Fibromatosis colli of infancy

A four-week old neonate was referred to the radiology department for evaluation of a left-sided neck swelling and restricted neck movement on the affected side. The parents had noticed it two weeks ago. On clinical examination, the swelling was hard in consistency and was not warm whentouching it. The child had an assisted delivery by vacuum extraction.

Ultrasonography (USG) showed a fusiform enlargement of the left sternocleidomastoid muscle (Fig. 1), fusiform shaped and heterogeneous in echotexture when compared to contralateral muscle (Figs. 1, 2). The fibrillar structure of the muscle fibers was maintained. There was no cervical lymphadenopathy. Based on these clinical and USG findings, a diagnosis of fibromatosis colli of infancy was made.

Fibromatosis colli is a neonate medical entity, presenting classically as a unilateral neck swelling in the first month of birth. This swelling, being secondary to a fibroblastic proliferation, is considered a benign soft-tissue tumour. Its aetiology is not totally known, however a fibrous reaction secondary to a severe muscular stretching is the most accepted theory. Characteristically, a sternocleidomastoid (SCM) injury during a laborious delivery is the trigger event to this abnormal cellular proliferation. The diagnosis can be made clinically by a typical presentation after a difficult delivery, with a reasonable accuracy, however imagiologic characterisation is mandatory in order to exclude other diagnosis. USG typically confirms the diagnosis when describing a unilateral spindle-shaped thickening of the SCM. Its dependence on the muscular structures can be established by the synchronous movement of the mass with SCM’s contraction. The lack of involvement of any surrounding structure (such as bone or vessels), and the absence of any cervical lymphadenopathy are other remarkable features that distinguishes this entity from other neck masses [1]. In exceedingly doubtful cases, CT scan and MRI can also be helpful [2]. On CT scan, this muscle swelling appears as an isodense diffuse enlargement of the SCM. The children’s exposition to radiation is the drawback of this technique. On MRI, a slightly decreased signal intensity of the mass on T2W-images compared to gradient-recalled T1W-images, reflects the presence of a fibroblastic proliferation. This modality also allows for a better mass-localisation within the SCM and is the better exam to confirm the non-involvement of adjacent structures [3]. Treatment modalities include conservative and invasive ones. Physiotherapy and neck stretching exercises, as conservative approaches, are the preferred modality of treatment. By 4 to 6 months, a swelling regression with complete resolution of the clinical picture is expected. In the uncommon refractory cases to a conservative approach, the use of intramuscular Botulinum toxin type A usually avoids the need of surgical treatment. Surgery remains the last resort for treatment of this condition, consisting of a SCM tenotomy [4]. Written informed patient consent for publication has been obtained.