fibroma of the tendon sheath ( fts ) is a rare benign soft tissue tumor ( sts ) , typically attached to the tendon sheath . although histology of fts has been adequately described in the literature , yet diagnostic cytologic criteria have not been studied well . to the best of our knowledge , only two studies in english describe the fine - needle aspiration cytology ( fnac ) findings of fts in three cases . fts may not be accurately diagnosed by fnac , because of frequent overlapping of cytologic features with other benign or low - grade firbo myxoid stss . here a case of fts is presented with discussion on cytologic features and its differential diagnosis . a 50-year - old female presented with a slow growing , painless , and firm nodule on the right thigh since 2 years . physical examination revealed a 3.2 cm  3.0 cm  2.5 cm sized , solitary firm nodular swelling , without skin involvement , on the ventral aspect of the right thigh , 7 cm above the knee joint . the swelling could be moved in transverse direction , but was fixed in a vertical direction and in the flexion state of the knee joint . fnac of the swelling was performed using a 22-gauge needle attached to a 10 ml disposable syringe . hematoxylin and eosin ( h and e ) stained smears showed few loose clusters and singly dispersed bland appearing fibrotic spindle cells and stellate cells admixed with hyalinized fibro - collagenous matrix . spindle cells had oval to elongate nuclei , fine nuclear chromatin , and variable amount of ill - defined cytoplasm . necrosis and atypical mitoses were not seen [ figure 1 ] . in correlation with clinical findings , cytological features were suggestive of a benign / low - grade fibroblastic or fibromyxoid lesion ( without further specification ) . fine - needle aspiration cytology , ( a ) scanty cellular smear shows loose cellular clusters with clumps of fibro - collagenous matrix ( h and e , 100 ) . ( b ) many bland appearing fibrotic spindle and stellate shaped cells are embedded in a hyalinized fibro - collagenous matrix ( h and e , 200 ) [ inset : spindle cells show mild nuclear pleomorphism with irregular nuclear contour , fine chromatin and variable ill - defined cytoplasm ( h and e , 400 ) ] . ( c ) myxoid substance with few fibrotic spindle cells ( h and e , 200 ) the patient underwent excision biopsy of the mass with free margins . a well - circumscribed , firm , glistening white nodular mass was received measuring 3.0 cm  2.7 cm 2.0 cm . cut surface showed solid homogenous , grayish - white , and minimal whorled appearance . central area was composed of intersecting bundles and haphazardly arranged spindle - shaped fibroblasts and stellate - shaped cells in a dense eosinophilic hyalinized fibro - collagenous stroma . peripheral area was less cellular with few cleft / slit - like vascular channels in a loose fibro - collagenous and myxoid matrix . spindle - shaped fibroblasts showed elongate nuclei with smooth contour , fine nuclear chromatin , occasional distinct small nucleoli and amphophilic cytoplasm . histology , ( a ) cellular area shows intersecting bundles and haphazardly arranged spindled fibroblasts and stellate cells in a dense hyalinized fibro - collagenous stroma ( h and e , 100 ) . ( b ) hypocellular area shows few slit - like vascular channels in a loose fibro - collagenous matrix with few bland appearing spindled fibroblasts and stellate cells ( h and e , 100 ) . few cells show mild nuclear pleomorphism ( h and e , 200 ) the postoperative course was uneventful . at 1-year follow - up , fts commonly presents as a solitary firm , slow growing , and painless mass of long duration , ranging in size from 0.5 cm to 5.5 cm . fts rarely originate from the synovial membrane of the joint capsule and present as an intra - articular mass with movement restriction . although fts can occur at any age , its peak incidence is between 20 years and 50 years with male predominance . most patients are asymptomatic . however , approximately one - third of the patients present with discomfort and mild pain due to compression of underlying nerves . magnetic resonance imaging ( mri ) is a useful imaging technique prior to surgery but a definitive diagnosis of fts can not be made . fnac is an investigation of choice in many ssts , considering its ability to differentiate between benign and malignant stts in most cases and subsequent impact on management . some reactive and benign lesions ( such as nodular fasciitis , schwannoma , fibrous , and myxoid tumors ) may contain atypical cells . differentiation of such reactive / benign tumor from low - grade stts is a challenging issue solely on the basis of cytology . in such instances , an intermediate diagnosis  benign / low - grade spindle cell tumor cytological features of three previously reported cases of fts including present case are as follows : 
 a hypocellular smear;bland fibroblast - like spindle cells having oval to elongate nuclei and variable amount of ill - defined cytoplasm;few clumps of hyalinized fibro - collagenous stroma ; anda rare myxoid substance . 
  a hypocellular smear ; bland fibroblast - like spindle cells having oval to elongate nuclei and variable amount of ill - defined cytoplasm ; few clumps of hyalinized fibro - collagenous stroma ; and a rare myxoid substance . fts usually yield low cellularity , which may be one of the limiting factor for achieving a correct diagnosis . thin vascular channels , represented as elongated slit - like / cleft - like spaces on histology , are not seen on cytology smears of all cases including present case . myxoid change can be seen in a variety of stts and it is not a diagnostic feature for any stts . some ftss may display mild degree of nuclear atypia ; however , necrosis and atypical mitoses are typically absent . in the present case , cytological features of fts overlap with those of schwannoma , benign fibrous histiocytoma , fibromatosis , desmoid fibromatosis , intramuscular myxoma , nodular fasciitis , low - grade fibromyxoid sarcoma ( lgfms ) , and myxofibrosarcoma . it is important to differentiate fts from lgfms and myxofibrosarcoma because of different prognosis and management . lgfms usually show hypercellular cohesive tissue fragments of spindle cells and hypocellular zone of myxoid matrix with few dispersed single cells . though mild nuclear atypia is common , necrosis and atypical mitoses are typically not seen . myxofibrosarcoma show two types of malignant cells : an elongated , spindle - shaped , fibroblast - like cell and a larger , histiocyte - like cell . . fragments of curvilinear capillary vessels in an abundant myxoid matrix are seen in the background . in difficult cases , marginal excision of fts with preservation of important anatomical structures gives an extremely low recurrence rate and excellent outcomes . incomplete excision of the lesion may lead to recurrence in approximately 24% of the cases within months to years after the diagnosis was made , sometimes repeatedly , but nondestructively . fts can show mildly atypical spindle cells with fibro - collagenous and myxoid material , which may create a diagnostic challenge on cytology particularly in separating benign from low - grade stts . the role of fnac should be limited to differentiate benign from malignant stts including low - grade stts , due to different prognosis and management .
fibroma of the tendon sheath ( fts ) is an uncommon benign soft tissue tumor ( sts ) of the tendon sheath . 
 clinical and radiological features are not distinctive enough to clinch the diagnosis preoperatively . 
 although histological features are well described , diagnostic cytological features of fts are still lacking . till date 
 only two reports describe the fine - needle aspiration cytology ( fnac ) findings of fts . 
 the present case is a 50-year - old female who presented with a slow growing nodule on the right thigh over a period of 2 years . 
 fnac revealed low cell yield with loose clusters of fibrotic spindle cells and stellate cells intermingled with fibro - collagenous and myxoid matrix . 
 few cells showed mild degree of nuclear atypia . 
 necrosis and atypical mitoses were not seen . 
 cytology findings were suggestive of benign / low - grade fibroblastic or fibromyxoid lesion . 
 histology confirmed the diagnosis of fts . 
 this article discusses the diagnostic role of fnac in fts with its differential diagnosis