Difficult intubation: 'Beyond the vocal cords'.

Sir,

Endotracheal intubation is a crucial step during anaesthesia. Airway assessment and anticipation of difficult airway are indispensable as part of pre-anaesthetic evaluation. Higher Mallampati score, reduced neck extension, reduced thyro-mental distance and obesity are the factors associated with difficult airway. A series of steps may be required in the management of unanticipated difficult airway.[1] Although common causes of difficult intubation are related to issues of upper airway, causes beyond vocal cords may not be apparent during preoperative evaluation. Such causes include tracheal stenosis, tracheal deviation, tracheal polyps and tumours. We recently encountered a patient with an unusual cause of difficult intubation.

A 48-year-old previously healthy asymptomatic woman was taken up for surgery (renal donor) under general anaesthesia. Her general physical examination was unremarkable and chest radiograph was normal. After pre-oxygenation and induction, of anaesthesia endotracheal intubation was attempted but could not be performed as the tube could not be advanced beyond the vocal cords. The anaesthetist noticed mucosal irregularity in the tracheal wall beyond the cords on laryngoscopic examination. As the diagnosis was not clear and an infective pathology was suspected. Intubation with a smaller tube was not attempted, surgery was abandoned and the patient was referred to pulmonary medicine services for further evaluation. Flexible bronchoscopy performed on outpatient basis demonstrated multiple variable-sized nodules in the tracheal wall involving anterior and lateral walls with sparing of posterior wall [Figure 1]. Bronchoscopic biopsies of the nodular lesions which were stony hard in consistency were obtained with difficulty. A diagnosis of tracheobronchopathia osteochondroplastica (TPO) was considered based on the visual findings. This was confirmed when histopathological examination revealed fragments of bronchial mucosa with bone and intertrabecular marrow in the subepithelium. As the patient was asymptomatic and there was no significant central airway obstruction, a decision for observation was taken. The patient was referred back for surgery with advice to use a small-sized endotracheal tube during the procedure.

Figure 1

Bronchoscopic view of multiple variable-sized hard nodules in the trachea

TPO is an uncommon cause of difficult intubation. It is a rare, benign airway disorder characterised by the development of nodular projections in trachea or bronchi characteristically sparing the posterior membranous tracheal wall. As it is mostly asymptomatic, diagnosis is often delayed. Diagnosis is usually not apparent on chest radiograph unless extensive tracheal calcifications are present, and most often, it is incidentally diagnosed during computed tomography (CT) scan or bronchoscopy. CT usually demonstrates beaded calcification in the tracheobronchial cartilage. Virtual bronchoscopy with three-dimensional reconstruction of CT images is very useful in the assessment of airway involvement in such cases. In symptomatic patients, shortness of breath, noisy breathing, change in voice and haemoptysis may occur. Bronchoscopic appearance is characteristic showing multiple nodules in the cartilaginous part of trachea and main bronchi. Histopathological confirmation of diagnosis is preferable but not essential in view of characteristic bronchoscopic appearance. Differential diagnoses include amyloidosis, papillomatosis, granulomatosis with polyangiitis, endobronchial tuberculosis and sarcoidosis. The cause and pathogenic mechanism of the disease are unclear. Genetic factors, mycobacterial infections and exposure to chemical or mechanical irritants such as silica have been thought to be causative factors. We recently reported a patient with TPO following laryngeal tuberculosis.[2]

Treatment is usually conservative and long-term follow-up has shown that these patients may remain relatively asymptomatic for long durations.[3] Uncommonly, diagnosis is made incidentally during difficult intubation.[456] As it is a benign disorder and most patients are asymptomatic, no immediate treatment is warranted and patients can be kept under follow-up. If there is significant airway narrowing, surgical, radiation [7] or bronchoscopic interventions (such as forceps removal, laser ablation or cryoprobe removal of the obstructing nodules) may be required.

This case highlights that TPO should always be considered as a differential diagnosis of difficult intubation. Laryngeal mask airway may be an acceptable alternative in patients with non-critical obstruction. Smaller-sized endotracheal tube can be used, and in a patient with established diagnosis of TPO undergoing surgery, a difficult airway management plan should always be in place.

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