In learning to make a differential diagnosis of soft tissue pathosis, the first step is to recognize the presence of an abnormal change, either in function or structure, during a clinical oral examination. In this series of presentations, we will only be concerned with structural changes. Click on any link to see a picture of what is being described.

In order to properly record or chart an abnormal finding, a common understanding of the morphology or oral lesions must be achieved.

All lesions of the oral cavity can be placed in one of three broad morphologic categories:

  1. Elevated
  2. Depressed
  3. Flat

Elevated, Depressed and Flat lesions can exist in specific basic forms which are referred to frequently in texts and literature.

As you encounter various oral lesions, you should be able to answer questions such as:

Is the lesion elevated, depressed or flat?

Is it generalized or localized?

Is it single or multiple?

Is it fluid filled or not?

What is the character of the fluid, if present?

What is the approximate size (use millimeters and centimeters) of the lesion?

Is it larger at the base or on the top?

If multiple lesions are present, are they separate or coalescing?

In fact, the way you will know whether or not you have learned this material is when you encounter an oral lesion, do questions like these automatically come up in your mind.

Elevated lesions

  • An elevated lesion is one in which the surface is above the normal plane of the mucosa.
  • All elevated lesions are not necessarily symmetrical but may have irregular contours.
  • Clinically, it is quite easy to determine that a lesion is elevated by looking at the lesion at different angles and relying on stereoscopic vision.
  • Perspective is helpful since an elevated lesion may hide or cover any normal structures.

Elevated lesions may be localized or generalized.

  • localized elevated lesion is limited to a small, focal area.
  • generalized elevated lesion involves most or all of an area or site. Some generalized lesions may involve more than one site.
  • It is usually easier to determine the limits of involvement of localized lesions than of generalizedlesions.
  • Localized lesions may be single or multipleThe number of lesions are often characteristic for a particular disease. A single lesion is one lesion of a particular morphology. Where more than one lesion of a particular morphology is present, they are considered as multiple lesions.

Elevated lesions may be further divided into blisterform or non-blisterform lesions.

Blisterform lesions are those which contain a body fluid, usually identified by their characteristic translucent appearanceTactile examination of a blisterform lesion will reveal asoft rebounding sensation. Blisterform lesions are given descriptive names, depending on their size and the material contained within the blister. A blisterform lesion is either avesicle, pustule, or bulla.

vesicle is a blisterform lesion which is less than 5 mm in its greatest diameter and contains serum ormucin. The serum or mucin gives the vesicle a clear or translucent, slightly white appearance. Vesicles in the oral cavity are often collapsed due to trauma, creating a collapsed vesicle which appears white or cream colored.

pustule is a blisterform lesion that contains pus which imparts a yellowish coloration. It may be greater or less than 5 mm.

bulla is a blisterform lesion larger than 5 mm in its greatest diameter which may contain serum or mucin. It may occasionally contain extravasated blood. The color may appear clear, red or blue, depending upon the fluid content. Similar to vesicles, bullae often collapse due to trauma in the oral cavity and are termedcollapsed bullae which are white or red in color.

Non-blisterform lesions are solid and contain no fluid. They are recognized by their opaque appearanceOn palpation, they feel firm and solid. Non-blisterform lesions are also given descriptive names, depending on their size and pattern. A non-blisterform lesion is either apapule, nodule, tumor or plaque.

papule is a lesion which consists of tissue and is less than 5 mm in its greatest diameter.

nodule is similar to a papule in that it consists of tissue, but it is greater than 5 mm and less than 2 cmin its greatest diameter.

tumor is similar to a nodule in that it consists of tissue, but it is greater than 2 cm in its greatest diameter.

plaque is a slightly raised non-blisterform lesion which has a broad flat top like a plateauIt has a "pasted on" or "stuck on" appearance and is usually greater than 5 mm in diameterThe elevation and density of plaques vary. When the plaque is not as obviously raised above the plane of the normal mucosa, or not as dense, it will be more difficult to interpret as a "plaque".

papule, nodule, and tumor may be classified as sessile or pedunculated according to their base or attachment to the mucosa.

sessile lesion is a papule, nodule, or tumor whose base or attachment to the normal mucosa is the greatest diameter of the lesion.

pedunculated lesion is a papule, nodule, or tumor that has an attachment to the normal oral mucosa which is smaller than the greatest diameter of the lesion. In other words, the lesion is attached by a stalk or pedicle.

The size of a lesion is often a clue to its diagnosis. It is not necessary to measure exactly the size of a lesion. Only a reasonably accurate estimate of the lesion's size is expected. Size of lesions is best estimated by comparing the lesion with familiar landmarks of known size immediately adjacent to it. These landmarks include teeth, parotid papillae, lingual papillae, incisive papillae, etc.

For example, lower incisor teeth are approximately 5 mm in their greatest width and upper central incisors, 8-9 mm in their greatest width. Molars are approximately 10 mm or 1 cm in their mesiodistal aspect. The lingual filiform and fungiform papillae are less than 1 mm in diameter.


You will recall that more than one lesion of a particular morphology is considered multiple. Multiple lesions with any of the morphologic characteristics so far described can be separate or coalescing.However, in the oral cavity, small lesions coalesce more frequently than large ones.

Separate lesions are usually few in number and relatively widely spaced, but not always. They usually remain individual, distinct lesions, even if they tend to enlarge after their initial appearance.

Coalescing lesions are numerous and in proximity to one another. Their margins may merge and leave a single lesion, even if they enlarge only slightly after their initial appearance.

With multiple lesions that vary in size, the morphology of peripheral lesions becomes important in deciding whether the lesions should be classified as separate or coalescing.

Whenever both separate and coalescing lesions are present, the predominant type of lesion determines the correct morphologic classification. If neither separate nor coalescing lesions is predominant, it may be described as either.


Depressed lesions

depressed lesion is one in which the surface is below the normal plane of the mucosa.

  • Most depressed lesions are ulcers. An ulcer is a loss in continuity of the oral epithelium. Clinically, the center of the ulcer is often yellow to grey with a red periphery. Occasionally, a red center may be observed. Ulcers often result from the rupture of elevated lesions such as vesicle, bullae, pustules, and papules.
  • Some depressed lesions are the result of atrophy or scarring and have an intact epithelial surface.
  • Other depressed lesions pits or blind "pouches" caused by a failure of complete filling out during embryologic development.
  • Clinically, it is quite easy to determine if a lesion is depressed by looking at the lesion from different angles and relying on stereoscopic vision.
  • Depressed lesions may be single or multiple.


single depressed lesion is one lesion of a particular morphology. Where more than one lesion of a particular morphology is present, they are multiple. Since descriptors of single and multiple lesions vary slightly, single lesions will be considered first.

Single depressed lesions


  • regular - if the border is a continuous linear outline and resembles a circle or an oval.
  • irregular - if the border has numerous deviations from a circular or oval pattern


  • Raised - margin is above the plane of the normal mucosa.
  • Smooth - margin is on the same plane as the normal mucosa.

Depth - distance from the base of the ulcer to the plane of margin

  • superficial - less than 3 mm in depth.
  • deep - greater than 3 mm in depth.

Multiple depressed lesions

Multiple depressed lesions have the same morphologic descriptors as discussed for single lesions: Outline, margin, depth, and diameter.In addition, multiple lesions may be either separate or coalescing.

  • Separate lesions - few in number or widely spaced, not likely to merge or blend into one another, even if they enlarge. They remain distinct.
  • Coalescing lesions - numerous and in proximity, may merge or blend into one another after minor enlargement. When this occurs, a single lesion is formed. The original outline of the initial lesions may or may not still be detectable.
  • If both separate and coalescing lesions are present, the predominant type of lesion determines the correct morphologic classification. In this case, the lesions are best described as coalescing. If neither separate nor coalescing lesions are predominant, it may be described as either.


Flat lesions

A flat lesion is one in which the surface is on the same plane as the normal oral mucosa. Because of this, any lesion of normal mucosal coloring would be undetectable (except on the dorsum of the tongue). Therefore, the only way most flat lesions can be detected is through a change in color.

A flat lesion with an abnormal color is called a macule. Although color is a primary characteristic of macules, color will be the subject of another unit.

Since the tongue is anatomically unique, special considerations must be given to flat lesions occurring on the dorsal and lateral borders of the tongue.

Loss of papillae results in an apparent depressed lesion, but since the mucosal surface is intact, it is in fact a flat lesion. Since it does not involve an abnormality of color, however, it is not a macule. What you have to understand is that lesions of the tongue that involve loss of papillae are exceptions, the only flat lesions that are not macules.

Lesions resulting from a loss of papillae may be single or multiple.

  • Single and multiple lesions may be regular or irregular in outline.
  • Multiple lesions are often irregular.