Atypical bronchial carcinoid with postobstructive mycobacterial infection: case report and review of literature

Pulmonary carcinoids are NET arising from Kultchitzsky cells and 25% occur in the respiratory tract [1]. Pulmonary carcinoids represent about 1–2% of all primary lung tumors with an age-adjusted incidence rate ranging from 0.2 to 2/100000 population/year in both US and European countries [2].

Carcinoid tumors are divided into low-grade (typical) and intermediate-grade (atypical), based on mitotic activity and presence of necrosis. The location of pulmonary carcinoids can be central or peripheral, although the majority is located centrally [2, 3]. Respiratory symptoms are generally present only in central lesions, while peripheral forms are generally discovered as an incidental finding. The most frequent respiratory symptoms are recurrent chest infections, cough, hemoptysis, chest pain, dyspnea, and wheezing.

The cause of pulmonary carcinoid is unknown and there is no strong association with smoking or environmental carcinogens [1, 2].

A 45-year-old female, never smoker and without comorbidity, presented with cough, low grade fever and mild weight loss. There was no haemoptysis. She had no contact with tuberculosis patients but she had travelled to endemic countries in Asia and Africa. There was no history of recurrent infections in the past. She was diagnosed with pneumonia and treated with various courses of antibiotics but without resolution of symptoms. Physical examination revealed decreased breath sounds in the left upper lobe. Chest X-ray revealed a consolidation in the upper left hilum and left upper lobe (Fig. 1). CT scan showed a central nodular intraluminal lesion with bronchial thickening and postobstructive pneumonia in the left upper lobe. No other endobronchial lesions or focal intrapulmonary pathology was found. There was no lymphadenopathy and no pericardial or pleural effusion (Fig. 2 a, b). Bronchoscopy showed a well-defined endobronchial tumor in the apicoposterior segment of the left upper lobe. The patient was subsequently referred to our hospital for endobronchial treatment. Rigid bronchoscopy with electrocautery was attempted, but unsuccessful due to the difficult location of the lesion (Fig. 3). Subsequent left upper lobe lobectomy was uncomplicated and resulted in a radical resection, pT1bN0R0. The resected lobe showed a perihilar mass with dilation of distal bronchi that were filled with mucinous material. The peripheral lung parenchyma contained multiple ill-defined, white to yellow consolidations (Fig. 4a, b). Histology and mitotic count was consistent with atypical carcinoid (Fig. 5a, b, c, d). In the peripheral lung parenchyma, granulomatous inflammation was found (Fig. 6a). Ziehl-Neelsen staining demonstrated unequivocal acid fast bacilli (Fig. 6b). PCR for Mycobacterium genus and Mycobacterium tuberculosis (MTB) complex performed on the resection specimen were negative. Three cultures from the surgical specimen were negative for the MTB and NTM. Because tuberculosis could not be ruled out, we advised the referring hospital to start treatment with antituberculous drugs. However, at the referring hospital it was decided not to treat because of the negative PCR and culture. Since then (now 14 months of follow-up) the patient has been well, without signs of infection. CT scan of the chest during follow-up showed no signs of active tuberculosis or recurrence of the carcinoid.

Pulmonary carcinoids are classified according to the WHO 2015 classification as typical or atypical [4]. Typical carcinoid tumors are more common and found more centrally within the major bronchi, whereas atypical carcinoid tumors tend to arise in the periphery [5]. Bronchial carcinoid tumors are not related to smoking and they may develop more often in patients with a previous history of malignancy of the skin, urogenital tract and respiratory tract [1, 2].

Patients with typical carcinoid have a favorable prognosis with a 10-year survival of up to 80–90%, compared to 40–60% in patients with atypical carcinoids [2].

The most frequent symptoms in patients with bronchial carcinoids are cough, dyspnea and hemoptysis. Lobar obstruction often occurs in bronchial carcinoids and causes postobstructive pneumonia [6, 7]. The diagnosis is often delayed, and patients may have received several courses of antibiotics to treat recurrent pneumonia before the pulmonary carcinoid tumor is diagnosed. Endocrine manifestations occur in 1–7% of cases in addition to carcinoid syndrome [2]. The gold standard of imaging is a contrast CT scan. A chest X-ray usually reveals parenchymal changes due to obstruction [1]. Bronchoscopy is a very important tool in diagnosing bronchial carcinoid tumors. Surgical resection is the mainstay of treatment [1, 2]. In a subset of patients where the lesion is confined to the bronchial lumen, endobronchial resection can be a less invasive and parenchyma sparing alternative [8]. Systemic chemotherapy with radiotherapy can be considered in patients with advanced unresectable progressive pulmonary carcinoid [2].

The coexistence of lung cancer with tuberculosis and NTM is well known but the coexistence of bronchial carcinoid with tuberculosis or NTM is rare and has been reported previously in a few cases in the English literature.

Agave et al. reported about 9 cases of pulmonary carcinoids with MTB [9], Yilmaz et al. reported a case of a typical pulmonary carcinoid with tuberculosis in the same lobe [10] and Dixi et al. reported a case of a typical carcinoid in a lower lobe and tuberculosis in the ipsilateral upper lobe [3]. Nakamora et al. reported two cases of atypical mycobacteria with typical pulmonary carcinoids [11]. Mullick et al. reported a case of carcinoid tumor coexisting with both tubercular lesions in the same lobe, as well as regional metastasis [7]. Nagai et al. reported a case of pulmonary tumorlet with caseous granuloma associated with a NTM [12]. Kono et al. reported a case of atypical carcinoid with tuberculosis [13] (Table 1). Here, we report a case of atypical bronchial carcinoid with coexisting mycobacterial infection, either tuberculosis or NTM infection.

Tuberculosis has been described in association with various forms of lung malignancies. However, its association with carcinoids has been rarely reported possibly because the pulmonary carcinoid tumors are rare tumors [3].

Unfortunately, the mycobacterial culture remained negative. Several explanations are possible. First, there could be a sampling error due to uneven distribution of mycobacteria in tissue samples and/or the presence of extensive necrosis in the tissues [14]. Second, a technical problem with the culture such as the presence of a growth inhibitor could explain the negative culture. And third, the sample sent for culture could have been inadequate. In addition, there is also a remote possibility that the Ziehl-Neelsen was false positive because of contamination of the specimen by acid fast bacilli.

There are some next generation sequencing techniques emerging for the diagnosis of microorganisms in the tissue. However, a major concern is the abundance of the microorganism DNA in the tissue. Advantages of such techniques are mainly the possibility of testing multiple microorganisms in one run (multiplex testing). In our case, the low amount of the mycobacterial DNA in the necrosis likely led to false negative results using rtPCR, a lot more sensitive technique.

This case illustrates the importance of systematic examination of the resection specimen with careful attention of the lung parenchyma distal to the bronchial carcinoid. Findings such as mycobacterial infection may require additional treatment and should not be missed.

Bronchial carcinoid is often associated with postobstructive bacterial pneumonia, but can sometimes also coexist with tuberculosis or NTM infection. It is therefore important not only to investigate the resected tumor, but also the obstructed lung parenchyma in the surgical resection specimen.