Incidental Tracheocele as an Unusual Presentation of Pneumomediastinum in the Trauma Setting

Abstract

Patient: Female, 25-year-old

Final Diagnosis: Tracheocele

Symptoms: Asymptomatic

Medication:—

Clinical Procedure: Computed tomography • flexible laryngoscopy/bronchoscopy

Specialty: Otolaryngology

Objective:

Rare disease

Background:

Tracheocele are rarely encountered air cysts formed due to tracheal wall outpouching through a weak vantage point. The majority are acquired in the adult population and are associated with conditions that weaken the tracheal wall. Most tracheoceles are diagnosed incidentally since many are asymptomatic or present with non-specific symptoms. Multidetector computed tomography (MDCT) scans are the most common imaging modality for diagnosis of silent tracheal cysts. Tracheocele have been very rarely documented in the trauma setting; therefore, in the setting of multiple body trauma diagnosis can be challenging.

Case Report:

We report a case of an acquired tracheocele after a high-impact blunt thoracic trauma with an admission diagnosis of suspected tracheal perforation. MDCT of the neck and chest demonstrated an irregularly multicystic-shaped air collection at the right posterolateral trachea upon evaluation. Flexible laryngoscopy and bronchos-copy results were unremarkable.

Conclusions:

Tracheocele are rare and asymptomatic pseudo-diverticulum of the tracheal wall. Many are diagnosed incidentally with imaging studies for other conditions. Nevertheless, in the trauma setting its diagnosis can be challenging and misleading. Consideration of conditions such as tracheocele is important to prevent any unwar-ranted treatment modalities.

Background

A tracheocele is a rarely encountered air cyst formed as a result of a tracheal wall outpouching through a weak point [1,2]. This diverticulum forms part of a broader group of cysts known as paratracheal cysts [3]. Histologic findings are consistent with air-filled cysts lined by pseudostratified epithelium [4].

Tracheocele can be further subdivided into 2 groups – congenital or acquired – based on etiology and a few other characteristic findings [1]. Although the etiology is unclear, most adult tracheocele are acquired. These are mostly associated with conditions that weaken the tracheal wall, such as obstructive lung disease, chronic cough, recurrent bronchitis, chronic smoking, or chest trauma. Nevertheless, Haddad et al suggested that multiple tracheal wall dilations (trachieactasis) can lead to further invagination of the mucosa. Hence, it is well known that an association exists between a weak tracheal wall and increased intraluminal pressure leading to a tracheal wall herniation [5–9].

Most tracheoceles are diagnosed incidentally since many are asymptomatic or present with nonspecific symptoms [2,3,10]; therefore, only about 30 cases have been reported in the literature worldwide. The exact prevalence is unknown but the incidence is approximately 2.4% or lower; making the condition rare [4,6,11–13]. Nevertheless, if symptomatic, these are mostly compressive in nature, leading to chronic cough, dysphonia, stridor, dysphagia, palpable neck mass, and, occasionally, vocal fold paralysis [4,7,10]. Multidetector computed topography (MDCT) scans are the most common imaging modality for diagnosing these silent tracheal cysts. However, bronchoscopy is the preferred modality for definitive diagnosis if a connection is observed. Many of these existing communications are not observed due to a narrow or fibrous tract between the tracheal wall and the cyst [2,14].

Tracheocele have been very rarely documented in the trauma setting. We report a case of an acquired tracheocele after a high-impact trauma, with a suspected tracheal perforation. In the context of a blunt thoracic trauma with pneumomediastinum, diagnosis of a tracheocele can be challenging [15]. This case report aims to raise awareness of tracheoceles within the multidisciplinary team evaluating and caring for trauma patients with pneumomediastinum.

Case Report

A 25-year-old female chronic smoker suffered a blunt thoracic trauma after being an unrestrained driver in a motor vehicle accident. The ambulance took her to a peripheral emergency department where computed tomography (CT) scans of the chest and abdomen were performed on the day of the event. She was discharged home from the emergency department but shortly thereafter was notified to return due to radiologic findings of a small air collection in the superior mediastinum. She was then subsequently transferred to our institution and the otolaryngology service was notified for evaluation due to the need to rule out any tracheal or esophageal injury approximately 24 h after the initial trauma.

MDCT of the neck and chest demonstrated an irregularly multicystic-shaped air collection at the right lateral posterior trachea, measuring 0.9×1.0×2.5 cm (Figure 1). The trauma surgery service performed an esophagram, which was unremarkable.

Figure 1.

3D CT imaging demonstrating irregularly shaped air collection at the right lateral posterior portion of the trachea containing internal septations (white arrow).

At the time of evaluation, the patient had no respiratory or swallowing problems. She denied shortness of breath, chest pain, hoarseness, dysphagia, or odynophagia. Upon performing the physical exam, no neck crepitation or neck masses were palpable and her voice was adequate. Hence, we proceeded to perform a flexible bronchoscopy after an uncomplicated transtracheal block with 4% topical lidocaine. Flexible laryngoscopy and bronchoscopy results were completely un-remarkable (Figure 2).

Figure 2.

Flexible tracheoscopy and bronchoscopy demonstrating intact tracheal walls.

The patient was treated conservatively since no consequences from the trauma had developed. She was discharged home several days after admission in good health and was given a follow-up appointment in our clinics. No surgical management was planned due to the asymptomatic nature of the condition.

The patient was evaluated as an outpatient in our clinics to ensure she remained clinically asymptomatic after recovery. She was examined about a month after the initial trauma and, upon evaluation, was still asymptomatic. A follow-up flexible laryngoscopy and bronchoscopy were performed and were, once again, unremarkable. No follow-up radiologic imaging was performed.

Discussion

Tracheocele are rare cystic outpouchings of the inner lining of the trachea that may be congenital or acquired in nature. Miller et al described that such outpouchings may occur at weakened points of amuscular regions between bands of trachealis muscle that unite the cornua of tracheal rings [4,10,16,17]. Most of these go undiagnosed due to its asymptomatic presentation. Nevertheless, the literature has described this pathologic abnormality due to its rate of incidental findings on imaging studies. The distinction of these as acquired versus congenital is difficult.

Congenital tracheocele are mostly due to an existing defect in the sixth week of fetal life while the upper respiratory system is being developed [2]. It can be due to either a defect in the endodermal differentiation during the development of the membranous posterior tracheal wall or from a defect in the development of the tracheal cartilage [6,18]. Most congenital tracheocele, considered true diverticula, consist of a small single cystic protrusion containing all 3 layers of trachea filled with mucosal contents and located at 4 to 5 cm from the vocal cord or 1 cm above carina [2,5,16,18,19–22].

As in our patient, most tracheocele in adult patients are acquired. The precise etiology of these is still unknown but a clear association exists with conditions that weaken the tracheal lumen such as prolonged inflammatory upper airway conditions, sudden increased intraluminal pressure, COPD, chronic cough, and tracheal mucus impaction [4,16,18,19,21]. The increased intraluminal pressure that our patient experienced, caused by the impact force, may have led to an outpouching located at the most susceptible site, the right posterolateral trachea. It is suggested that this is the most vulnerable site due to a lack of positional support by the esophagus, in contrast to the left side [1,4,15,19,21]. Acquired tracheocele are multicystic, and consist only of respiratory epithelium and thus are considered pseudodiverticula [1,2]. These can be located at any tracheal level between the extrathoracic and intrathoracic trachea [17,19].

Two diagnostic modalities exist to identify tracheocele. MDCT is usually the imaging study that characterizes the tracheocele as an incidental finding given most are asymptomatic [1]. Even when a connection exists, this is usually not observed. Buterbaugh evaluated 702 cervical spine CT scans in post-traumatic patients and demonstrated a connection in only 35% of the patients with paratracheal air cysts [23]. The ideal procedure to identify a connection is either a flexible or rigid bronchoscopy. However, bronchoscopy has low sensitivity since a connection is not always identified [1]. Hence, inability to identify the tract, such as in our patient, does not exclude the diagnosis of a tracheocele.

In any trauma center, the presence of pneumomediastinum after a high-speed motor vehicle collision causing a blunt thoracic trauma raises suspicion of tracheal or esophageal perfo-ration, making diagnosis of tracheocele difficult. The presence of a paratracheal air collection can be misinterpreted and lead to unwarranted surgical treatment. For this reason, the aim of our case report was to help document and raise awareness among the multidisciplinary team caring for trauma patients.

There is very limited documentation of tracheocele diagnosis in the setting of traumatic injuries, but Naritmasu et al and Clemente et al described similar events in which high-impact blunt thoracic injuries due to a motor vehicle accident and a fall, respectively, led to the diagnosis [9,15]. Similar to these 2 cases, no evidence of traumatic injury within the tracheal lumen on bronchoscopic evaluation was observed in our case. These findings led to the determination that these tracheal diverticula may have been incidental findings and not necessarily a direct result of the trauma. However, traumatic injuries to tracheal mucosa are not always easily identifiable on bronchoscopy [15]. Buterbaugh et al conducted a large retrospective study of imaging in trauma patients to identify the prevalence of paratracheal air cysts that may be misidentified as free air within the mediastinum. Similar to our case, they hypothesized that increased intratracheal pressures generated during traumatic injury could lead to an acquired tracheocele [22]. They found no association between the prevalence of right-sided tracheocele and trauma. However, this does not exclude the possibility that trauma may be a possible etiology for acquired tracheocele. Moreover, the study recognized the potential for misdiagnosis of pneumomediastinum in cases of paratracheal air cysts in patients with traumatic injuries. Tracheocele should always be considered in the differential diagnosis of all patients with pneumomediastinum in the setting of traumatic injury.

Conclusions

Tracheocele are rare and asymptomatic pseudodiverticulum of the tracheal wall. Many are diagnosed incidentally with imaging studies aimed to evaluate other conditions. Nevertheless, in the trauma setting its diagnosis can be challenging and misleading and it is important to rule out any associated traumatic complications. However, consideration of conditions such as tracheocele should be part of the differential diagnosis for pneumomediastinum to prevent any unwarranted treatment modalities.