This article will help you read and understand your pathology report for dermatofibroma.
by Glenda Wright MBBCh and Allison Osmond MD FRCPC, reviewed on May 8, 2019
The anatomy of skin
Skin is made up of three layers: epidermis, dermis, and subcutaneous fat. The surface and the part you can see when you look at your skin is called the epidermis. The cells that make up the epidermis include squamous cells, basal cells, melanocytes, Merkel cells, and cells of the immune system. The squamous cells in the epidermis produce a material called keratin which makes the skin waterproof and strong and protects us from toxins and injuries.
The dermis is directly below the epidermis. The dermis is separated from the epidermis by a thin layer of tissue called the basement membrane. The dermis contains blood vessels and nerves. Below the dermis is a layer of fat called subcutaneous adipose tissue.
Many different types of cells are normally found in the dermis including fibroblasts and histiocytes. Fibroblasts produce the collagen and other substances that make the dermis strong. Histiocytes are a type of immune cell that protect the body from any infections or toxins that enter through the skin.
What is a dermatofibroma?
A dermatofibroma is a very common type of non-cancerous skin tumour. They grow slowly, have a pink to brown colour, and are usually small and painless. Another name for a dermatofibroma is benign fibrous histiocytoma.
Under the microscope, dermatofibromas are made up of long thin cells that pathologists call spindle cells. These spindle cells look very similar to the fibroblasts and histiocytic cells normally found in the dermis. Giant cells, which are histiocytes that have joined together to form one large cell, are also seen.
The border between a dermatofibroma and the surrounding normal skin can be very hard to see. For this reason, it can be hard for your doctor to remove the entire tumour and a small number of tumours may come back (local recurrence) after they are removed.
Types of dermatofibroma
There are different types of dermatofibromas based on how the tumour looks under the microscope. Pathologists call these tumours variants and like classic dermatofibromas, they are all non-cancerous.
Common variants of dermatofibroma include:
How do pathologists make this diagnosis?
The diagnosis of dermatofibroma is usually made after the entire tumour has been surgically removed and sent to a pathologist for microscope examination. Sometimes, your doctor will remove a small piece of the tumour in a procedure called a biopsy before removing the entire tumour.
It can be very challenging for a pathologist to make the diagnosis of dermatofibroma after only examining a small piece of the tumour because there are other types of tumours that can look very similar to dermatofibroma. In this case your pathologist may offer a list of possible diagnoses which includes dermatofibroma. A final diagnosis will be given after the entire tumour is removed and examined.