schwannoma may arise from any peripheral nerve and is often found in the chest wall and posterior mediastinum . however , case reports of intrapulmonary schwannoma are extremely rare . a 38-year - old man was referred to our institution because of an abnormal shadow found incidentally on the chest x - ray . the plain chest x - ray showed a mass lesion in the left middle zone . chest computed tomography ( ct ) showed a round and homogeneous mass 25    18  mm in size with a well - defined margin in the lingular segment of the left upper lobe ( fig . 18-fluorodeoxy - glucose ( fdg ) positron - emission tomography ( pet ) showed no accumulation in the tumor ( fig . the ct and fdg - pet findings suggested the possibility of a benign tumor or a low - grade malignancy . as a malignant tumor could not be definitively ruled out , we performed lingular segmentectomy.fig .  1 
 a computed tomography shows a mass with well - defined margins in the lingular segment of the left upper lobe . b 18-fluorodeoxy - glucose ( fdg ) positron - emission tomography ( pet ) showed no accumulation in the tumor 
 a computed tomography shows a mass with well - defined margins in the lingular segment of the left upper lobe . b 18-fluorodeoxy - glucose ( fdg ) positron - emission tomography ( pet ) showed no accumulation in the tumor macroscopic examination of the resected specimen showed a well - demarcated round tumor in the lung , without any evidence of invasion of the surrounding tissues . microscopic examination revealed proliferation of elongated tumor cells having spindle - shaped nuclei , with cellular palisading ( fig . immunohistochemical staining demonstrated positive staining of the tumor cells for s-100 protein and bcl2 , but negative staining for cd34 and desmin . the histopathological diagnosis was intrapulmonary schwannoma.fig .  2 
 a macroscopic examination of the specimen showed a round , well - demarcated tumor in the lung , without invasion of the surrounding tissues . b microscopic examination revealed elongated tumor cells with spindle - shaped nuclei 
 a macroscopic examination of the specimen showed a round , well - demarcated tumor in the lung , without invasion of the surrounding tissues . schwannoma is one of the few truly encapsulated neoplasms of the human body , and is almost always solitary . it most commonly occurs on the flexor surfaces of the extremities , neck , mediastinum , retroperitoneum , posterior spinal roots , and cerebellopontine angle . however , schwannomas are extremely rare in the lung , regardless of the patient age . ohtsuka and colleagues   reported 62 patients ( 28 men , 34 women ) aged 583  years , with intrapulmonary or bronchial schwannomas , and stated that this neoplasm accounted for about 0.2  % of all pulmonary neoplasms . in 55  % of these patients , the tumor originated within the tissues in proximity to the terminal segmental bronchus . on radiographic images , peripheral intrapulmonary schwannoma appears as a round mass with well - defined margins . in patients with the tumor located proximal to a lobar bronchus , atelectasis or pneumonia about half of the patients have some symptoms ; however , most patients with peripheral intrapulmonary schwannomas , as in the present case , have no symptoms . today , fdg - pet is a useful approach to differentiate malignant solitary pulmonary nodules from benign nodules . beaulieu et al . reported the maximum standard uptake values ( suvmax ) of the 10 schwannomas ranged from 1.9 to 7.2 , and the variation in the suvmax could be explained by the variation in cellularity . however , the reason why high fdg accumulation is found in benign tumors such as schwannoma remains unclear , and a diagnostic value of fdg - pet with intrapulmonary schwannoma is not established . it is reported that in rare instances , schwannomas may undergo malignant transformation . the expression level of ki67 , a tumor cell proliferation marker , has been reported to be useful for determining the malignant potential of these tumors . kindblom and colleagues   compared the ki67 expression levels in 26 malignant peripheral nerve sheath tumors and 24 benign nerve sheath tumors ( schwannomas ) , and reported that significantly high density of nuclear staining was found in malignant peripheral nerve sheath tumors . for the treatment of primary intrapulmonary schwannoma , surgical resection , intrabronchial resection with endoscopy , and yttrium aluminium garnet ( yag ) laser resection have been employed [ 57 ] . because of the low malignant potential of these tumors , tumor enucleation or partial lung resection is thought to be adequate , with lobectomy not being necessary . in the present case , we performed segmentectomy to accomplish complete resection , because we did not obtain the pathological diagnosis before the operation and the tumor was located in the central part of the superior lingular segment . in conclusion ,