Cysts of the jaws

A cyst is a pathological epithelial lined cavity that fills with fluid or soft material and usually grows from internal pressure generated by fluid being drawn into the cavity from osmosis (hydrostatic pressure). The bones of the jaws, the mandible and maxilla, are the bones with the highest prevalence of cysts in the human body. This is due to the abundant amount of epithelial remnants that can be left in the bones of the jaws. The enamel of teeth is formed from ectoderm (the precursor germ layer to skin and mucosa), and so remnants of epithelium can be left in the bone during odontogenesis (tooth development). The bones of the jaws develop from embryologic processes which fuse together, and ectodermal tissue may be trapped along the lines of this fusion.^[1] This "resting" epithelium (also termed cell rests) is usually dormant or undergoes atrophy, but, when stimulated, may form a cyst. The reasons why resting epithelium may proliferate and undergo cystic transformation are generally unknown, but inflammation is thought to be a major factor.^[1] The high prevalence of tooth impactions and dental infections that occur in the bones of the jaws is also significant to explain why cysts are more common at these sites.

Cysts that arise from tissue(s) that would normally develop into teeth are referred to as odontogenic cysts. Other cysts of the jaws are termed non-odontogenic cysts.^[2] Non-odontogenic cysts form from tissues other than those involved in tooth development, and consequently may contain structures such as epithelium from the nose. As the cyst grows from hydraulic pressure it causes the bone around it to resorb, and may cause movement of teeth or other vital structures such as nerves and blood vessels, or resorb the roots of teeth. Most cysts do not cause any symptoms, and are discovered on routine dental radiographs.^[1] Some cysts may not require any treatment, but if treatment is required, it usually involves some minor surgery to partially or completely remove the cyst in a one or two-stage procedure.

Classification

Odontogenic cysts

Dental panoramic radiograph showing dentigerous cyst associated with an impacted lower right wisdom tooth in the right mandible (arrowed, appears on the lower left of the image).

Odontogenic cysts have histologic origins in the cells of the dental structures. Some are inflammatory while others are developmental.

• Radicular cyst is the most common (up to two thirds of all cysts of the jaws). This inflammatory cyst originated from a reaction to dental pulp necrosis.
• Dentigerous cyst, the second most prevalent cyst, is associated with the crown of non-erupted tooth.
• Odontogenic keratocyst, which now is considered as tumor, and therefore called Keratocystic odontogenic tumor. This lesion may be associated with the Nevoid basal cell carcinoma syndrome.
• Buccal bifurcation cyst which appears in the buccal bifurcation region of the mandibular first molars in the second half of the first decade of life.^[3]
• Eruption cyst; a small cyst in the gingiva as a tooth erupts, forming from the degenerating dental follicle
• Primordial cyst; previous thought to be a unique entity. Most primordial cysts have proven to be Keratocystic odontogenic tumors
• Orthokeratinized odontogenic cyst; a variant of the Keratocystic odontogenic tumor
• Gingival cyst of the newborn; an inclusion cyst from remanents of the dental lamina on a newborn gingiva
• Gingival cyst of the adult; a soft tissue variant of the lateral periodontal cyst
• Lateral periodontal cyst; a non-inflammatory cyst (vs a radicular cyst) on the side of a tooth derived from remanents of the dental lamina
• Calcifying odontogenic cyst; a rare lesion with cystic and neoplastic features and significant diversity in presentation, histology and prognosis
• Glandular odontogenic cyst; cyst with respiratory like epithelial lining and the potential for recurrence with characteristics similar to a central variant of low-grade mucoepidermoid carcinoma

Developmental/ Non-odontogenic cysts

There are several development cysts of the head and neck most of which form in the soft tissues rather than the bone. There are also several cysts, previously thought to arise from epithelial remanents trapped in embryonic lines of fusion, most of which are now believed to be odontogenic in origin or have an unknown etiology. Their names are included for the sake of completeness.

Developmental cysts of the jaws

• Nasopalatine duct cyst, the most common development jaw cyst, appears only in the mid-line of the maxilla.

Developmental cysts of the soft tissues around the jaws

• Palatal cysts of the newborn (Epstein's pearls)
• Nasolabial cyst (nasoalveolar cyst)
• Epidermoid cyst of the skin
• Dermoid cyst
• Thyroglossal duct cyst
• Branchial cleft cyst (Cervical lymphoepitelial cyst)
• Oral lymphoepithelial cyst

Developmental cysts of questionable etiology

• Globulomaxillary cyst
• Median palatal cyst
• Median mandibular cyst

Signs and symptoms

Cysts rarely cause any symptoms, unless they become secondarily infected.^[1] The signs depend mostly upon the size and location of the cyst. If the cyst has not expanded beyond the normal anatomical boundaries of the bone, then there will be no palpable lump outside or inside the mouth. The vast majority of cysts expand slowly, and the surrounding bone has time to increase its density around the lesion, which is the body's attempt to isolate the lesion. Cysts that have expanded beyond the normal anatomic boundaries of a bone are still often covered with a thin layer of new bone. At this stage, there may be a sign termed "eggshell cracking", where the thinned cortical plate cracks when pressure is applied. A lump may be felt, which may feel hard if there is still bone covering the cyst, or fluctuant if the cyst has eroded through the bone surrounding it.^[4] A cyst may become acutely infected, and discharge into the oral cavity via a sinus. Adjacent teeth may be loosened, tilted or even moved bodily. Rarely, roots of teeth are resorbed, depending upon the type of cyst. The inferior alveolar nerve runs through the mandible and supplies sensation to the lower lip and chin. As most cysts expand slowly, there will be no altered sensation (anesthesia or paraesthesia), since the inferior alveolar canal is harmlessly enveloped or displaced over time. More aggressive cysts, or acute infection of any cyst may cause altered sensation.

Diagnosis

Most cysts are discovered as a chance finding on routine dental radiography. On an x-ray, cysts appear as radiolucent (dark) areas with radiopaque (white) borders. Cysts are usually unilocular, but may also be multilocular. Sometimes aspiration is used to aid diagnosis of a cystic lesion, e.g. fluid aspirate from a radicular cyst may appear straw colored and display shimmering due to cholesterol content.^[4] Almost always, the cyst lining is sent to a pathologist for histopathologic examination after it has been surgically removed. This means that the exact diagnosis of the type of cyst is often made in retrospect.

Treatment

When treatment is required, this is usually by surgical removal of the cyst. There are four ways in which cysts are managed:^[1]

• Enucleation - removal of the entire cyst
• Marsupialization - the creation of a window into the wall of a cyst, allowing the contents to be drained. The window is left open, and the lack of pressure within the cyst causes the lesion to shrink, as the surrounding bone starts to fill in again.
• Enucleation following marsupialization - Sometimes marsupialization is carried out as a single procedure, but usually it is followed by a second procedure to remove the cyst. This is particularly the case when cysts are very large and their removal would leave a significant surgical defect.
• Enucleation with curettage - this is removal of the cyst and some of the surrounding bone, which may contain some of the lining of the cyst.

Prognosis

The prognosis depends upon the type, size and location of a cyst. Most cysts are entirely benign, and some may require no treatment. Rarely, some cystic lesions represent locally aggressive tumors that may cause destruction of surrounding bone if left untreated. This type of cyst are usually removed with a margin of healthy bone to prevent recurrence of new cysts. If a cyst expands to a very large size, the mandible may be weakened such that a pathologic fracture occurs.

Epidemiology

Radicular cysts are by far the most common cyst occurring in the jaws.^[4]

References