Primary Tracheal Leiomyoma in a Dog: A Case Report

1. Introduction

The incidence of primary tracheal neoplasms in dogs and cats has not been described, but it is considered to be very low, as in human medicine, where an incidence of 0.142–0.27 cases per 100,000 people has been reported [1,2]. The neoplasms described include adenocarcinoma, carcinoma, extramedullary plasmacytoma, leiomyoma, fibrosarcoma, mast cell tumor, rhabdomyosarcoma, and squamous cell carcinoma [3,4,5,6,7,8]. However, most reported tracheal tumors are malignant [9,10].

Regardless of the type of neoplasm, whether benign or malignant, the clinical signs and radiographic findings are usually similar. These tumors tend to cause airway obstruction [11], resulting in nonspecific clinical signs, including coughing, respiratory difficulty, blood-tinged sputum, bronchitis, and aphonia [12,13]. Radiographically, they usually appear as single, well-defined intratracheal masses [5].

They are usually associated with middle-aged to older patients, although benign osteochondroma and osteochondral dysplasia have been described in dogs up to 2 years of age [14,15].

Although only isolated cases have been reported in both human and veterinary medicine, in human medicine tracheal leiomyoma is known to be more common in men [16].

Given the potential for tracheal masses to cause severe, potentially life-threatening airway obstruction requiring prompt intervention, computed tomography (CT) and bronchoscopy are valuable complementary diagnostic modalities for accurately characterizing lesion location and extent, assessing luminal and extraluminal involvement, obtaining tissue samples, guiding surgical planning, and supporting prognostic assessment [14,17,18]. Depending on the tumor base, alternative approaches such as endoscopic resection using a polypectomy snare or laser therapy may be considered [19]. Tracheal resection and anastomosis may provide a longer disease-free interval than endoscopic debulking, even when complete surgical margins are not achieved [20].

2. Case Description

2.1. Clinical Presentation

A 12-year-old, 27 kg, spayed female Pitbull was presented with a history of chronic respiratory signs, including coughing, sneezing, cyanosis, and tachypnea, characterized by seasonal worsening during the winter months and progressive deterioration over the preceding month. The dog was admitted as an emergency because of signs compatible with severe upper airway obstruction, including inspiratory dyspnea, tachypnea, and cyanotic episodes. Examination of the upper airway revealed bilateral laryngeal paralysis (LP), and left arytenoid lateralization was performed. Despite surgical treatment, and although hematological and biochemical analyses were within the reference intervals, including serum total thyroxine concentration, the dog continued to show signs of respiratory obstruction requiring orotracheal intubation. Emergency bronchoscopy was subsequently performed and revealed an intraluminal tracheal mass causing partial airway obstruction. Because of the obstructive compromise and the need to secure the airway, a temporary tracheostomy was performed caudal to the mass.

2.2. Imaging Diagnosis

Computed tomography was performed for surgical planning of tumor resection and to assess the presence of additional masses or metastatic disease. CT revealed a tracheal mass extending from the 9th to the 15th tracheal ring and occupying almost 100% of the tracheal lumen. The mass showed a mean attenuation of 33 HU, consistent with a soft-tissue lesion. Persistent airway obstruction was observed despite adequate glottic opening following the previous left arytenoid lateralization. The mass appeared to arise from the dorsal tracheal ligament and caused esophageal compression at the level of the C3–C4 vertebral bodies (Figure 1). No evidence of metastatic disease was detected.

Thoracic and cervical radiographs did not reveal radiographic findings suggestive of an intraluminal tracheal space-occupying lesion or overt tracheal neoplasia.

2.3. Surgical and Anesthetic Management

The patient was positioned in dorsal recumbency with the neck extended. A ventral midline skin incision was made from the caudal border of the cricoid cartilage and extended 12 cm caudally, including the temporary tracheostomy site. The sternothyroid muscles were separated along the midline raphe, and the trachea was exposed. The mass was located on the right dorsolateral aspect of the trachea and extended into the tracheal lumen. The carotid sheath and recurrent laryngeal nerve were dissected bilaterally. The trachea was transected 20 mm caudal to the cricoid cartilage and one tracheal ring caudal to the tracheostomy site. In total, 10 tracheal rings were removed, corresponding to 24% of the total tracheal length. Cranial and caudal surgical margins of 10 mm were obtained (Figure 2).

Stay sutures were placed using 2-0 nylon and were tied after completion of the anastomosis to provide additional support. The anastomosis was initiated by placing three 2-0 nylon sutures in the dorsal tracheal ligament. The remaining sutures were placed circumferentially, engaging one proximal and one distal tracheal ring. All sutures were preplaced and tied at the end of the anastomosis (Figure 3).

Anesthetic maintenance was initially achieved using total intravenous anesthesia with propofol, with intubation performed through the tracheostomy. Once the end-to-end tracheal anastomosis was initiated, orotracheal intubation was performed, and anesthesia was changed to partial intravenous anesthesia with isoflurane. As part of anesthetic maintenance, a continuous rate infusion of dexmedetomidine was also administered, together with 100% oxygen.

2.4. Histological Findings

The surgical specimen consisted of a tracheal segment including 10 tracheal rings and a well-demarcated, firm, fleshy mass measuring 3 cm in diameter. The mass compressed the trachea and caused marked narrowing of the tracheal lumen (Figure 2c).

Histopathological examination showed that the neoplasm originated from the tracheal muscle. It was non-invasive, non-encapsulated and well demarcated. The neoplastic cells were arranged in dense bundles separated by scant connective tissue and had indistinct cytoplasmic borders. The nuclei showed the characteristic cigar-shaped morphology, being elongated with rounded ends. No mitotic figures were observed in the examined sections. The final diagnosis was tracheal leiomyoma (Figure 4).

2.5. Outcome

The patient recovered without complications. Postoperative management included fluid therapy with lactated Ringer’s solution at maintenance rate, together with multimodal analgesia consisting of methadone (0.1 mg/kg every 4 hours) combined with metamizole (10 mg/kg every 12 h). Analgesia was progressively tapered according to pain assessment using the Glasgow Composite Measure Pain Scale.

Amoxicillin-clavulanic acid (20 mg/kg every 12 h) was administered as perioperative antimicrobial prophylaxis. Additional intravenous treatment included maropitant as an antiemetic (1 mg/kg every 24 h) and dexamethasone as a steroidal anti-inflammatory drug (0.1 mg/kg every 24 h).

The surgical site was kept clean and dry throughout the hospitalization period. The patient was discharged 48 hours after surgery with no respiratory signs. At the 15-day follow-up examination, the patient showed no respiratory abnormalities, except for occasional mild coughing episodes when excited or nervous. Continued follow-up was performed by telephone, during which the owners reported a favorable clinical outcome. Currently, 2 years after end-to-end tracheal anastomosis, the patient remains free of respiratory signs. The owners report that she is more active than ever, running and playing without respiratory distress or coughing.

3. Discussion

Primary tracheal neoplasms are uncommon in both veterinary and human medicine [21,22]. Tracheal leiomyoma accounts for approximately 1% of all reported tracheal neoplasms, and more than 90% of reported tracheal tumors are malignant [16,23,24]. In dogs, tracheal neoplasms can be classified as cartilaginous or non-cartilaginous, with the latter being more frequent; tracheal leiomyoma is included within this group [25].

Consistent with previous reports, in which tracheal neoplasms are most commonly located in the cervical portion of the trachea and usually occur in middle-aged to geriatric patients [13], the patient in the present case was diagnosed at 11 years of age, and the lesion was located at the level of the C3–C4 vertebral bodies.

The available literature on tracheal leiomyomas is scarce. In human medicine, primary tracheal leiomyomas appear to occur more frequently in men, whereas pulmonary parenchymal leiomyomas have been reported more commonly in women. In this context, leiomyomatous lesions of the respiratory tract should be differentiated from benign metastasizing leiomyoma, a rare entity described mainly in women with a history of uterine leiomyoma or previous uterine surgery. Therefore, assessment of reproductive and surgical history is relevant [26]. In the present case, the patient was a spayed female with no known history of uterine leiomyoma. In addition, CT was performed to rule out the presence of other masses, and no additional lesions or evidence of metastatic disease were identified. These findings, together with the solitary nature of the lesion, supported a primary tracheal origin of the neoplasm.

The main risk associated with this type of neoplasm does not necessarily lie in malignant biological behavior, but rather in its ability to cause functional airway obstruction, which may severely compromise ventilation [11,26]. In this case, the clinical signs progressed gradually, with acute worsening that required temporary tracheostomy to stabilize the patient and allow planning of definitive oncological surgery.

The clinical signs were nonspecific, as previously reported, and included respiratory abnormalities compatible with upper airway obstruction, such as inspiratory dyspnea, tachypnea, cyanotic episodes, and hoarseness [13,26,27]. Although esophageal compression was observed on CT, the dog did not show dysphagia. On unenhanced CT, the mass showed a mean attenuation of 33 Hounsfield units (HU), consistent with soft-tissue attenuation. This value falls within the range reported for human tracheobronchial leiomyomas (25–46 HU), which typically demonstrate homogeneous enhancement following contrast administration [28].

Although intraluminal tracheal masses may be radiographically identified as well-defined lesions [5], in this case, thoracic and cervical radiographs did not reveal findings compatible with tracheal neoplasia. The endotracheal mass was not diagnosed until emergency bronchoscopy was performed because of worsening respiratory signs after left arytenoid lateralization. This finding highlights the importance of considering intraluminal tracheal lesions in patients with persistent obstructive signs, even when radiographic examination does not show evident abnormalities.

From an anatomical and surgical perspective, the trachea is part of the lower respiratory tract and, in mammals, consists of a sequence of C-shaped hyaline cartilage rings connected by annular ligaments and joined dorsally by the trachealis muscle [29]. In dogs, the trachea comprises approximately 35–46 tracheal rings (cartilagines tracheales) [30]. Although there is no definitive consensus regarding the maximum length of the trachea that can be safely resected in dogs, some studies suggest that up to 50% of the adult tracheal length may be removed [31]. However, resection of approximately 30% of the tracheal length has been reported to be associated with cranial displacement of the lungs [32]. In human medicine, resections exceeding 50% of the tracheal length usually require reconstructive techniques other than end-to-end anastomosis because of the tension generated at the suture line [33]. Conversely, studies in sheep have shown that up to 58% of the trachea can be resected without the development of complications [34].

The surgical technique used in this case was segmental tracheal resection with end-to-end anastomosis, as previously described in the veterinary surgical literature [35]. In the present patient, the resection represented 24% of the total tracheal length. A more extensive resection was not required, as adequate macroscopic surgical margins of 10 mm were obtained both cranially and caudally. This percentage is within the limits considered safe in the literature, which probably contributed to reducing the risk of complications associated with anastomotic tension [36].

Regarding surgical margins, specific evidence for canine tracheal tumors is limited. However, in some malignant tracheal neoplasms, such as squamous cell carcinoma, margins greater than 5 mm have been described as sufficient [20]. In this case, because the tumor was a leiomyoma and complete resection was achieved, the prognosis was considered favorable [37]. This was supported by the clinical outcome, as the dog remained free of respiratory signs and showed no evidence of recurrence during a two-year follow-up period. Owing to the broad base of attachment and the extent of the lesion, endoscopic excision by bronchoscopy was not considered appropriate.

Although the surgical technique of tracheal resection and anastomosis is well described in veterinary medicine, the available information on anesthetic management during these procedures remains limited [38,39,40]. In the present case, the patient did not require retrograde intubation or the use of a supraglottic airway device. Initially, ventilation was performed through the previously placed temporary tracheostomy, which allowed safe airway control during the initial phase of the procedure. Once the end-to-end anastomosis had been initiated, the patient was intubated orotracheally, allowing completion of the tracheal reconstruction without significant interference with the surgical field.

In human medicine, although mortality associated with tracheal resection and reconstruction in specialized centers is low, approximately 1-2%, the complication rate may reach 18.2% [41]. In the present case, after tracheal resection and end-to-end anastomosis, the patient did not develop postoperative complications. Placement of a cervical guardian suture to limit neck extension and reduce tension on the anastomosis was not required. Likewise, no relevant anesthetic complications, such as episodes of hypoxemia, which have previously been described in some reports of anesthetic management of tracheal surgery in small animals, were observed [38]. Regarding LP, the most commonly reported cause is idiopathic, although acquired causes such as bite trauma or mediastinal masses have also been described [42]. Less frequent causes include mineralization of the surrounding muscles [43] and muscular pseudotumors [44]. In the present case, LP was suspected to be secondary to involvement of the recurrent laryngeal nerve by adhesion of the tracheal tumor, although a definitive causal relationship could not be confirmed.

Overall, this case highlights the importance of including intraluminal tracheal neoplasms in the differential diagnosis of patients with persistent obstructive airway signs, even when radiographic findings are nonspecific. Bronchoscopy and CT were essential for diagnosis and surgical planning. Segmental tracheal resection with end-to-end anastomosis allowed complete excision of the lesion, with a favorable clinical outcome and no relevant perioperative complications.

5. Conclusions

Tracheal leiomyomas are rare neoplasms in both veterinary and human medicine. Although they may cause marked respiratory signs due to functional airway obstruction, complete surgical resection of the mass can be curative. However, the management of these lesions requires close coordination between the surgical and anesthetic teams, particularly to ensure adequate airway control throughout the procedure.

The patient is currently 13 years old, and 2 years have elapsed since surgery. During this period, no recurrence of respiratory signs has been observed. The owners report only a mild change in the tone of the bark, similar to that noted at the onset of the clinical process.

This case highlights the importance of a multidisciplinary approach in rare or complex conditions, such as tracheal leiomyoma, and demonstrates that appropriate diagnostic, surgical, and anesthetic planning can lead to favorable long-term clinical outcomes.