Cytodiagnosis of 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.

Introduction

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.[12] This lesion is very rare, around 0.4% live birth.[1-3] However, SCMI is the most common cause of congenital muscular torticollis accounting for 10-20% of the cases.[4] The lesion characteristically manifests between the second and eight weeks of life as firm, fusiform, nontender mass of 2-3cm 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. History of complicated delivery and birth injury are associated in more than 50% cases.[5]

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.[6] 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.

Case Report

A two-month-old male child presented with firm fusiform swelling on anterior aspect of neck on right side measuring 2 × 2cm. The swelling was gradually increasing in size. The obstetric history of mother revealed that there was prolonged labor and the baby was delivered by forceps extraction. Post partum period was uneventful.

FNAC was performed from the swelling with 23G 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-Grünwald-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]. Many naked stripped nuclei were seen. 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.

Figure 1

Clusters of spindle shaped fibroblast with wispy cytoplasm along with multinucleated giant muscle cell (Pap stain, ×400)

Figure 2

Myxoid background substances with scanty cellularity representing collagen (Pap stain, ×400)

Discussion

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 pathogenesis of the lesion is still not clear. 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.[124] 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.[36]

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.[2]

FNA cytology is a time saving cost effective reliable diagnostic procedure, and as in this case helped to avoid more invasive procedures. The cytological features include moderate to scanty cellularity of the smears. Cells are predominantly slender, spindle to oval with wispy cytoplasm and nuclei having fine granular chromatin with small to medium sized nucleoli. The cells are usually scattered singly and also in clusters of varying sizes. Atrophic degenerated skeletal muscle, multinucleated giant cells and collagen fibres are seen in varying numbers. Background appears clean and no inflammatory cell components are seen. Mitoses are hardly seen.[1-7]

The cytological differential diagnosis includes all types of benign proliferation of infancy. Nodular fasciitis can be excluded by absence of inflammatory cells and pleomorphic proliferating fibroblast. Infantile fibromatosis shows infiltrative pattern affecting adjacent muscle.[2] Low grade fibrosarcoma/infantile fibrosarcoma rarely affects neck region and shows considerable cellularity and atypia.[27]

FNAC is a safe, minimally invasive, rapid and reliable diagnostic modality for diagnosing sternocleidomastoid tumor of infancy. The typical clinical setting and characteristic cytological findings are definitive of diagnosis.