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Musculoskeletal » Neck / Head
Fibromatosis coli
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Author(s) :
Pamela T. Johnson, MD
Presentation This six week old boy was found to have a palpable left sided neck mass by his mother.
Caption: Sagittal image of the left neck.
Description: Ultrasound demonstrates a 1.9 cm long solid, mildly hypoechoic and heterogeneous mass in the left neck.
Caption: Sagittal image of the left neck.
Description: Sagittal sonogram shows that the mass is intramuscular, within the left sternocleidomastoid muscle.
Caption: Color Doppler of the mass.
Description: Color Doppler demonstrates vascularity within the intramuscular mass.
Caption: Spectral Doppler of the mass.
Description: Spectral Doppler documents arterial flow within the mass, demonstrating high-resistance flow.
Caption: Sagittal image of the left neck.
Description: This sagittal image confirms the intramuscular location of the elongated mass within the sternocleidomastoid muscle.
Caption: Transverse image of the thyroid.
Description: Sonogram shows a normal thyroid. This confirms that the mass is not of thyroid origin.
Differential Diagnosis Fibromatosis coli
Intramuscular hematoma
Final Diagnosis Fibromatosis Coli
Discussion Fibromatosis coli is also known as 'pseudotumor of infancy'. It is associated with congenital muscular torticollis. A palpable mass within the sternocleidomastoid (SCM) muscle is discovered in 63% of cases. Infants with this condition often present with head tilt (90%) toward the side where the mass is located. The chin tilts in the other direction. This results from contracture of the SCM muscle. Approximately 40% have plagiocephaly. In addition, 10% have congenital hip dysplasia. Infrequently, feeding difficulty and facial asymmetry may be present. The average age at which this condition is discovered is 4 months, but it may be as early as 2-4 weeks after birth.

If a neck mass if found on physical examination in an infant, the differential diagnosis would include a thyroglossal duct cyst (midline), teratoma, cystic hygroma (often posterolateral), branchial cleft cyst (lateral) and fibromatosis coli (lateral), as well as the rare rhabdomyosarcoma. However, the ultrasound appearance shown in this case suggests the diagnosis of fibromatosis coli. A well marginated, nearly isoechoic solid mass is causing fusiform enlargement of the sternocleidomastoid muscle. Spectral Doppler of the mass demonstrates high-resistance flow, thus decreasing the probability of a malignant tumor.

Several causes are hypothesized. Intrauterine positioning may result in fibrosis and contracture of the SCM muscle. This would explain the associated plagiocephaly and congenital hip dislocation. In some cases, the mass may result from birth trauma and hematoma formation in the muscle. In these cases, the intramuscular hematoma will generally present a complex pattern (partly cystic and partly solid).

Once the diagnosis is made, treatment is extremely important to eliminate the torticollis. Passive range of motion exercises are performed on the neck. This results in resolution of the condition in most cases. If this fails, muscle release or tenotomy may be necessary. The outcome overall is total resolution in 86% of cases, subtotal resolution or long term abnormality in 14%.

Because of the association with congenital hip dysplasia, this must be excluded with physical examination and/or ultrasound of the hips.

Case References Wei JL, Schwartz KM Weaver AL and Orvidas LJ. Pseudotumor of infancy and congenital muscular torticollis: 170 cases. Laryngoscope 111(4): April 2001, 688-695.
Follow Up The mass decreased in size over time. Passive range of motion exercises prevented any significant torticollis.
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