schwannomas are benign tumors that originate from nerve sheaths composed exclusively of schwann cells8910 ) . a major - nerve , intramuscular schwannoma is an extremely rare condition9 ) . due to low frequency of this tumor type and lack of specific instrumental signs and symptoms , we present a rare case of intramuscular schwannoma originating from the dorsal ramus nerve in a 62-year - old woman . a 62-year - old woman patient was admitted to the hospital because of a palpable back mass on her left side . the mass was identified eight years prior , and grew slowly , until pain developed upon touch five years prior . the mass was observed in the left erector spinae muscles ( in the l2 - 4 region ) by magnetic resonance imaging ( mri ) . t2- and t1-weighted images showed heterogeneous high signal intensity , and intermediate to low signal intensity , respectively ( fig . 1 ) . the preoperative diagnostic evaluation suggested the growth was metastasis , sarcoma , or a peripheral nerve sheath tumor . the lesion was thought to originate on the cranial side , and was completely removed , including the origin . when the mas was cut , the surface of the mass was mottled , whitish pale - yellow , and myxoid with hemorrhagic foci ( fig . microscopically , the tumor was composed of compact spindle cell regions ( antoni - a ) , with a nuclear , palisading and whirling cell pattern , and loosely arranged areas of lower cell density ( antoni - b ) , along with ectatic , irregularly - shaped hyalinized vessels ( fig . the most common types of benign soft tissue tumor are lipoma and related variants ( 16% ) , and other types include fibrous histiocytoma ( 13% ) , nodular fasciitis ( 11% ) , hemangioma ( 8% ) , and schwannoma ( 5%)5 ) . approximately 25 and 45% of schwannoma cases occur in the head and neck areas , respectively12 ) . the symptom frequencies reported among patients with benign schwannoma are 5 - 52% for tenderness , 20% for radicular pain , 60 - 96% for the tinel sign , and 7.6 - 82% for motor weakness6 ) . intramuscular schwannomas are highly uncommon ; however , reports have been documented for such tumors originating from the psoas and coracobrachialis muscles , with palpable masses that presented with either no symptoms or lower extremities numbness , but no characteristic symptomatic features12489 ) . schwannomas typically originate from a small nerve branch within the muscle , and symptoms vary depending on the site of origin6913 ) . because intramuscular schwannomas originate from motor branch nerves , neurological symptoms , including pain , motor weakness , paresthesia , are rare69 ) . in our case , there was no radicular pain or motor weak ness ; however slight tenderness was reported . in our patient the erector spinae muscles are dominated by the lumbar dorsal ramus nerve , which branches to form the spinae nerve . the dorsal ramus nerve runs dorsocaudally in the transverse domain , and generally separates into the medial , intermediate , and lateral branches3 ) . schwannomas are typically well encapsulated and solid with membranes composed of a thin fibrous capsule pressing on perineural tissue12 ) . however , if a schwannoma is large , it appears heterogeneous in radiological exams , indicating hemorrhage and tissue necrosis1 ) . in the present study the histological hallmark of a schwannoma is varying proportions of two distinctive tissues : fascicular type ( antoni - a ) and reticular type ( antoni - b)911 ) . antoni - a is highly cellular , with compact , spindle - shaped cells17911 ) . immunohistochemically , schwannomas typically show diffuse , strongly s-100 protein expression11 ) . in the present case , we cautiously removed the encapsulated mass and excised the origin , which appeared to be the dorsal ramus nerve . our tissue biopsy confirmed the presence of a very rare intramuscular benign schwannoma , with typical features . to our knowledge , this is the first report of a dorsal ramus nerve schwannoma within the erector spinae muscles . when a patient has palpable , deep or intrinsic back muscle tissue mass , a radiological examination , such as a computed tomography ( ct ) or mri should be considered . in the ct or mri , a distinct pattern in the surrounding wall of the mass is suggestive of schwannoma , which we confirmed by needle biopsy . if histological findings suggested the presence of antoni - a or -b and the s-100 protein is strongly expressed , a diagnosis of dorsal ramus schwannoma should be considered .
we present a rare case of intramuscular schwannoma originating from the dorsal ramus nerve in a 62-year - old woman . 
 the mass grew slowly , with pain developing upon touch five years prior . 
 no neurological deficit was detected . 
 the mass was observed in the erector spinae muscles in magnetic resonance imaging ( mri ) , and surgical excision was performed . 
 the mass was well encapsulated with clear margin . 
 the lesion appeared to originate from the cranial side . 
 we completely removed the mass including the origin . 
 histopathology confirmed a schwannoma diagnosis . 
 this is the first report , to our knowledge , of a dorsal ramus - nerve schwannoma within the erector spinae muscles .