Striated duct adenoma

by Jason Wasserman MD PhD FRCPC
December 5, 2024

Striated duct adenoma is a rare, benign tumour that develops in the salivary glands, most often in the parotid gland, situated in front of and below the ears. The tumour is made up of small ducts (tiny tube-like structures) similar to those normally found in the salivary glands. These tumours are typically slow-growing and do not spread to other parts of the body.

What are the symptoms of striated duct adenoma?

Striated duct adenomas often cause a painless lump or swelling in the affected salivary gland. Some people may experience mild discomfort or tenderness in the area, but these symptoms are uncommon. Many cases are found during routine examinations or imaging studies for other conditions.

What causes a striated duct adenoma?

The exact cause of striated duct adenoma is not well understood. It is thought to develop from abnormal growth of the ducts within the salivary glands. There are no known risk factors or associations with specific lifestyle or environmental factors.

How is this diagnosis made?

The diagnosis of striated duct adenoma is made after a biopsy or surgical removal of the tumour. A pathologist examines the tissue under a microscope to confirm the diagnosis and rule out other types of salivary gland tumours. Additional tests, such as immunohistochemistry, may also be performed to support the diagnosis.

What are the microscopic features of striated duct adenoma?

Under the microscope, striated duct adenomas are well-defined and surrounded by a capsule. They comprise small, closely packed ducts with very little stroma (connective tissue) between them. Small cysts, or fluid-filled spaces, may also be seen. Some tumours contain many blood vessels, including those with a branching “staghorn” appearance.

The ducts in striated duct adenoma are lined by a single layer of columnar cells, which are tall, rectangular cells with pink (eosinophilic) cytoplasm. This feature distinguishes them from lesions of the intercalated ducts, another type of salivary gland duct. Occasionally, the spaces inside the ducts (lumens) may contain pink material that looks like colloid and red blood cells.

In some cases, areas of hyalinization (scarring) may make the tumour look similar to an oncocytoma, another type of salivary gland tumour. Rarely, the surrounding salivary gland tissue may show increased size and number of striated ducts (called striated duct hyperplasia). Fat cells may also be present in small or large amounts within the tumour.

Immunohistochemistry

Immunohistochemistry is a special test that uses antibodies to detect specific proteins in tumour cells. This test helps pathologists confirm the diagnosis of striated duct adenoma. The tumour cells in striated duct adenoma are strongly positive for keratin proteins, particularly CK7 and CK5/6, commonly found in salivary gland duct cells.

The tumour cells also show strong staining for a protein called S100, which is present in both the nucleus and the cytoplasm. This is an important feature that helps differentiate striated duct adenoma from oncocytoma, another type of salivary gland tumour.

Proteins that are normally found in the outer (abluminal) layer of ducts, such as calponin, SMA, SMMHC, and p63, are present only in isolated cells within the tumour and do not form a continuous layer. This indicates that the tumour does not have a true basal or myoepithelial layer, which is another distinguishing feature.

Markers that indicate thyroid tissue, such as thyroid transcription factor 1 (TTF1) and thyroglobulin, are negative in striated duct adenoma. This helps rule out tumours that originate from thyroid tissue.

Does a striated duct adenoma need to be removed?

In most cases, striated duct adenomas are removed through surgery. Although this tumour is noncancerous and does not spread to other parts of the body, removal is recommended to confirm the diagnosis and rule out other types of salivary gland tumours that may appear similar. Surgery also eliminates the possibility of the tumour growing larger and causing discomfort or affecting nearby structures.

After removal, striated duct adenomas do not typically come back (recur), and no further treatment is usually necessary. If you have concerns about surgery or the need for removal, your doctor can explain the reasons for this recommendation based on your specific situation.