A sinus tract is an abnormal, narrow channel that develops beneath the skin or mucous membrane, representing a pathway for infection to drain from deeper tissues to the body’s surface. This tunnel forms as the body attempts to expel a persistent collection of infected material, such as an abscess. The presence of a sinus tract indicates a chronic, unresolved medical condition that requires professional attention. It is a type of wound complication that will not heal until the deep-seated cause is eliminated.
Defining the Sinus Tract
A sinus tract is a single, blind-ended passage with one opening, typically leading from an infected cavity to the outside of the body. This tunnel is not lined with healthy skin cells, but instead with highly vascular, fragile granulation tissue. Although granulation tissue is part of the body’s repair mechanism, its constant presence prevents the tract from closing and healing completely, allowing it to remain open and drain.
The tract originates from a collection of pus and necrotic debris, often deep beneath the skin or within an organ, which is under pressure. To relieve this pressure, the body creates this channel through the soft tissue as an escape route for the fluid. The opening, or stoma, on the skin’s surface periodically discharges pus or serosanguinous fluid (a mixture of blood and serum).
The internal path of the sinus tract can be tortuous or straight, following the path of least resistance through tissues. Its depth and direction depend entirely on the location of the source infection. Since the underlying infection remains, the tract cannot seal up, making it a sign of deep-seated, chronic inflammation that the immune system has failed to clear.
Common Causes and Locations
The formation of a sinus tract results from the body’s inability to fully resolve a localized, deep infection. One frequent example is an odontogenic sinus tract, which originates from a chronic periapical abscess at the root of a tooth. The resulting pus burrows through the jawbone to drain into the mouth or onto the skin of the face or neck. This drainage often relieves pressure, meaning the patient may not experience tooth pain, potentially leading to a misdiagnosis of a simple skin lesion.
Another common manifestation is the pilonidal sinus, which occurs in the cleft between the buttocks, near the tailbone. This condition starts when hair and debris become embedded in the skin, initiating an inflammatory response and subsequent infection. The resulting abscess burrows upward, creating a tract that drains onto the skin surface in the sacrococcygeal region. Skin abscesses that are not fully drained or that involve underlying bone, such as in chronic osteomyelitis, can also lead to a sinus tract.
In chronic skin conditions like Hidradenitis suppurativa, multiple sinus tracts can form in areas where skin rubs together, such as the armpits, groin, or under the breasts. These tracts represent deep, interconnected inflammation involving hair follicles and sweat glands.
Sinus Tract vs. Fistula
Sinus tracts and fistulae are frequently confused, but they describe two distinct anatomical phenomena. The defining difference lies in the number of openings and the types of tissue connected. A sinus tract is a blind-ended channel with only one external opening, connecting a focus of infection (a non-epithelialized cavity) to an epithelialized surface.
A fistula, conversely, is an abnormal communication that connects two separate epithelialized surfaces, meaning it has two distinct openings. It joins either two hollow organs together or joins an internal organ to the skin. Examples include passages between the bowel and the bladder, or an anal fistula connecting the rectum to the skin.
Understanding this distinction is significant for proper medical classification and treatment planning. While a sinus tract drains a single deep pocket of infection, a fistula allows the passage of contents, such as stool or urine, between two body cavities that should normally remain separate. In some instances, an untreated, long-standing sinus tract can erode into an adjacent structure, effectively transforming into a fistula.
Diagnosis and Treatment Approaches
Diagnosing a sinus tract begins with a physical examination and clinical history, focusing on the site of drainage and any associated symptoms. Healthcare providers often use probing, where a thin, flexible instrument is gently inserted into the tract opening to determine its depth and direction. Imaging studies are necessary to map the full extent of the tunnel and locate the source of the infection.
Specialized imaging techniques, such as magnetic resonance imaging (MRI) or computed tomography (CT) scans, provide detailed cross-sectional views of the underlying tissues. These scans accurately identify the deep abscess or foreign material maintaining the tract, especially when the source involves bone or dental issues. Contrast-enhanced imaging, called sinography, involves injecting a dye into the external opening to visualize the entire tract on an X-ray or CT scan, confirming the pathway and its origin.
Successful treatment requires eliminating the underlying cause of the infection, as antibiotics alone are often insufficient. For dental causes, non-surgical root canal therapy is typically performed to clear the infected pulp, allowing the tract to close spontaneously. When the cause is a chronic abscess or foreign body, the most common approach is surgical excision. This procedure removes the entire tract and the source of the infection. Surgical removal ensures the complete destruction of the abnormal pathway so that healthy tissue can heal the wound from the base up.