What is ameloblastoma?
Ameloblastoma is a non-cancerous type of bone tumour. Ameloblastoma is called an odontogenic tumour because it starts from cells normally involved in the development of the teeth (“odonto” means “teeth” and “genic” means “producing”). These tumours tend to grow slowly over time. Large tumours can cause pain, swelling, loose teeth, and facial deformity.
Where does ameloblastoma start?
Most ameloblastomas start in the jaw. The jaw is made up of two bones, the mandible (lower jaw) and the maxilla (upper jaw). The bones of the jaw are different from other bones in the body because create and support teeth. Human teeth develop within the mandible and maxilla before birth (in utero) although they do not become visible for months or even years after birth. Each tooth develops from a structure called the tooth bud. Within the tooth bud are specialized cells called ameloblasts which produce enamel, a hard substance that gives teeth their strength. Ameloblastoma starts from ameloblasts that remain in the jaw after birth.
How do pathologists make this diagnosis?
The diagnosis of ameloblastoma is usually made after the entire tumour is removed and sent to a pathologist to examine under a microscope. Sometimes the diagnosis will be made after only a small piece of the tumour is removed in a procedure called a biopsy.
Types of ameloblastoma
Pathologists divide ameloblastoma into different groups called types or variants based on how the tumour looks when examined under the microscope. All types of ameloblastoma are non-cancerous tumours that are unlikely to grow back if fully removed.
- Follicular type: This is the most common type of ameloblastoma. It is made up of large groups of tumour cells that look similar to the ameloblasts in the developing tooth. The tumour cells at the edge or periphery of the groups tend to line up side-by-side in a pattern that pathologists describe as palisading. The nucleus of the cell may also be located in an unusual location away from the bottom of the cell. These cells are described as having ‘reverse polarity’ because the normal location of the nucleus or ‘normal polarity’ is near the bottom of the cell. Finally, the cells in the centre of the group are long and thin and surrounded by loose connective tissue. These cells look similar to cells called the stellate reticulum which are normally found in the developing tooth.
- Plexiform type: This is the second most common type of ameloblastoma. The tumour cells in this type of ameloblastoma look similar to ameloblasts in the developing tooth and are connected together to form long chains of cells. The chains of cells typically connect together in a pattern pathologists describe as ‘anastomosing’.
- Desmoplastic type: This is a rare type of ameloblastoma. Compared to the follicular and plexiform types, the tumour cells in the desmoplastic type of ameloblastoma look less similar to the ameloblasts in the developing tooth. The tumour cells are often found in groups and the cells at the edge of the group are square-shaped or flat. The tumour cells in the centre of the group are long and thin and surrounded by loose connective tissue. These cells look similar to cells called the stellate reticulum which are normally found in the developing tooth. The groups of tumour cells are surrounded by dark pink connective tissue. Pathologists describe this connective tissue as fibrotic or hyalinized.
- Acanthomatous type: This is a rare type of ameloblastoma. The tumour cells in this type of ameloblastoma are larger and pinker than the tumour cells in the other types of ameloblastoma and they look similar to specialized squamous cells that are normally found in other areas of the body such as the skin.
by Jason Wasserman MD PhD FRCPC (updated October 8, 2021)