Also known as Stensen's duct, the parotid duct is a tubular structure located inside the parotid salivary gland. The duct takes saliva from the parotid gland into the mouth at the level of the upper molars. Since the parotid duct lies close to the surface of the face, it may be harmed during facial surgery or due to accidental injury. Sometimes what is called a salivary stone may form and block the duct, requiring removal by keyhole surgery.
Saliva is necessary for moistening and cleaning the mouth and enabling swallowing to occur. When a person is speaking, saliva helps the tongue move freely. It also has antacid and antibacterial properties, and contains enzymes that digest starch and fat.
There are three pairs of salivary glands in all. The submandibular glands lie beneath the floor of the mouth, and the sublingual glands, which produce the most saliva, are under the tongue. Situated in the cheeks, just before and slightly below the ears, are the parotid glands. They are the largest type of salivary gland. Many tiny salivary glands also exist scattered in and about the oral cavity.
The parotid duct is around 2 inches (about 5 cm) in length. Cells inside the parotid gland produce saliva, which then drains through smaller ducts into the main parotid duct. The parotid gland makes about 20 percent of total saliva, and it is quite watery compared with the secretions of the other salivary glands. After its emergence from the gland, the parotid duct runs forward across the masseter muscle of the cheek. In some people a tiny accessory parotid gland is found here which also drains into the duct.
Just before the parotid duct opens into the oral cavity it passes between the mouth lining and one of the cheek muscles known as the buccinator muscle. The two surrounding layers act as a valve and protect the duct from inflating when a person blows air out forcefully. This mechanism proves particularly useful for people who blow glass or play brass and woodwind instruments.
Occasionally, blockage of the parotid duct can occur. This typically happens when a salivary stone becomes lodged within the duct, causing a blockage of saliva. The gland usually swells and feels painful, especially around meal times, and infection may follow. Sometimes stones may pass out of the duct by themselves, and massaging the gland, together with antibiotics and pain relief, may be all that is required. Otherwise, treatment involves removal of the stone using keyhole surgery after any associated infection has been resolved.