Tracheobronchopathia osteochondroplastica associated with skin cancer: a case report and review of the literature

Discussion

Tracheobronchopathia osteochondroplastica (TO) is a rare benign disorder characterized by numerous osseous and cartilaginous submucosal nodules projecting into the lumen of the trachea and bronchi. TO was originally described by Wilks in 1857. At autopsy, he found the larynx, trachea and bronchi to be covered by a number of bony plates [3].

Since then, around 300 cases have been reported in literature [1]. Most cases had been an incidental finding at autopsy, but an increasing number of cases were diagnosed during bronchoscopic examination [5] or chest computed tomography (CT) scanning [6]. TO is detected in approximately one of every 2000 bronchoscopies [7].

The nodules originate in the airway cartilages and thus typically spare the posterior membranous wall of the airways.

The disease is usually identified in adults older than 50 years, but it has also been described in children. There is no sex predominance and no clear link with smoking [8].

Clinically, TO is usually asymptomatic and incidentally discovered, but can present with wheezing, cough, hemoptysis, dyspnea, and rarely obstructive symptoms [9]. Few cases of TO are diagnosed after difficult intubation [8, 10]. Currently, diagnosis is made during bronchoscopy, however imaging studies, most frequently CT or magnetic resonance imaging, can identify TO [11]. Chest radiography is usually normal.

CT can reveal multiple nodular submucosal irregularities, some of which calcified, with sparing of the posterior tracheal wall. It is also important in detecting the complications such as lobar collapse and post obstructive bronchiectasis [12]. Detection and diagnosis of TO by a CT scan require careful interpretation of the findings with extensive knowledge of the disorder.

In our case, the chest radiography was normal, but the CT scan demonstrated multiple nodular densities in the trachea.

If CT scanning may be suggestive, final verification requires bronchoscopy with biopsy.

Endoscopic features are typical and pathognomonic. TO appears as whitish, hard spicules projecting into the tracheal lumen from the anterior and lateral walls, with sparing of the posterior wall. Also the larynx and the main bronchi could be involved [8]. The spiculs are firm and frequently difficult to biopsy through the fiberoptic bronchoscope. In our case, bronchoscopic findings were characteristic of TO.

Histological examination of the nodules is non-specific, it usually reveals varying combinations of cartilaginous, osseous and haemopoietic tissue within a calcified protein matrix, protruding into the bronchial lumen. The overlying mucosa is often the site of squamous metaplasia [12].

Lesions do not carry any malignant transformation potential. They progress slowly and rarely need treatment. In a long time period, obstruction and recurrent infections might occur [4].

There is no definitive therapy: treatment is only symptomatic, which includes antibiotics in case of bacterial infections, mechanical measures to remove obstructing nodules using either cryotherapy, laser excision, external beam irradiation, radiotherapy, stent insertion or surgical resection therapy [13–15].

The differential diagnosis to the bronchoscopic picture of multiple nodules includes TO, amyloidosis, endobronchial sarcoidosis, calcific tuberculosis, papillomatosis and tracheobronchial calcinosis [1].

The etiology of TO remains obscure. Hypotheses include acquired connective tissue metaplasia, cartilaginous ring exotoses, ossification of elastic cartilage, and reactive inflammation secondary to chronic infection. The potential for genetic predisposition has also been considered, given the rare occurrence of familial cases [7].

A few cases have been associated with lung cancer [16, 17], and a few with thyroid tumor or thymoma [18, 19].

In the Japanese literature, approximately 140 cases have been published since the first one reported by Kidokoro in 1938 [20].

Yokoyama [21], referring to japanese literature, reported that malignant tumors were associated among 19% of the patients with TO. He also reported that lung cancer was found in 11.1% of patients with this disease, and the most frequent histologic type among the concomitant lung cancer is adenocarcinoma. However, these findings are inconsistent and the association may be coincidental [1].

Our patient was diagnosed as TO and skin cancer. To our knowledge, skin cancer has never previously been reported in association with TO.

In our case, we didn’t consider TO initially given its rarity and the context of malignancy. The histological findings confirmed the diagnosis.

If TO is not suspected in the differential diagnosis of malignant invasion of the trachea, it can easily be misdiagnosed especially in the patients complicated with malignancy at the same time.

Therefore, in cases of TO complicated with cancer, careful examination is necessary, including bronchoscopy and biopsy of tracheal lesions.