Dysplasia is a term that refers to abnormal tissue development and can describe a number of different conditions. Squamous dysplasia, however, refers to abnormalities in squamous epithelium, the epithelium being the layer of cells that lines a cavity or surface in the body, like the cervical epithelium or esophageal epithelium for example. Squamous cell dysplasia is not necessarily cancerous although it can be a precursor to certain kinds of cancer.
Epithelial cells are cells lining a cavity or outer surface of the body. Epithelium can be classified by their structure and the shape of the cells that compose them; columnar epithelium, for instance, is made up of cells that are more or less cylindrical or column-shaped, while unilaminar describes epithelium that are a single cell thick. Squamous epithelium is composed of flattened cells shaped like scales. It can be simple, meaning that it's unilaminar, or stratified, in which case it's composed of multiple layers of cells. The outer layer of your skin is stratified squamous epithelium, while the lining of the alveoli or air sacs in your lungs is simple squamous epithelium.
Dysplasia is a broad term that covers abnormal tissue development--and hence a number of developmental abnormalities. Dysplasia of squamous epithelia, however, describes abnormalities in cells from squamous epithelium--like the cervical epithelium. The portion of the cervix that extends into the vagina is lined with stratified squamous epithelium, while the uterine cervix or endocervix is lined with simple columnar epithelium.
Tissue samples that exhibit abnormal features when examined under the microscope are dysplasias. The cells may appear disorganized like soldiers breaking ranks; the cell size and shape may be unusual and the cell nuclei may appear abnormal. The Pap test is a common diagnostic procedure that checks for cervical dysplasia. Endoscopy can help identify squamous dysplasia in the esophagus, among other conditions.
Dysplasia doesn't necessarily mean you have cancer, but it can be a precursor to cancer. Dysplasia of stratified squamous epithelium is generally graded as mild, moderate or severe dysplasia, where severe dysplasia means the abnormal cells extend all the way through the epithelium. If your doctor finds you have squamous epithelial dysplasia--like esophageal dysplasia or cervical dysplasia--she may order further tests or schedule follow-ups to monitor any changes.
Squamous dysplasia is the earliest stage in the progression towards squamous cell carcinoma; it doesn't necessarily mean, however, that you have or will develop cancer. The risk that mild dysplasia will become cancerous is low, and mild dysplasia will often resolve itself without further intervention. High-grade or severe dysplasia, on the other hand, is a somewhat more ominous sign and is sometimes referred to as carcinoma in situ (CIS), a condition where abnormal cells divide without invading other tissues; the risk that a CIS will progress further to become cancer is fairly high.