Fibromatosis Colli


KEY FACTS

Terminology

  • Benign fibrosis of sternocleidomastoid (SCM) muscle

  • Most common cervical “mass” of infancy: Postulated to be muscular response to birth trauma or peripartum injury

Imaging

  • Often diagnosed clinically without imaging

  • Ultrasound modality of choice when imaging required

  • Process entirely intramuscular (contained within SCM), without local invasion or inflammatory changes

  • Fusiform expansion of central SCM muscle

    • Thick & short compared to contralateral SCM

  • Variable heterogeneity of lesion with loss of normal muscle architecture

    • Ranges from nearly homogeneous to markedly heterogeneous on US/CECT/MR

  • Variable internal vascularity within/about mass

  • Fascial planes surrounding SCM preserved

  • No associated adenopathy or fluid collection

Top Differential Diagnoses

  • Cervical lymphadenopathy

  • Infantile hemangioma

  • Cervical teratoma

  • Congenital neuroblastoma

  • Rhabdomyosarcoma

  • Branchial cleft anomalies

  • Lymphatic malformation

Clinical Issues

  • Peak presentation at 24 days old

    • Painless palpable mass with torticollis

    • Contralateral occipital flattening (plagiocephaly)

  • Treatment: Self-limited, usually resolves by 6 months of age

    • 90% fully recover with conservative treatment & physiotherapy

    • Surgery only in unusual cases when craniofacial asymmetry or refractory torticollis persists after 1 year

AP radiograph of the neck shows mild torticollis with the left ear closer to the left shoulder & the chin slightly turned away. No bony anomalies are seen to explain this neck positioning in this infant with fibromatosis colli.

Split screen transverse US images in a 3-week-old girl with torticollis show a homogeneously enlarged right sternocleidomastoid (SCM) muscle
as compared to the left
, typical of fibromatosis colli.

Orienting the US transducer along the long axis of the SCM optimally shows the mildly heterogeneous enlargement/expansion of the muscle belly with normal SCM tapering ends
& sharp, distinct borders
.

Coronal STIR MR in an infant with obvious torticollis shows heterogeneously increased signal intensity & thickness of the left SCM
in a patient with fibromatosis colli. Note the normal right SCM
.

TERMINOLOGY

Synonyms

  • Sternocleidomastoid (SCM) pseudotumor, SCM tumor of infancy, congenital muscular torticollis, neonatal torticollis

Definitions

  • Most common cervical “mass” of infancy

  • Represents benign fibrosis of SCM muscle, typically in response to birth trauma or peripartum injury

IMAGING

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