Fibromatosis colli leading to positional plagiocephaly with gross anatomical and sonographic correlation

Abstract

Fibromatosis colli, also known as ‘sternocleidomastoid tumour of infancy’ or ‘pseudotumour of infancy’, is a rare condition involving fibrosis and swelling, or ‘tumour’ of the sternocleidomastoid muscle in newborns that typically occurs after a traumatic delivery. Although usually self-limited, fibromatosis colli can lead to congenital muscular torticollis and positional plagiocephaly due to uneven forces on the neonatal skull. Ultrasound is the diagnostic imaging modality of choice and can prevent additional imaging and unnecessary intervention.

Background

Fibromatosis colli has a prevalence of 0.4% and is the leading cause of congenital muscular torticollis (CMT), which can lead to craniofacial asymmetry and positional plagiocephaly.^{1 2} It typically presents as a firm, non-tender lump or nodule in the neck between the second and eighth weeks of life.^{3 4} Although the exact mechanism is unknown, the leading hypothesis is that head malposition in utero leads to compression and fibrosis of the sternocleidomastoid (SCM). The classical teaching that birth trauma injures the SCM leading to fibrosis has lost traction recently, with studies showing as many as 25% cases being reported in utero, and independent of delivery method.^{5 6} Despite this, it remains the leading alternative hypothesis.⁶ It occurs on the right side 75% of the time with rare reports of bilateral lesions.^{1 7} Fibromatosis colli affects boys more than girls, with a male:female ratio between 1.5 and 2.3:1.^{8 9} Histologically, fibromatosis colli tumours are characterised by benign spindle fibroblasts and collagen deposition surrounding atrophied skeletal muscle fibres of the SCM.^{9 10}

The most common complications of fibromatosis colli are CMT or a ‘twisted neck’ in which the newborn looks away from the affected side (figure 1) which occurs in 10%–20% of newborns with fibromatosis colli,^{3 4} and plagiocephaly, which occurs in up to 64%–90% of those newborns with CMT.^{4 11}

Figure 1.

A swollen and fibrotic sternocleidomastoid muscle (arrowhead) results in head tilt towards the ipsilateral side, with chin rotation to the contralateral side (arrows). Illustration by Elizabeth Rooks.

Case presentation

A newborn boy was born at 41 weeks 3 days to a primigravida via spontaneous vaginal delivery, weighing 4570 g (10.10 lbs). Delivery was complicated by a 4-minute shoulder dystocia, during which he sustained a left humeral shaft fracture (figure 2). His APGARS were 1¹, 2⁵, 5¹⁰, 6¹⁵, 8²⁰ for poor respiratory effort requiring intubation at 6 min, floppiness and heart rate <100 until 5 min. He was extubated to room air within his first hour of life. His fracture was reduced and treated with a sling-a-swath, which was later transformed into a safety pin from left sleeve to chest. He gradually developed increased movement of his left arm after birth, but at 3 weeks old, his parents noted a lump on his SCM, as well as a preference of looking to his right.

Figure 2.

A conventional radiograph of the left humerus shortly after birth demonstrates a displaced, mid-humeral diaphyseal fracture, indicative of the birth trauma incurred during delivery.

Investigations

On physical examination, he was noted to have right-sided plagiocephaly and a strong preference to turn to his right (figure 3). An ultrasound of the neck revealed a thickened, heterogeneously echogenic left SCM muscle consistent with fibromatosis colli (figure 4), and he was referred to physical therapy.

Figure 3.

On gross examination, there is marked increase in the thickness of the left sternocleidomastoid (SCM) (A) compared with the right (B). Looking at the patient’s face (C), there is a noticeable facial asymmetry, with left mandible flattening and chin deviation to the patient’s right. Viewed from above (D), there is evidence of slight right-sided plagiocephaly, with the right ear being more anterior than the left. (E) Demonstrates the patient’s baseline, preferred position of facing to his right.

Figure 4.

Sonographic imaging of the palpable left neck abnormality demonstrates thickening of the left sternocleidomastoid (SCM) muscle measuring 1.1 cm wide in its longitudinal axis (A) and 1.3 cm in the transverse axis (B). The mass within the left SCM has heterogeneous echotexture, with scant vasculature on Doppler (C) consistent with fibromatosis colli. By comparison, the right (normal) SCM measures 0.4 cm wide in the longitudinal axis (D), and 0.5 cm in the transverse axis (E).

Treatment

The patient attended physical therapy on a weekly basis for range-of-motion and stretching exercises targeting his affected SCM. Additionally, his parents were instructed on how to practise physical therapy manoeuvres at home. Treatment involves monitoring the patient’s plagiocephaly for resolution, and also monitoring for related disorders, such as developmental dysplasia of the hips.

Outcome and follow-up

Now at 6 months after birth, the patient’s fibromatosis colli has resolved, and he is meeting all milestones symmetrically, for example, turning his head in both directions 45 degrees while prone with arms extended and weight bearing. His right plagiocephaly has persisted, but has demonstrated gradual improvement.

Discussion

Fibromatosis colli frequently causes CMT, which can lead to craniofacial asymmetry, and in our case, positional plagiocephaly. Thankfully, as many as 90% of cases respond to conservative treatment with physical therapy, which is the gold standard for treatment. Early initiation of therapy is associated with shorter duration and increased effectiveness.¹²

Although the diagnosis can be made on the basis of history and clinical presentation, non-invasive imaging may be helpful adjunct. Sonographic findings include a diffusely enlarged SCM with a mass with homogeneous echotexture that is isoechoic to normal SCM, with or without a hypoechoic rim.⁷ Real-time ultrasound demonstrates the mass moving synchronously with the SCM.¹³ Ultrasound has a reported sensitivity of 100% for pseudotumor of infancy and is the imaging modality of choice.^{7 14}

Although the differential diagnosis of solid tumours in this location includes rhabdomyosarcoma and neuroblastoma, the history and imaging in this case made the diagnosis of fibromatosis colli clear. Malignancies would be more likely to have findings of enlarged cervical lymph nodes, vascular encasement or invasion of surrounding structures.¹³ Neurological causes of CMT include cranial nerve 11 palsy, which was not suspected based on the clinical presentation and imaging.

Conservative treatment with range-of-motion exercises will result in complete resolution in 80%–90% of cases within infancy.^{14 15} Surgical management involving tenomyolysis, and other interventions such as force redistributing helmets, or even botulism toxin injections are typically reserved for patients that fail conservative management for 1 year.^{8 14 15}

Our patient has demonstrated resolution of his fibromatosis colli, based on diminished mass size, and symmetrical muscle use. His plagiocephaly is also expected to resolve as a result.

Patient’s perspective.

We are immensely grateful for the care my son received, and are relieved that his condition has been gradually improving with conservative therapy. Most of all, we are relieved that he does not require surgery. My son no longer displays any significant preference of turning his head and is showing improved facial symmetry as well.

Learning points.

• Fibromatosis colli is the most common cause of congenital muscular torticollis and can lead to positional plagiocephaly.

• Early recognition can prevent unnecessary workup and can prompt conservative treatment with physical therapy, which has demonstrated excellent response.

• Surgical management should be reserved for refractory cases.