Cysts are tumor-like structures of developmental or inflammatory origin. As this kind of growth does not originate in cell proliferation, it is not considered a tumor. Structurally, a cyst is a mostly liquid-filled pouch with endothelial lining and connective tissue wall. They are found both in bones and soft tissues.
Bone cysts can be odontogenic cysts, non-odontogenic cysts and pseudocysts (bone cavities without endothelial lining).
ODONTOGENIC CYSTS
Their cavity is mostly filled by hay-yellow, thin, serous liquid, and it is not rare that this liquid contains cholesterol crystals visible to the naked eye. The liquid exerts hydrostatic pressure on the surrounding bone, by which the bone gradually grows thin. Odontogenic cysts are made up of stratified squamous epithelium, but the differentiation between the various types is possible only by histology. The cyst is constantly growing, and it can push the roots of neighboring teeth apart, which makes their crowns tilt toward each other. Such a finding, even at the routine examination, must always raise the possibility of a cyst.
Cysts are usually symptom-free, and they are discovered as a by-finding in an X-ray done for some other reason.
Exceptions are when the crowns are visibly dislocated, the cyst is superinfected, or when the bone protrudes because of the cyst.
Odontogenic, non-inflammatory cysts
Odontogenic, non-inflammatory cysts include perinatal cysts, gingival cysts of adults, primordial cysts, eruption cysts, lateral periodontal cysts and follicular cysts.
Follicular cysts
Of these, follicular cysts are the most frequently encountered. According to the most widely accepted explanation, this cyst is the product of the enamel epithelium remaining after the crown of an unerupted tooth has developed. The typical predilection site is around the crown of the unerupted tooth, in the majority of cases a lower wisdom tooth or a canine.
PATHOLOGY
In X-ray images, a round shadow with marked edge is seen around the crown of the impacted tooth. (If the width of the osteolysis is less than 2mm around the crown, it is possibly a normal folliculus.) These cysts are unilobular, but rarely can they be multilobular.
Its treatment consists of the surgical removal of the impacted tooth together with the cyst. Re-occurrence raises the possibility of a keratocyst.
Keratocysts
A keratocyst may not be diagnosed without histology. Random histological examination of jaw cysts found 5–
10% to be of this kind. These are formed from the remnants of the dental laminae or the epithelium of the enamel organ. In 70% of the cases, they are found in the mandible, especially in the angulus and the ramus.
Typically males of 20–40 years are affected. Unlike most of the jaw cysts, they lead to the development of symptoms: patients see their doctor because of a swelling or an intraoral fistula. If multiple keratocysts are found, you should suspect (and exclude) basal cell naevus syndrome. The syndrome is characterised by several keratocysts and basal cell carcinoma of the skin. Anomalies of the vertebrae and the ribs, and intracranial calcification often co-occur.
Root resorption is rare, and keratocysts usually mimic odontogenic cysts in X-ray images. A multilobular appearance should always raise its suspicion.
Re-occurrence is about 55%, which is very high compared to other cyst types. Therefore, the follow-up of these patients is really important including regular orthopantomograms (OPT).
The wall of keratocysts is relatively thin, and small, fragile accompanying cysts may be present. The ultimate rule of treatment is radical excision, that is, portions of the healthy bone are also removed to minimise re-occurrence.
Odontogenic cysts of inflammatory origin
Radicular, residual and periodontal cysts belong to this group.
The lining of these cysts is made up of non-keratinised stratified squamous epithelium.
Radicular cysts
It is the most frequently seen odontogenic cyst. It is always periapical and of inflammatory origin, usually because of the necrosis of the pulp, but it is not clear why in some cases a radicular cyst, and in others a periapical granuloma is formed. It is assumed that after a given time, all granulomas would turn into cysts, but endodontic treatment or extraction stops this process. The lining is derived from the epithelial islets of Malassez.
Clinically, it is a hard swelling around the apex of the affected tooth, which does not cause any symptoms most of the time. Symptoms occur if the cyst gets superinfected leading to the development of a subperiosteal, submucous or subcutaneous abscess.
A panoramic radiogram and periapical images are prerequisites for the diagnosis. Around the apex, a circumscribed area of radiolucency with a sharp edge is seen, and the periodontium is difficult to differentiate in this area.
The wall of the cyst is made up of collagen-rich connective tissue. Degeneration is extremely rare.
Treatment depends on whether the tooth is preserved or extracted. If the tooth is extracted, the cyst is removed at the same time. If preservation is possible, the cyst is removed, and apical resection is also performed.
Residual cysts
If the removal of the radicular cyst is not entirely successful, the remnants of the cyst may get resorbed spontaneously. If they persist (and they are not removed), they are called residual cysts. The X-ray image is similar to that of the radicular cyst without the tooth. Thorough and careful periapical curettage can prevent such complications.
Periodontal cysts
PATHOLOGY
It differs from the radicular cyst only in its position. The typical site is the cervical third of the root, and the background condition is periodontal inflammation.
NON-ODONTOGENIC CYSTS
This group of cysts originates in epithelial residues that get trapped between the facial processes as they unite in the development of the face. They can be found both in bones and in soft tissues.
Incisive canal cysts
Theoretically they are independent of age but seen most often between 30–50 years. A frontal palatal swelling may call our attention to it, but most often it is discovered as an X-ray by-finding. The typical finding of it in an X-ray image is oval or heart-shaped, mostly symmetrical, sharp-edged radiolucency. Sometimes it pushes the roots of the incisors apart, making it difficult to be differentiated from a radicular cyst. An important diagnostic sign is the cold-sensitivity of the affected tooth. Removal is indicated only if it causes subjectively disturbing symptoms, as degeneration has never been reported.
Medial palatinal cysts
Practically the same as the previous one, in a more dorsal palatal situation, which makes it questionable if it is an independent pathological entity.
Globulomaxillary cysts
Situated between the roots of an upper lateral incisor and a canine, this cyst can dislocate the roots of the affected teeth, which is an obvious indication for surgical removal. In X-ray images, a circumscribed thinning is seen.
Medial mandibular cysts
Located in the midline of the mandible.
Nasolabial cysts (Klestadt’s cysts and also nasoalveolar cysts)
They are soft tissue cysts and are rare. The peak of its prevalence is between 30–40 years of age. They present as a soft swelling in the superior alveolobuccal groove, or on the floor of the nasal cavity near its opening. The nostril on the affected side may be slightly displaced upwards. Bone alterations can be seen in the X-ray image only in case of a large cyst. Therapy consists of surgical removal.
Lateral neck cysts
All ages are affected, but they are most frequent in 21–30 years of age. They are painless, fluctuating structures usually related to upper respiratory tract infections. They may be situated anywhere along the line of the sternocleidomastoid muscle between the mandibular angle and the clavicle. Therapy consists of surgical removal.
Lateral neck fistulas
Etiologically the same as the previous one, but here a fistula is formed. The fistula must be resected.
Medial neck cysts
Most frequently they develop in the first ten years of life. The cyst is situated in the midline of the neck, near the hyoid bone. It is a soft swelling of 1–2 cm diameter, sometimes with a fistula.
Dermoid and epidermoid cysts
These are found in the skin but also in the floor of the mouth. They usually develop from embryonic epithelial tissue, and they have a stratified squamous epithelial lining.
The difference between dermoid and epidermoid cysts is the lack of the accessory structures of the skin in the latter one (e.g., sebaceous glands, hair follicles, sweat glands).
PATHOLOGY
Therapy consists of eradication of the cyst.
Heterotopic gastrointestinal cysts
In rare cases, heterotopic gastric epithelium is found in the oral cavity, which can give rise to cysts.
PSEUDOCYSTS
They are not real cysts as they have no epithelial lining. The most prevalent form is the simple bone cyst occurring characteristically in young patients and usually in the mandible. In X-ray images, the edge is not as sharp as that of odontogenic cysts, sometimes blurred and lacerated. On the bony wall, there is little fibrotic tissue and no epithelium. As a therapeutic intervention, excochleation is performed.