course with a poorly defined lumen in the assessable portions; and no evident alterations in the mediastinum, pleural space, esophagus, or diaphragm. Radiographic analysis suggested that the pulmonary manifestations could be related to feline bronchial disease, necessitating the consideration of inflammatory and allergic etiologies.
During the new clinical assessment, vital signs were within normal limits, with a heart rate of 120 bpm, respiratory rate of 32 bpm, clear cardiopulmonary auscultation, normal moist mucous membranes, hydrated, a capillary refill time less than 2 seconds, lymph nodes with no alterations in volume, size, or consistency, and a rectal temperature of 38.5°C. No other notable organic system alterations were observed. Considering clinical history, hematological and serum biochemistry tests, which did not reveal any significant abnormalities, were suggested. Furthermore, a new radiographic examination with contrast agent was requested due to the initial suspicion of megaesophagus. Therefore, a positive contrast esophagogram with barium sulfate was performed in both the lateral and ventrodorsal projections of the cervical and thoracic regions.
The diagnostic impressions from the radiographic examination with positive contrast esophagogram revealed visible esophageal walls, notable dilation extending from the cervical to the thoracic region cranial to the cardiac base, containing heterogeneous material (food intake) in small quantity in the cervical region and a large quantity of gas; ventral displacement of the trachea and cardiac silhouette from their usual positions; usual lung field transparency without increased radiopacity; and contrast retention in the thoracic esophagus, with the contrast column extending cranially to the cardiac base (Fig. 1). The conclusive diagnosis was megaesophagus, with a recommendation for further evaluation through endoscopic and echocardiographic examinations.
Simple radiographic evaluation and after the use of barium sulfate as a contrasting substance. A and C - simple ventrodorsal and laterolateral projections (without contrast); B and D- ventrodorsal and laterolateral projections contrasted with barium sulfate (immediately after contrast administration). D - contrasted laterolateral projection, 20 minutes after contrast application. Note in images B, D and E, the presence of cranial esophageal dilation close to the heart base, suggestive of a vascular anomaly.
Given the patient's clinical condition, it was admitted for more specific care. Further evidence suggested that the patient had developed aspiration pneumonia, which was initially treated with amoxicillin-clavulanate (18mg/kg, q12h, PO; Agener União, São Paulo, Brazil), oxygen therapy, and dietary management. An echocardiographic examination was scheduled to be performed; however, before its execution, days after treatment initiation, the animal experienced cardiopulmonary arrest, decompensation, and died. The owners were informed of the situation and the benefits that necropsy would bring to the case closure, especially regarding the underlying cause. Necropsy confirmed the presence of cervical segment dilation prior to the structure causing compressive obstruction of the esophageal tract, with evidence of persistence of the right fourth aortic arch (Fig. 2). Thus, the conclusive diagnosis was determined to be acquired megaesophagus due to a congenital underlying cause involving the presence of the right fourth aortic arch.
Image of the tongue-esophagus-heart-lung segment showing esophageal dilation compatible with megaesophagus (yellow dashed line) (A). Presence of the 4th right aortic arch, with detail of the compressor ring (asterisk) that blocks the passage of the esophagus (yellow dashed line); note the presence of esophageal dilation cranial to the aortic arch (yellow dashed line) (B). Presence of the 4th right aortic arch (white arrow), with detail of the compressor ring (asterisk) that blocks the passage of the trachea (blue dashed line) and esophagus (yellow dashed line); note the presence of esophageal dilation cranial to the aortic arch (yellow dashed line) and the post-compression esophageal segment (green dashed line); the same can be seen in the post-compression tracheal region (dashed purple line) (C). Consider: H - heart, E - esophagus, T - tongue, L - lung, T - trachea.
DISCUSSION
Congenital anomalies are conditions associated with embryonic/fetal development that persist from birth to the first month of life (Ocarino et al., 2023). Vascular anomalies are less common in cats than in dogs, with frequencies of 0.6% (n=1/162) (Tidholm et al., 2015) and 85% (n=17/20) (Bascuñán et al., 2019), respectively. Bascuñán et al. (2019) reported that approximately 65% (n=13/20) of patients were diagnosed solely with right fourth aortic arch persistence, and 20% (n=4/20) had vascular ring anomalies with an aberrant left subclavian artery. In their study analyzing 20 patients with vascular ring anomalies, right fourth aortic arch persistence was the primary diagnosis. In the present report, the feline patient presented only the congenital defect in isolation, being the primary cause of the development of megaesophagus.
The embryogenesis process allows for the origin of six pairs of aortic arches, with the left side physiologically giving rise to the left subclavian artery, ligamentum arteriosum, and aorta and the right side to the right subclavian artery (Tremolada et al., 2012). Aortic arch persistence is classified as a congenital anomaly, particularly vascular, due to the presence of a ring formed by the aortic arch, ligamentum arteriosum, pulmonary artery, and cardiac base (Birchard & Sherding, 1998). Information regarding right fourth aortic arch persistence in cats is uncertain, according to Freitas et al. (2016), and is considered rare by Radlinsky (2014). In the present report, post necropsy examination revealed the presence of a vascular ring encompassing the esophagus and trachea near the cardiac base, consistent with the findings of Freitas et al. (2016).
Evidence suggests there is no breed predisposition; however, many cases of vascular ring disorders have been reported in various breeds, such as Siamese (Yarim et al., 1999), Maine Coon (Tremolada et al., 2012), and domestic shorthair, longhair and mixed-breed (Shannon et al., 2015; Freitas et al., 2016; Bascuñán et al., 2019; Silva et al., 2022; Duzanski et al., 2023; Raftery et al., 2023). The cat in the present case previously described was of mixed breed, consistent with reports by Freitas et al. (2016) and Silva et al. (2022). Vascular anomalies are more commonly observed in purebred animals, especially in dogs; data regarding this phenomenon in cats are lacking (Freitas et al., 2016). This may be due to the low number of reports of right fourth aortic arch persistence in felines, as observed in a study by Tidholm et al. (2015), in which the most observed congenital anomaly in cats was ventricular septal defect. The evidence described in a study suggests a possible relationship with DiGeorge syndrome, as similarities between the two conditions have been observed (Tremolada et al., 2012). DiGeorge human syndrome is characterized by the presence of deletions associated with chromosome 22, which may be associated with the development of congenital cardiovascular anomalies such as aortic arch persistence (McElhinney et al., 2001).
The occurrence of right fourth aortic arch persistence is mainly observed in young animals, with an average onset age of four months (Bascuñán et al., 2019). In addition, in Bascuñán et al. (2019) study, 75% (n=15/20) of the patients were diagnosed at less than one year of age, while only five were older. Several other reports indicate variability in age, although in all cases, the age factor is typically under two years. Freitas et al. (2016) described two cases in cats from the same litter, each two years old, which suggests a hereditary component. Additionally, other studies describe occurrences with nine months (Plesman et al., 2011), from two to eleven months (Tremolada et al., 2012; Mackus et al., 2024), under one year, and one and a half years (Monnet, 2017). Takeuchi et al. (2023) reported the case of a two-month-old female, Maine Coon, who’s left fourth aortic arch persisted. In the present report, the patient was diagnosed with the condition at four months of age, which partly agrees with the information described by Tremolada et al. (2012), Monnet (2017), and Bascuñán et al. (2019). The young age at diagnosis is estimated to be a congenital condition, along with associated clinical manifestations, which hinder solid food transport postweaning (Monnet, 2017). Occurrence in older animals may be associated with an effective liquid-to-solid food transition period, without signs of regurgitation and/or vomiting (Monnet, 2017). It is necessary that the causes of eating disorders such as megaesophagus have their underlying causes investigated. In the present report, the persistence of the fourth aortic arch as a cause of megaesophagus was only observed when clinical signs were present.
Regarding the information provided by the owners during the anamnesis stage, it is noted that they mainly complain of recurrent vomiting and/or regurgitation episodes, although they may also mention weight loss and lethargy in some cases. Notably, owners often use the term "vomiting" to refer to regurgitation episodes, although this does not strongly influence the diagnostic hypothesis (Bascuñán et al., 2019). In the report described by Freitas et al. (2016), the main complaint was episodes of regurgitation with poorly digested food and occasional diarrhea. Additionally, they noted an increase in volume localized in the cervical region, especially after feeding (Freitas et al., 2016). According to Monnet (2017), some animals only show clinical alterations due to right fourth aortic arch persistence when they lose weight and present frequent vomiting. Furthermore, they noted that for older animals, regurgitation due to right fourth aortic arch persistence is an uncommon suspicion. The same regurgitation presentation can also be seen in cats with left fourth aortic arch persistence (Takeuchi et al., 2023). In the present report, the main complaint from owners was the presence of constant regurgitation, consistent with the data described by Freitas et al. (2016), Monnet (2017), Bascuñán et al. (2019), and Takeuchi et al. (2023).
In the study by Bascuñán et al. (2019), regurgitation was present in 90% (n=18/20) and vomiting in 30% (n=6/20) of cats. Regarding regurgitation, 33% of the cats presented solid content after the event. Weight loss and growth difficulties were present in 15% (n=3/20) and 10% (n=10/20) of the patients, respectively (Bascuñán et al., 2019). Evidence of lethargy, coughing, dyspnea, bruxism, and hyporexia may also be observed. Clinical signs secondary to the established condition, such as aspiration pneumonia, may be observed in some cases (Takeuchi et al., 2023). It should be noted that aspiration pneumonia may not always occur (Plesman et al., 2011). In the present report, the animal also presented with aspiration pneumonia, a condition expected due to the underlying cause, consistent with the findings of Bascuñán et al. (2019) and Takeuchi et al. (2023).
According to Tremolada et al. (2012), the clinical manifestations of right fourth aortic arch persistence and vascular anomalies are often associated with esophageal obstruction. According to Bascuñán et al. (2019), the symptomatology associated with right fourth aortic arch persistence, in addition to obstruction, is also related to complementary regurgitation events. The presence of regurgitation is expected due to the pathophysiology of the condition; however, the occurrence of vomiting, although present, is infrequent due to the process of eliminating fluids that reflux through the obstructive vascular ring (Bascuñán et al., 2019). Laboratory alterations may not be observed in patients with right fourth aortic arch persistence, with values within the reference range (Freitas et al., 2016), as seen in the present report.
The diagnostic determination of right fourth aortic arch persistence in animals is based on the association of data provided during anamnesis with information from complementary examinations such as imaging studies or even necropsy findings. The diagnosis is based on the observation of clinical signs, evidence of cranial esophageal dilation and associated findings (Tremolada et al., 2012). In some cases, thoracotomies can be used for diagnosis (Tremolada et al., 2012). Contrast radiography with barium contrast is one of the most viable options for the diagnosis of megaesophagus, as described in studies such as Plesman et al. (2011) and Takeuchi et al. (2023). In the present study, contrast radiography with barium was chosen and performed as an auxiliary to the data provided by the anamnesis and clinical examination. Barium contrast esophagography allows visualization of cranial esophageal dilation near the cardiac base (Takeuchi et al., 2023). In the present report, the patient had previously undergone a simple radiographic evaluation, even with a history of recurrent vomiting. However, despite being in double projection, the radiographic evaluation did not show esophageal alterations. During the second evaluation, the request for thoracic radiography with barium contrast esophagography allowed visualization of cranial esophageal dilation at the cardiac base, with suspected congenital cause. These findings are consistent with those reported by Freitas et al. (2016), in which two cats underwent radiographic evaluation with barium sulfate, which allowed the identification of esophageal dilation and obstruction with a suspected diagnosis of vascular anomaly.
Multidetector computed tomography may be valid for evaluating vascular arch structure (Henjes et al., 2011). Furthermore, it can be used to investigate the presence of manifestations of aspiration pneumonia (Takeuchi et al., 2023). Tomography was not performed in the present report. In the present report, after the diagnostic determination of megaesophagus with possible vascular involvement, an echocardiographic examination for aortic evaluation was requested and scheduled, but the feline died before them. Angiography procedures (Plesman et al., 2011) and esophagoscopy (Bascuñán et al., 2019) can be performed, providing valuable information for the clinical condition. In some situations, the animal may die before diagnostic determination, making necropsy an essential examination. In the present report, the underlying cause of megaesophagus was not determined, only the secondary condition and its complications. Therefore, postmortem examination allowed the identification and visualization of the presence of vascular rings with esophageal and tracheal compression, as well as cranial esophageal dilation.
The treatment of right fourth aortic arch persistent patients often involves surgical intervention due to the clinical condition and consequences for patient survival, as well as complications from secondary disorders such as aspiration pneumonia. In the present report, the patient underwent intensive clinical treatment to control aspiration pneumonia with antibiotics, dietary modification, and oxygen therapy, but this treatment was unsuccessful. Therefore, for surgical procedures to occur, correct and detailed diagnostic steps are necessary (Takeuchi et al., 2023). The characteristics of the vascular ring anomaly formed are considered crucial variables for surgical execution and success (Takeuchi et al., 2023). Surgical procedures for correcting fourth aortic arch persistence have been described in some studies (Plesman et al., 2011; Freitas et al., 2016; Bascuñán et al., 2019). Thoracoscopic procedures involving ligation of the vascular ring can be successfully performed with minimal complications (Plesman et al., 2011). The major advantage of performing thoracoscopy is the observation of a larger surgical area; however, the authors emphasize that the size of the surgical region cannot be considered an impediment to not performing it (Plesman et al., 2011). Surgical procedures for vascular ring anomalies in cats are associated with postoperative complications, such as postoperative bleeding, leading to respiratory compromise and death (Plesman et al., 2011). In the present report, although the animal did not undergo surgery after death, surgical interventions are essential to improve the animal prognosis.
The prognosis for cats with right fourth aortic arch persistence depends on several factors, such as the age at diagnosis, associated complications, and the need for surgical intervention. The prognosis is considered reserved, with a significant risk of recurrence if appropriate procedures are not performed (Freitas et al., 2016). The presence of clinical signs and age at diagnosis may affect the prognosis, although there is no significant difference in survival between treated and nontreated animals (Tremolada et al., 2012; Bascuñán et al., 2019). The prognosis is considered favorable if surgical intervention is performed early, with a good response to treatment (Bascuñán et al., 2019; Mackus et al., 2024). Surgical treatment improved clinical signs and weight gain; however, it did not fully resolve the condition (Monnet, 2017). In the present report, the patient had a reserved prognosis due to the presence of aspiration pneumonia and worsening clinical conditions, which led to death.
CONCLUSIONS
In conclusion, the persistence of the aortic arch is a vascular embryonic/fetal anomaly that allows the existence of a vascular ring that restricts space and involves adjacent structures within this defect. Complications resulting from the presence of this condition can be observed, with one of the main complications being megaesophagus, characterized by dilation of the segment anterior to the ring, with food backlog and recurrent regurgitation. Affected animals have a poor prognosis because the content present in the esophageal lumen may aspirate into the respiratory system, often leading to aspiration pneumonia. In the present report, a feline patient under one year of age was diagnosed at a second appointment; however, due to the occurrence of aspiration pneumonia, she died. It is important to emphasize the importance of performing contrast radiographs through esophagography as a means of differential diagnosis for patients with constant regurgitation. Additionally, depending on the clinical course, postmortem examination allows for a better understanding of the underlying causes of secondary manifestations.
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