Lymphoepithelial cysts (LECs) are uncommon, non-cancerous lesions defined by their unique composition of both lymphatic tissue and epithelial cells. They are fluid-filled sacs that develop in soft tissues containing these two components. The epithelial layer forms the wall of the cyst, which is then surrounded by a dense collection of immune cells called lymphoid tissue. This combination of tissue types gives the lesion its specific name. LECs are generally slow-growing and rare.
Common Locations and Physical Characteristics
The most frequent site for a lymphoepithelial cyst is within the salivary glands, particularly the parotid gland located near the ear. The parotid gland naturally contains lymph nodes, making it a susceptible location for the formation of these cysts. When LECs occur here, they typically present as a painless swelling that develops gradually over time.
The oral cavity is another common area for LECs, specifically in the soft tissues of the floor of the mouth or the lateral border of the tongue. In the mouth, they often appear as well-defined raised nodules or papules that may have a yellowish or whitish color due to the keratinous debris and fluid inside. These cysts are usually soft, movable masses that rarely cause pain unless they become infected.
Less frequently, LECs can be found in distant sites like the pancreas. Pancreatic LECs are extremely rare and often discovered incidentally during imaging performed for other reasons. Regardless of the location, LECs are typically unilocular or multilocular, meaning they consist of one or multiple fluid-filled chambers.
Understanding the Causes of Formation
The exact mechanism of LEC formation is not fully understood, but two primary theories attempt to explain their development. The first theory suggests a developmental or embryological origin, proposing that the cysts arise from epithelial tissue remnants trapped within lymph nodes during embryonic development. These trapped cells can later undergo cystic change, leading to the formation of an LEC.
The second theory suggests that LECs form through reactive hyperplasia, often in response to inflammation or infection. In this scenario, the ducts of a salivary gland become obstructed, possibly due to a localized overgrowth of surrounding lymphoid tissue. This blockage causes the duct to dilate and swell, eventually forming a cyst lined by epithelial cells and surrounded by reactive immune tissue.
Association with HIV
A clinical association exists between lymphoepithelial cysts, particularly those in the parotid gland, and human immunodeficiency virus (HIV) infection. For individuals with HIV, the presence of LECs in the parotid gland is considered a localized manifestation of persistent generalized lymphadenopathy, where the body’s immune system is chronically stimulated. The HIV virus can lead to lymphoid hyperplasia, causing the trapped lymphoid tissue within the parotid gland to swell and obstruct the salivary ducts, resulting in cyst formation.
The vast majority of LECs in the general population occur sporadically and are not related to HIV status. However, due to this known association, a patient presenting with an LEC, especially a cystic parotid swelling that is often bilateral or multicystic, may be advised to undergo HIV serology testing. Treatment of the underlying HIV infection with antiretroviral therapy can sometimes lead to the resolution or reduction in size of these cysts.
Diagnosis and Management
Diagnosis
The process of diagnosing a lymphoepithelial cyst begins with a thorough physical examination where the physician assesses the size, consistency, and mobility of the mass. Imaging studies such as Ultrasound, Computed Tomography (CT), or Magnetic Resonance Imaging (MRI) are often used to characterize the lesion. Imaging helps determine if the mass is purely fluid-filled or contains solid components, its size, and its exact relationship to surrounding anatomical structures.
The definitive diagnosis of an LEC typically requires a tissue sample examined under a microscope. Fine Needle Aspiration (FNA) is commonly performed, especially for lesions in the head and neck. During FNA, a thin needle extracts fluid and cells, which a pathologist analyzes for the characteristic presence of epithelial cells and mature lymphocytes. For pancreatic lesions, Endoscopic Ultrasound-Guided FNA (EUS-FNA) helps distinguish the benign cyst from a potentially more serious cystic neoplasm.
Management
Management of LECs is guided by their benign nature and the presence of symptoms. If the cyst is small, asymptomatic, and the diagnosis is confidently established, a conservative approach of observation and monitoring may be chosen. This involves periodic check-ups to track any changes in size or symptoms.
Surgical excision is the most common and often curative treatment option. Surgery is recommended for cysts that are large, symptomatic, or when the diagnosis needs confirmation to rule out other conditions. Excision removes the entire lesion and provides a definitive resolution with a low risk of recurrence. Less common non-surgical treatments include repeated aspiration to drain the fluid, or sclerotherapy, which involves injecting a substance into the cyst to promote scarring.