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What Is Pilomatrixoma in Children?

Medically Reviewed by Dan Brennan, MD on July 24, 2022

A pilomatrixoma is a lump that forms beneath the skin. This lump is a type of tumor that’s made from hardened, calcified hair follicle cells. Hair follicles make different kinds of hair all over your body. 

Pilomatrixoma tumors are almost always benign, which means that they’re not cancerous. They were originally described in the 1880s and have been studied ever since. 

Pilomatrixomas are most common in children under the age of 10. They often form on the head and neck but can occur anywhere on the body where hair grows. 

These tumors are sometimes called pilomatrixomas or calcifying epitheliomas of Malherbe.

What Causes a Pilomatrixoma?

Researchers don’t fully understand what causes a pilomatrixoma to form. One of the causes is likely genetic. The existence of these tumors tends to run in families. This means that the ability to form these tumors could be passed down from parents to children.

There’s some evidence that a mutation, or change, in a B-catenin gene is linked to the formation of pilomatrixomas. This gene helps with the creation of different types of cells in your hair follicles. The gene is called CTNNB1. 

A very small number of cases do have a definite cause. Approximately 3.9% of all cases studied so far are caused by external damage to the skin. This type of damage can be caused by: 

  • Trauma — particularly the kind that causes wounds to form on the skin
  • Insect bites
  • Surgery

Who Can Develop a Pilomatrixoma?

Pilomatrixomas are most common in children, though they occasionally occur in adults. The average age of onset is 4 1/2 years old. Around 90% of cases occur before the age of 10. 

Most of the remaining cases involve adults between the ages of 50 and 65 years old. For unknown reasons, people are more at risk for developing pilomatrixoma at these early and late stages in their lives. 

We need more research to understand exactly how common these tumors are. Data suggests that pilomatrixomas make up between 0.001% and 0.0031% of all dermatological — or skin-related — samples that physicians examine. 

How Is a Pilomatrixoma Diagnosed?

Your doctor will need to physically examine the lump in your child’s skin in order to make an accurate diagnosis. They’ll also ask questions about your family medical history. 

The symptoms of a pilomatrixoma can resemble other skin conditions, including serious cancers. Your doctor needs to do enough tests to make sure that they’ve accurately identified your child’s condition. 

In many cases, your doctor will need to perform a biopsy to obtain this accurate diagnosis. A biopsy is a small sample of tissue taken from the lump. This sample is removed either with a special needle or with surgery. 

Your doctor can look at this sample under a microscope. This will help them determine whether or not the cells are cancerous or otherwise abnormal.

In some cases, the doctor may also order imaging tests to look at the lump. Imaging tests could include: 

What Are the Symptoms of a Pilomatrixoma?

The symptoms of a pilomatrixoma can vary from person to person. The main noticeable symptom of a pilomatrixoma is the hard, calcified lump under your child’s skin. 

Pilomatrixomas tend to be rather slow-growing. Over time, you’ll be able to feel the lump with your finger. They rarely get larger than 3 centimeters in diameter.

These lumps normally occur one at a time. But your child could have multiple lumps at the same time. 

In 70% of cases, these lumps form on your child’s head and neck. The most common region is right in front of the upper ear. They may also form on your child’s face and arms. There are even rare instances of pilomatrixomas forming on the scrotum and vulva. These are all regions that have hair follicles. 

The skin that covers the lump may or may not be affected. If your child has a pilomatrixoma, the skin that covers it could be: 

  • Completely normal
  • Hard or firm to the touch
  • Reddish in color
  • Bluish in color

A pilomatrixoma is usually painless, but, in rare instances, ulcers can form on the surface. These are open wounds that leave your child at risk of developing an infection. Infections can be painful. 

Some people report mild sensations of pain and itchiness even when the skin around the pilomatrixoma hasn’t opened up. 

What Is a Pilomatrixoma Carcinoma?

In very rare instances, pilomatrixomas can become malignant, or cancerous. This has only happened in 125 reported cases of pilomatrixomas so far. These incidences are formally called pilomatrix carcinomas.  

Pilomatrix carcinomas are more common in adults than children. In fact, there’s only one reported case of a malignant pilomatrixoma forming in a child. This cancerous form is more common in males than females. 

How Is a Pilomatrixoma Treated?

The main way to treat a pilomatrixoma is to remove it. Pilomatrixoma removal is a fairly simple surgical procedure. It involves taking out all of the tissue in the lump and some of the surrounding tissues. 

The exact amount of tissue removed will vary from person to person. Your surgeon may also remove tissue from a different part of your body and use it to cover the area where your child’s pilomatrixoma formed. This is only necessary when the exposed region is large. 

Since most cases of pilomatrixomas aren’t particularly dangerous or problematic, surgery isn’t always necessary. It’s ultimately the parents’ decision. Factors to consider include: 

  • Your child’s age
  • The size of the tumor
  • Your child’s ability to tolerate surgeries and the medications required for surgery

Treatment is similar even in those rare cases where the pilomatrixoma is cancerous. The tumor and surrounding tissues are removed in surgery. Additional treatment steps are only required if the tumor comes back or if the cancer spreads to other parts of your body. Further treatment could include chemotherapy or radiation sessions. 

What Is the Prognosis for Someone With a Pilomatrixoma?

In most instances, people with pilomatrixomas recover without any additional complications. But keep in mind that pilomatrixomas can re-form even after they’ve been removed. They may appear in a new location on your child’s body. 

When Should You Contact Your Doctor?

You should schedule an appointment with your doctor whenever you notice a lump or rash on your child’s skin. In some cases, these symptoms can be signs of a serious condition like cancer. The sooner you get your child checked out, the sooner your doctor can begin to diagnose and treat their condition. 

Show Sources

SOURCES: 

Children’s National: “Pediatric Pilomatrixoma.” 

Le, C., Bedocs, P.M. StatPearls, “Calcifying Epithelioma of Malherbe.”  

Stanford Children’s Health: “Pilomatrixoma in Children.” 

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