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Column originally published Apr 24, 2007

A Neck Lump In A Newborn Baby Is Likely Benign

Question: Our son is two months old. Three weeks ago, I suddenly found a lump in his neck. I was very scared, and immediately contacted my family doctor. She carefully examined him and told me that it was likely the result of an injury to his neck muscle during delivery. I had a rather long labour. By the time when his head came out, I was totally exhausted. My doctor had to pull him out, and I was not much of help by that time. She suspected the pulling that she had to do caused a little tear in the muscle of his neck, and this lump developed as a result of the injury. We were very lucky that our doctor was able to arrange an ultrasound of the lump within one week, which confirmed that the lump was in the muscle. However, some of our family members feel that we should request more tests and a referral to other specialists, just in case if this lump is cancerous. We don’t want to do too many tests on him because he is so young. Are we putting our son in danger with our decision?


I think you can calm down and relax.  Your doctor has done a wonderful job in making and confirming the diagnosis.  From your description, the lump that you had discovered is called sternomastoid tumour.  Please do not be concerned about the word tumour, it has nothing to do with cancer.

Many years ago, doctors did not have powerful tools like what we have today.  When parents found similar lumps and seek advice from their physicians, they didn’t have a good explanation except they knew from experience that these lumps would gradually disappear over several months.  They knew these lumps were attached to the sternomastoid muscle in the front part of the neck.  That is the reason why it is called sternomastoid tumour.

The cause of sternomastoid tumour is not completely clear.  In some situations, if the doctor has to stretch a baby’s neck during delivery, the sternomastoid muscle can be stretched a little too much, resulting in little tears in the muscle fibers.  When these muscle fibers start to heal, collagen and other fibrous tissues deposit at the injury site, causing a lump to appear.  Over time, when the healing is complete, the lump will disappear.  This is similar to the healing of a bone fracture.  When the healing begins, one can feel a lump around the fracture site.  Later on, when the healing is complete, the bone smoothens out and the lump disappears.

Some babies can develop sternomastoid tumour without any evidence of injury during labour and delivery.  In this situation, it is suspected that the injury happened in the later part of pregnancy when the baby is filling up the space in the mother’s womb.  The head can be tilted because of the baby’s position, stretching the baby’s neck and injuring the sternomastoid muscle without anyone knowing it.

Whether the injury occur before or during delivery, the healing process is the same.  The muscle heals completely and the lump will disappear, although it does take a few months.

The only thing that you need to watch is whether you son develop tilting of his head.  Because of the injury and healing process, sometimes the sternomastoid muscle can become a little shorter on the injured side.  As a result, his head can be tilted to one side and rotated to the opposite side.  This problem can be corrected by stretching exercise that you can do at home, although you should see a physiotherapist who can show you how to do this exercise safely.

Of course there are other things that can cause a lump in a newborn baby’s neck.  Some are born with an enlarged thyroid gland; in this case the lump is called a goiter.  This is quite rare, but it can occur especially if the mother has certain kind of thyroid disease.  An ultrasound test will easily identify that as a goiter instead of the sternomastoid tumour.

Other cysts can also occur in some newborn baby’s neck.  The upper part of the windpipe is called the larynx.  The development of larynx and surrounding tissues in the foetus is fairly complex.  Once in a while, cysts can occur around the larynx because of minor mistakes in the development.  These cysts often show up when a child is older, and they are not cancerous.  Again, an ultrasound will show that they are cysts instead of swelling of the sternomastoid muscle.

I hope this explanation will reassure you that your son is perfectly safe.  You can keep an eye on his lump, and watch out for any tilting of his head.