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 ,
 a 38-year - old man without any symptoms was admitted to our institution because of an abnormal shadow found incidentally on a chest x - ray . 
 chest computed tomography showed a round mass in the lingular segment of the left upper lobe . 
 lingular segmentectomy was performed , and the histopathological diagnosis was intrapulmonary schwannoma . 
 immunohistochemical staining revealed a positive result for s-100 protein and negative results for cd34 and desmin . 
 we report this case of intrapulmonary schwannoma , which is extremely rare . 
Introduction
Case
Discussion