14 Odontogenic Cysts
The tooth develops from ingrowth of the lining of the primitive stomodeum called the dental lamina. The dental lamina forms tooth buds for the primary and the permanent dentition (Fig. 14-1), and after odontogenesis, remnant epithelium are left behind as rests. The epithelium of odontogenic cysts is thought to arise from stimulation of such residual odontogenic rests (e.g., rests of Serres in the gingiva or rests of Malassez around the tooth roots in the jawbones) (Fig. 14-2).
(From Young B, Lowe JS, Stevens A, Heath JW. Wheater’s Functional Histology: A Text and Colour Atlas. 5th ed. Edinburgh, Churchill Livingstone, 2007.)
Cystic lesions in the jawbones are either odontogenic or nonodontogenic in their derivation. All odontogenic cysts are inflammatory, developmental, or, less commonly, neoplastic in nature, and the putative epithelium from which they derive may be rests of Malassez, dental lamina rests, reduced enamel epithelium, degenerated enamel organ, or, in rare cases, the epithelium of the surface mucosa (Fig. 14-3). In general, inflammatory odontogenic cysts have proliferative epithelium, and developmental odontogenic cysts have uniformly thin epithelium, although inflammation may lead to epithelial proliferation. The most common cyst is the radicular cyst (>50%), followed by the dentigerous cyst and keratocystic odontogenic tumor (odontogenic keratocyst).
A tooth that has caries involving the pulp or that has experienced direct trauma becomes devitalized and may develop a radiolucency at the apex of the root. This may represent an apical radicular cyst, periapical granuloma or scar, or abscess.
• A cyst may or may not manifest as a swelling, depending on the size; the tooth may or may not be painful; a well-circumscribed radiolucency is present at the apex (apical radicular) or on the side (lateral radicular) of a nonvital tooth; there may have been prior root canal (endodontic) therapy (Fig. 14-4, A and B).
FIGURE 14-4 Apical radicular cyst. A, Circumscribed radiolucency at the apex of an endodontically treated left maxillary first premolar. B, Large circumscribed radiolucency centered around endodontically treated right lower first molar. C, Residual apical radicular cyst after extraction of the right maxillary first premolar.
(B, Courtesy of Dr. Manuel Diaz, private practice, Houston, Tex.)
• A radicular cyst is lined by nonkeratinized stratified squamous epithelium that usually proliferates in a plexiform or retiform pattern and exhibits spongiosis and neutrophilic exocytosis; the wall is composed of edematous granulation tissue and often scar tissue, many plasma cells, Russell bodies, lymphocytes, foamy macrophages, and sometimes abscesses are present (Fig. 14-5); curetted specimens may show only granulation tissue with focal lining epithelium (Fig. 14-6).
• Hyaline lamellar or globular structures of odontogenic origin (Rushton bodies) may be present within the epithelium (Fig. 14-7); epithelial loss is often associated with cholesterol granulomas.
• Foreign material from root canal filling is often seen: gutta percha is yellowish or brownish green, granular, and slightly refractile (Fig. 14-8); cements, in particular epoxy resin (such as AH Plus [Dentsply International, York, Pa], which contains zirconium and iron oxides and calcium tungstate), is usually refractile and crystalline in an eosinophilic background (Fig. 14-9); amalgam tattoo may be present from previous root apex excision (apicoectomy).
• Hyaline ring (pulse) granuloma (likely a foreign body reaction to exogenous material) consists of hyalinized rings with central and/or surrounding giant cells; foreign material is sometimes identified (Figs. 14-10 and 14-11).
• Radicular cysts from the apices of maxillary molars may be lined by respiratory epithelium (Fig. 14-12); fragments of sinus mucosa, however, signify an oroantral communication and must be reported; fragments of sinus inflammatory polyps may be present—exhibiting few to no mucous glands, eosinophilic coagulum, and eosinophils (Fig. 14-13).
FIGURE 14-8 Gutta percha (root canal filler). A, Brown-green granular foreign body commonly seen in apical lesions. B, Gutta percha is slightly refractile, and root canal cement is more brightly refractile.
FIGURE 14-9 Periapical granuloma with AH Plus (Dentsply International, York, Penn.) cement. A, Crystalline particulate foreign material with eosinophilic background. B, Particulate material is brightly refractile in polarized light.
FIGURE 14-10 Giant cell hyaline rings. A, Hyalinized rings often with giant cells in the center. B, Hyaline rings with giant cells, calcifications, and brown foreign material. C, Hyaline material negative for type V collagen.
FIGURE 14-12 Apical radicular cyst at apex of maxillary first molar. A, Cyst is partially lined by respiratory epithelium but without any mucous glands. B, Typical pseudostratified columnar epithelium (inset).
FIGURE 14-13 Sinus inflammatory polyp. A, Radiograph showing dome-shaped opacity (arrow) in the left sinus adjacent to carious left maxillary first molar and root tips of second molar. B, Mass of eosinophilic material and granulation tissue covered by respiratory epithelium with no mucous glands; many plasma cells and eosinophils (inset) (from A). C, Abundant eosinophilic amorphous material (from A).
(A, Courtesy of Dr. Jeffrey Stone, private practice, Lowell, Mass.)
• If epithelium is not present, the diagnosis is periapical granuloma (Fig. 14-14); sheets of plasma cells are common in periapical granulomas, and they should not be overdiagnosed as plasmacytomas (Fig. 14-15).
• Chronic active periodontal disease appears similar histologically, but clinically, the tooth is surrounded by a periradicular radiolucency; disease starts either from an apical radicular cyst that grows very large and combines with an overlying periodontal bone defect or from periodontal disease starting from the surface of the bone and extending downwards to encompass the entire tooth.
Mandibular Buccal Bifurcation Cyst
• Swelling and pain in the area of the first permanent molar; radiolucency around a vital first molar that extends from the furcation (where roots diverge) to the apex of the tooth causing tilting of the roots lingually (best seen on occlusal radiograph); periosteal reaction usually present (Fig. 14-17)
FIGURE 14-17 Mandibular buccal bifurcation cyst in one patient. A, Occlusal radiograph showing lingual displacement of roots of first molar on right and buccal radiolucency. B, Occlusal radiograph showing displacement of roots of first molar on left and buccal radiolucency.
(Courtesy of Dr. Bernard Friedland, Harvard School of Dental Medicine, Boston)
Lining may derive from dental lamina rests or crevicular epithelium. Another theory of pathogenesis is that this arises from a laterally displaced dentigerous cyst, which could explain the high incidence of bilaterality.