X-ray signs of jaw cysts

X-ray diagnostics of jaw cysts

According to the International Histological Classification of Odontogenic Tumors, Jaw Cysts and Related Diseases (WHO, 1971), a distinction is made between jaw cysts that form as a result of developmental disorders and cysts of an inflammatory nature (radicular).

The group of cysts associated with developmental disorders includes odontogenic (primary cyst - keratocyst, tooth-containing - follicular cyst, gingival cyst and eruption cyst) and non-odontogenic (nasopalatine canal cyst and spherical-maxillary) fissure cysts and nasolabial cyst.

Follicular and radicular cysts predominate among cysts. They are formed on the upper jaw three times more often.

A tooth-containing (follicular) cyst is a developmental defect of the tooth-forming epithelium, occurring mainly in the second or third decade of life. A radiograph shows a single focus of tissue destruction of a round or oval shape, 2 cm or more in diameter, with clearly defined, sometimes wavy contours. The entire rudiment, the crown or part of it, sometimes two rudiments are immersed in the cyst cavity. The roots of teeth at different stages of formation may be outside the cyst. There is no tooth in the dental row, but a follicular cyst can also develop from the rudiment of a supernumerary tooth. An expansively growing cyst causes displacement of the rudiments of adjacent teeth. Thus, upward displacement of the rudiment of the third lower molar can serve as an indirect sign of the presence of a follicular cyst. Cysts cause pronounced deformation of the face due to swelling of the jaw, the cortical plates are displaced, thinned, but their destruction is rare.

Follicular cysts are usually painless, and their detection on an X-ray may be an accidental finding. Delayed tooth eruption is sometimes the only clinical sign that allows one to suspect pathology. Pain occurs when the cyst is infected and there is pressure on sensitive nerve endings. An exception is follicular cysts located in the area of primary molars, which are sometimes accompanied by pain, possibly caused by pressure from the cyst on the unprotected pulp of the resorbed root of the primary tooth.

Significant difficulties that arise in diagnosing follicular cysts of the upper jaw in children are due to the fact that the interpretation of the radiographic image is complicated by the rudiments of permanent teeth located above the milk teeth.

A radicular cyst, which is the final stage of cystogranuloma development, is formed as a result of the proliferation of metaplastic epithelium and the transformation of granulomatous tissue into a mucin-like substance. It can also form as a complication of endodontic procedures when pushing necrotic pulp into the periodontium periapically, especially during manipulations performed under anesthesia.

In children aged 7-12 years, radicular cysts most often develop in the area of the lower molars (2-3 times more often than in the upper jaw); in adults, the upper jaw is mainly affected in the frontal section.

The growth of the cyst occurs not so much due to the proliferation of the epithelium, but as a result of an increase in intracavitary pressure. An increase in the volume of the cyst is noted with resorption and restructuring of the surrounding bone tissue. The pressure inside the cyst fluctuates from 30 to 95 cm of water. Over the course of several years, the diameter of the cyst reaches 3-4 cm.

A radicular cyst is a cavity lined with a membrane and containing cholesterol-rich fluid. The outer layer of the membrane is dense fibrous connective tissue, the inner layer is multilayered flat nonkeratinizing epithelium.

On an X-ray, a cyst is defined as a focus of bone tissue destruction of a round or oval shape with clear, even, sometimes sclerotic contours. Unlike a granuloma, a radicular cyst is characterized by the presence of a sclerotic rim along the contour.

At the same time, it is impossible to reliably distinguish a radicular cyst from a granuloma based on X-ray data. When a secondary inflammatory process (suppurating cyst) is added, the clarity of the contours is disrupted, and fistulous tracts may appear.

The apex of the tooth root, usually affected by caries or treated for pulpitis or periodontitis, is immersed in the cyst cavity. As the cyst grows expansively, it causes displacement of the cortical plates; on the lower jaw, mainly in the buccal-lingual direction, on the upper jaw - in the palato-vestibular direction. Sometimes the cyst grows along the spongy layer of the lower jaw, without causing its deformation.

The direction of cyst growth is to a certain extent determined by the anatomical features of the lower jaw. With cysts located up to the third lower molars, deformation occurs predominantly in the buccal direction, since the cortical plate on this side is thinner than on the lingual side. When the cyst spreads beyond the third molar, swelling often occurs in the lingual direction, where the plate is thinner.

As a result of bone swelling, facial asymmetry occurs. Depending on the condition of the displaced cortical plate, a symptom of parchment crunch (with a sharp thinning of the plate) or fluctuation (with its interruption of the plate) is noted during palpation of this area. The cyst causes displacement and moving apart of the roots of adjacent teeth (divergence of roots and convergence of crowns). The position of the causative tooth usually does not change. With a defect in the dental arch in this area, the crowns fan out toward each other.

In patients with granulomas left after the extraction of the causative tooth, a residual (residual) cyst may develop. The cyst, located at the socket of the extracted tooth, usually has an elliptical shape, its diameter does not exceed 0.5 cm. Subsequently, the cyst causes deformation of the jaw and facial asymmetry. Residual cysts are more often formed on the upper jaw in men.

Due to the presence of signs of chronic inflammation in the walls of cysts located at the roots of the upper premolars and molars, they can cause a non-specific reaction of the adjacent mucous membrane of the maxillary sinus. The degree of expression of the reaction of the mucous membrane depends on the thickness of the bone layer between it and the pathological focus at the apex of the root.

Depending on the relationship between the cyst and the maxillary sinus, a distinction is made between adjacent, displacing and penetrating cysts.

In adjacent cysts, the unchanged cortical plate of the alveolar bay and the bone structure of the alveolar process are visible between the mucous membrane and the cyst. In displacing cysts, the cortical plate of the alveolar bay of the sinus is displaced upward, but its integrity is not violated. On the radiograph, penetrating cysts look like a hemispherical shadow with a clear upper contour against the background of the air of the maxillary sinus, the cortical plate of the alveolar bay is interrupted in places or is absent. Orthopantomograms, lateral panoramic radiographs and contact extraoral images in an oblique projection are of considerable help in determining the relationship between the cyst and the maxillary sinus.

Distinctive recognition of radicular cysts of the maxilla and retention cysts of the mucous membrane of the maxillary sinus is associated with certain difficulties. On zonograms and tomograms in the frontal-nasal projection, the cyst has the appearance of an oval, spherical shadow, sometimes narrowing toward the base, with a clear outline against the background of the air sinus. Retention cysts can increase in size, remain unchanged, or undergo regression.

To identify the relationship of radicular cysts with the floor of the nasal cavity, it is advisable to perform direct panoramic radiographs.

For large cysts of the upper jaw that grow into the soft tissues of the cheek, the most informative radiographs are those in oblique tangential projections.

Keratocyst occurs as a defect in the formation of the tooth germ and is characterized by keratinization of the multilayered keratinizing squamous epithelium lining the cavity. It is most often localized behind the third lower molars in the area of the angle and branch and tends to spread along the body and into the interalveolar septa, displacing the roots of the teeth, but not causing their resorption. The contours of the cavity are smooth, clear, sclerotic.

Sometimes developing near the forming follicle, the cyst is separated from it only by a connective tissue capsule and, according to the formal X-ray picture, resembles a follicular cyst. The final diagnosis is established only after histological examination. Relapses after surgery occur in 13-45% of cases.

The nasopalatine canal cyst is a fissure non-odontogenic cyst. The cyst develops from embryonic remnants of proliferating epithelium, sometimes preserved in the incisive canal. Radiographically, the cyst appears as a focus of bone rarefaction of a round or oval shape with smooth, clear contours. The cyst is located along the midline in the anterior sections of the hard palate above the roots of the central incisors. The closing cortical plates of the sockets and periodontal fissures are visible against the background of the cyst.