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sternocleidomastoid tumor of infancy ( scmi ) , also known as fibromatosis colli or muscular fibromatosis of infants , is a benign self limiting fibroblastic lesion involving body of sternomastoid muscle .
this lesion is very rare , around 0.4% live birth.[13 ] however , scmi is the most common cause of congenital muscular torticollis accounting for 10 - 20% of the cases .
the lesion characteristically manifests between the second and eight weeks of life as firm , fusiform , nontender mass of 2 - 3 cm diameter involving mid or lower part of sternocleidomastoid muscle .
the right side is more commonly affected than left and males are affected more than females .
management of scmi in majority of cases being conservative , fine - needle aspiration cytology ( fnac ) , as a minimally invasive cost effective and time saving outdoor diagnostic procedure , has an important role to play .
the differential diagnosis includes various congenital , inflammatory lesions , neoplastic conditions- both benign and malignant and other forms of infantile fibromatosis that may occur at that site .
the diagnosis of scmi is based on characteristic clinical presentation and cytological features that discriminates it from others .
we report a case of two - month - old baby diagnosed as scmi on cytology .
a two - month - old male child presented with firm fusiform swelling on anterior aspect of neck on right side measuring 2  2 cm .
the obstetric history of mother revealed that there was prolonged labor and the baby was delivered by forceps extraction .
fnac was performed from the swelling with 23 g needle and 10 ml plastic disposable syringe .
the wet smears were fixed in 95% ethanol and processed for papanicolaou stain and the air dried smears were stained with may - grnwald - giemsa stain .
microscopy showed moderately cellular smear composed of oval to spindle shaped fibroblastic cells scattered singly or in loose cohesive clusters .
cells were having plump oval to spindle nuclei with wispy cytoplasm [ figure 1 ] .
background was clean with focal areas showing myxoid material [ figure 2 ] . based on above cytological finding ,
a diagnosis of sternocleidomastoid tumor of infancy was suggested , and the patient was managed conservatively .
clusters of spindle shaped fibroblast with wispy cytoplasm along with multinucleated giant muscle cell ( pap stain , 400 ) myxoid background substances with scanty cellularity representing collagen ( pap stain , 400 )
sternomastoid tumor of infancy is a rare and self limiting entity and has characteristic clinical presentation such as age , sex , site of lesion and history of birth trauma .
the different theories proposed to explain the pathogenetic mechanism , include fetal malposition , birth trauma , ischemic necrosis following vascular compression during birth , infection and presence of endogenous factor . a well recognized association between scmi and primiparous birth , breech presentation , forceps
deliveries and difficult labour are found . the lesion is often diagnosed clinically by its classical presentation and physical examination .
the clinical differential diagnosis includes various congenital lesions such as branchial cyst , thyroglossal cyst and inflammatory condition like tuberculous lymphadenitis , benign neoplastic condition like hemangioma , cystic hygroma and malignant neoplasm like neuroblastoma , rhabdomyosarcoma and lymphoma .
radiologic imaging modalities such as ultrasonography and computed tomography are helpful in locating the exact tumor site and in differentiating solid and cystic nature of the lesion . surgical diagnostic biopsy may result in complication such as cosmetic defect due to contracture band and is reserved for difficult cases .
fna cytology is a time saving cost effective reliable diagnostic procedure , and as in this case helped to avoid more invasive procedures .
cells are predominantly slender , spindle to oval with wispy cytoplasm and nuclei having fine granular chromatin with small to medium sized nucleoli .
atrophic degenerated skeletal muscle , multinucleated giant cells and collagen fibres are seen in varying numbers .
mitoses are hardly seen.[17 ] the cytological differential diagnosis includes all types of benign proliferation of infancy .
low grade fibrosarcoma / infantile fibrosarcoma rarely affects neck region and shows considerable cellularity and atypia .
fnac is a safe , minimally invasive , rapid and reliable diagnostic modality for diagnosing sternocleidomastoid tumor of infancy .
sterocleidomastoid tumor of infancy ( scmi ) , also known as fibromatosis colli of infancy , is a benign , self limiting disease of new born characterised by its classical history and clinical presentation of firm to hard fusiform mass in the lower and middle portion of sternocleidomastoid . 
 scmi often appears during early perinatal period between second to fourth weeks of life . a well recognized association between scmi and primiparous birth , breech presentation , prolonged difficult labor and forceps deliveries is found . 
 cytology shows spindle shaped mature fibroblastic cells scattered singly along with degenerated and multinucleated giant muscle cells in a clean background . 
 it is important to differentiate this lesion from different forms of infantile fibromatosis . 
 fine - needle aspiration cytology ( fnac ) , as a time saving , rapid and reliable diagnostic procedure , has got bigger role to play in reassurance of anxious parents , guiding for conservative management and avoiding surgery .