DISCUSSION
Schwannoma and neurofibroma arise from peripheral nerves. Schwannoma usually occurs in head, neck, retroperitoneum, extremities and mediastinum.9 Tracheal schwannoma is rare and was first reported by Straus et.al in 195110 and is believed to originate from nerves inside the tracheal wall.2 Schwannoma is common in adults with female predilection.4 It is frequently found in the lower third of the trachea followed by proximal trachea and middle third of trachea.11
Symptoms are misleading in these patients as clinicians mistake dyspnea, wheezing or cough caused by tracheal neoplasm for symptoms of COPD which causes delay in diagnosis of 10-15 months in average.12 Hemoptysis is uncommon symptom for schwannoma and is predominantly found in squamous cell carcinoma.6
In spirometry, characteristic flow-volume loop with flattened inspiratory and expiratory limbs is suggestive of fixed upper airway obstruction.13 CT scan in Schwannoma demonstrates well-demarcated, low density mass prior to contrast and contrast enhancement after injection of the contrast. CT is essential as it helps to define the location of tumor and allows assessment of luminal and extrinsic extent of tumor.5 Bronchoscopic evaluation is indispensable in the localization of the tumor in relation to cricoid and carina, to determine the length of the luminal disease, assessment of distal bronchial tree and biopsy of the tumor as well. Assessment of vocal cord function is important as thyroid carcinoma associated with tracheal invasion is seen in about 6% of patients presenting for resection and anastomosis.14 MRI shows isointensity or hypointensity on T1 weighted images and hyperintensity on T2 weighted images with heterogenous enhancement.12
According to Kashara et.al15 pulmonary neurilemmomas can be divided into two types a) Central type b) Peripheral type. In terms of relationship between tumor and tracheal luminal space, central type is further classified into two subtypes 1) Intraluminal type- tumor is confined in the intraluminal space 2) Transmural type- tumor occurs in both intraluminal space and extraluminal space(combined type). We encountered a transmural type of tracheal schwannoma with extraluminal component contiguous to the left thyroid lobe.
Treatment of tracheal schwannoma can either be endoscopic resection or surgical resection based on size, location and extent of the tumor. Endoscopic treatment does not always achieve or confirm complete resection and is applicable in patients with pedicled and intraluminal type tumor, patients with advanced age, limited life expectancy, with severe co-morbidity and in whom complete resection cannot be offered.16 Complete resection of tracheal schwannoma with bronchoscopic technique has been reported17 but one should always look out for local recurrence. Local destruction of tumor by core out, Nd:YAG laser ablation, cryotherapy and primary radiotherapy by external beam can be used in addition or as as alternative to endoscopic resection as a tool to relieve the airway obstruction caused by tracheal neoplasm.9,11,15,16Surgical resection and anastomosis has been the optimal management where tumors are sessile and broad based, transmural type tumor, in patients with preserved cardio-pulmonary function and in recurrent schwannoma.9,16