The term “pannus” refers to an abnormal layer of tissue or growth that develops over a normal structure, often in response to chronic inflammation or physical excess. This tissue is typically composed of fibrovascular or granulation material. The word itself comes from the Latin term for “cloth” or “rag,” which describes the sheet-like nature of the growth. While the name is the same, the appearance and composition of pannus are vastly different depending on where in the body it forms.
Appearance in Joints (Rheumatoid Pannus)
Rheumatoid pannus is an aggressive, destructive inflammatory tissue that develops within the joints of individuals with conditions like Rheumatoid Arthritis. This growth forms when the synovium, the membrane lining the joint capsule, becomes hyperactive and thickens significantly. The pannus appears as a rough, irregular mass of tissue growing inward from the edges of the joint space.
The proliferative nature of this tissue is fueled by new blood vessels (neoangiogenesis), giving it a highly vascular appearance that may be reddish-brown or pink in color. This abnormal layer consists of a dense collection of inflammatory cells, including macrophages and lymphocytes, which release tissue-destroying enzymes. The pannus actively invades and grows over the smooth cartilage surfaces and into the adjacent bone.
This internal growth causes the erosion of bone and cartilage, leading to the characteristic joint damage seen in the disease. The surface of the pannus is often irregular due to the formation of small, hair-like growths called villi. This invasive mass fills the joint space, impeding normal movement and contributing to swelling and pain.
Appearance in the Eye (Corneal Pannus)
Corneal pannus is the visual result of new blood vessel growth and associated fibrous tissue extending onto the cornea, the clear front surface of the eye. The healthy cornea is normally avascular, meaning it contains no blood vessels, so the appearance of any vessels indicates an abnormal process, typically caused by chronic irritation or oxygen deprivation. This growth usually originates at the limbus, the boundary between the cornea and the white sclera, and then creeps inward.
The pannus appears as a cloudy, hazy area on the peripheral cornea, compromising the tissue’s transparency. Fine, reddish lines are visible within this cloudy area, representing the new blood vessels that have invaded the clear tissue. The extent of the growth is categorized by how far it has moved toward the center of the cornea.
A small growth, known as a micropannus, extends less than two millimeters into the cornea, while a macropannus covers a larger area. The visual impact depends on the density of the growth and how close it comes to the central visual axis. If the inflammatory process has subsided, the blood vessels may appear as “ghost vessels,” which are fine, clear lines representing the scarred, non-perfused remnants of the old vessels.
Appearance of Excess Skin and Fat (Abdominal Panniculus)
The abdominal panniculus, often referred to simply as a pannus, is a large, apron-like fold composed of excess skin and subcutaneous fat hanging from the lower abdomen. This excess tissue typically hangs down over the pubic region, limiting mobility and causing hygiene issues. The skin underneath the fold is subject to moisture and friction, leading to irritation, redness, and potential skin breakdown.
The visual severity of the abdominal panniculus is graded on a five-point scale based on how far the fold descends over the body. The grades are defined as follows:
- Grade 1: The fold hangs down to cover the pubic hairline and mons pubis.
- Grade 2: The pannus extends further down to cover the genitals and the upper thigh crease.
- Grade 3: The fold reaches the upper third of the thighs, creating a pronounced overhang.
- Grade 4: The fold extends down to the mid-thigh level, significantly affecting posture and ambulation.
- Grade 5: This is the most severe form, extending to the knees or further down the legs.