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Fibromatosis colli (FC),
also known as 'sternocleidomastoid tumour of infancy', is a benign spindle
cell lesion of the sternocleidomastoid muscle. It is often associated with
torticollis due to contraction of the sternocleidomastoid muscle.
Although the
pathogenesis of this lesion is not clear, it is probably related to birth
trauma (breech or forceps delivery). Injury leads to secondary pressure necrosis and fibrosis within the muscle. In the early stage the
mass may grow rapidly. Later the growth slows and ultimately
ceases. After a period of 1 to 2 years it begins to regress . About 2/3rd of the cases resolve spontaneously.
Age:
Most cases show no abnormality at birth but manifest between
the 2nd and 4th week of life. Fibromatosis
colli affects male patients slightly more often than female
patients.
Site:
The lesion presents as a firm soft-tissue mass in the
lower one-third of the sternocleidomastoid muscle. The disease
is usually unilateral (slightly more common on the right
side) and affects both the sternal and clavicular heads of the
muscle. Bilateral involvement is rare.
Gross:
The mass may be excised
at an early stage. Macroscopically it is a small firm mass (2-3 cm in
diameter), with a greyish white, glistening cut surface . The lesion
blends with the surrounding smooth muscle.
Microscopic features:
IMAGE1
IMAGE2
1. There is replacement
of muscle fibres by hyalinized fibrous tissue.
2. Throughout the lesion there are scattered residual muscle fibres which
shows prominent degenerative
and reactive changes (atrophy, swelling, loss of cross striations). There
is little cellular pleomorphism or mitotic activty.
Differential diagnosis:
Myositis ossificans
progressiva ; Desmoid type fibromatosis:
(Unlike fibromatosis colli damaged muscle fibres are not present in
fibromatosis.)
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