Odontogenic cysts

General principles

In general, inflammatory odontogenic cysts have proliferative epithelium, and developmental odontogenic cysts have uniformly thin epithelium, although inflammation may lead to epithelial proliferation in the latter, and long-standing inflammtory cysts may have thin lining. The most common odontogenic cyst is the radicular cyst (>50% of cases) followed by the dentigerous cyst (20% of cases). Any odontogenic cyst may grow to a large size, involve multiple teeth, cause root resorption, cause clinical swelling, perforate the cortex, or involve the maxillary sinus. Because the ectomesenchyme derived from neural crest is involved in odontogenesis, melanin occasionally may be identified in odontogenic cysts and tumors.

Clinical and radiographic findings

• The radicular cyst or granuloma is usually seen in adults, may be asymptomatic or painful (if an abscess is present), and may manifest as a swelling within the maxillary or mandibular sulcus, or on the face, depending on its size and severity of infection.

• A well-circumscribed radiolucency is present at the apex (apical radicular cyst or periapical granuloma representing >95% of cases) or on the side ( lateral radicular cyst or lateral radicular granuloma from a lateral accessory canal) of a nonvital tooth that may or may not have had prior root canal/endodontic therapy ( Fig. 14.4 A–G).

  

• A residual cyst refers to any odontogenic cyst in the alveolar bone where a tooth had been extracted and is most often a residual apical radicular cyst because of statistical frequency ( Fig. 14.4 H–I).

• A cyst may be curetted from the socket of an extracted nonvital tooth ( Fig. 14.4 J). Some radicular cysts can cause vestibular swelling ( Fig. 14.4 K–L).

Etiopathogenesis and histopathologic features

Inflammation from the pulp of necrotic teeth extends into the bone and results in stimulation and proliferation of rests of Malassez, which are remnants of the Hertwig root sheath that forms the roots of the teeth during odontogenesis.

• A radicular cyst is lined by nonkeratinized stratified squamous epithelium that usually proliferates in a plexiform, interlacing pattern and exhibits spongiosis and neutrophilic transmigration; long-standing lesions may show a more uniformly thin epithelium resembling that of developmental cysts ( Fig. 14.5 A–E).

  

• Radicular cysts from the apices of maxillary molars and maxillary anterior teeth may contain mucous cells or be lined by respiratory epithelium ( Fig. 14.5 F–G). Fragments of sinus mucosa, however, signify an oroantral communication and must be reported. Fragments of sinus inflammatory polyps may be present composed of masses of edematous fibrovascular tissue exhibiting few to no mucous glands, eosinophilic coagulum, and often eosinophils ( Fig. 14.6 ).

  

• The wall is composed of edematous granulation tissue and often scar tissue with many plasma cells, Russell bodies, lymphocytes, and foamy macrophages. Cholesterol granulomas from hemorrhage consist of needle-shaped, clear clefts surrounded by macrophages, and multinucleated foreign body-type giant cells ( Fig. 14.7 A); curetted specimens may show only such granulation tissue with variable amounts of lining epithelium ( Fig. 14.5 H).

  

• Some lesions exhibit a proliferation of nests of benign squamous epithelium referred to as “squamous odontogenic tumor-like proliferations” (see later in dentigerous cyst) and curetted lesions from anterior teeth often show abundant skeletal muscle ( Fig. 14.7 B–D).

• Rushton bodies are brightly eosinophilic, hyaline, lamellar, or globular structures of odontogenic origin often seen within the epithelium, sometimes exhibiting dystrophic calcifications. These are composed of K17, hair keratin, and hemoglobin alpha chain, and sometimes they may resemble the globular rose-pink enameloid of adenomatoid odontogenic tumor. These can sometimes extrude into the wall of the cyst ( Fig. 14.8 ).

  

• Foreign material is frequently encountered in the wall of radicular cysts. Root canal filling material and cements are often present in apical biopsies: gutta-percha is yellowish or brownish green, granular, and homogenously refractile ( Fig. 14.9 A–C); AH Plus is an epoxy resin that contains zirconium, iron oxides, and calcium tungstate; it is spherical and refractile within an eosinophilic background ( Fig. 14.9 D), whereas mineral trioxide aggregate (a tricalcium silicate cement) is basophilic and granular, but with refractile, crystalline particles ( Fig. 14.9 E); amalgam tattoo may be present from a previous apicoectomy (root apex excision) (see Fig. 14.7 B); bioceramics are also common fillers and calcium hydroxide filler is present as refractile granules within macrophages ( Fig. 14.9 F–H).

  

• Hyaline ring granulomas consist of hyalinized pale eosinophilic rings with central and/or surrounding giant cells; foreign material sometimes is identified as are dystrophic calcifications. The hyaline material is negative for Type IV collagen and does not represent vascular basement membrane as was previously believed ( Fig. 14.10 A–B).

  

• Russell bodies are often seen, as are pyronine bodies likely nuclear debris from cell breakdown ( Fig. 14.10 C). Cemental tears composed of acellular osseous-like material may be encountered ( Fig. 14.10 D).

• Periapical granuloma (not a true granuloma but an “oma” of granulation tissue) is the diagnosis if lining epithelium is not present but other features as noted previously in the wall are present ( Fig. 14.11 ). Sheets of plasma cells and macrophages are common in radicular cysts and periapical granulomas, and they should not be overdiagnosed as plasmacytomas ( Fig. 14.12 ).

  
  

• Periapical granulomas often contain abscesses and woven bone is a common finding in apical lesions ( Fig. 14.13 ).

  

• Periapical scar shows only fibrosis, sometimes with chronic inflammation. Uncommonly, a traumatic neuroma may develop within the scar tissue (see Figs. 14.8 A and 14.14 A).

• Suction artifact that appears as ovoid-to-round spaces within the soft tissues is a common finding; the spaces contain wispy amorphous material that has been identified as alcianophilic acid mucopolysaccharides ( Fig. 14.14 B–C).

  

Differential diagnosis

• Chronic active periodontitis consists of granulation tissue lined by crevicular epithelium that is composed of similar nonkeratinized stratified squamous epithelium, which exhibits spongiosis and neutrophilic transmigration often in continuity with surface keratinized epithelium, but clinically the tooth exhibits a periradicular radiolucency ( Fig. 14.15 ). Disease starts either from an apical radicular cyst that grows very large and combines with an overlying periodontal bone defect (combined endodontic-periodontal inflammatory disease), or from periodontal disease starting from the surface of the bone and extending downward to encompass the entire tooth.

  

• An inflamed dentigerous cyst appears similar except that it surrounds an impacted tooth.

Management and prognosis

• Enucleation or curettage with apicoectomy (excision of the root tip) is curative.

Clinical and radiographic findings

• This occurs in children in the first decade with a mean age of 7 years with no sex predilection and 38% are bilateral; pain is almost always present with buccal swelling in approximately 50% of cases. A vital first permanent molar is the most frequently affected tooth.

• There is a radiolucency 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 and cone beam computed tomogram); a periosteal reaction may be present ( Fig. 14.16 A–C).

  

Etiopathogenesis and histopathologic features

The lining likely derives from crevicular epithelium and less likely from dental lamina rests. One theory is that buccal enamel extensions onto the tooth root causes pocketing and proliferation of the crevicular epithelium. Since such extensions are a developmental anomaly, bilaterality would not be unusual. Another theory of pathogenesis is that this arises from a laterally displaced dentigerous cyst of the first molar, which could also explain the high incidence of bilaterality.

• The histopathology is similar to that of a radicular cyst with nonkeratinized stratified squamous epithelium exhibiting plexiform proliferation, spongiosis and neutrophilic transmigration, and acute and chronic inflammation within the wall ( Fig. 14.16 D).

Differential diagnosis

• If the tooth is nonvital and the cyst is unilateral, a lateral radicular cyst from a lateral accessory canal of the devitalized tooth should be considered.

• Some clinicians consider the buccal bifurcation cyst to be a subcategory of paradental cysts , which are cysts located to the side of a tooth; however, categorizing a cyst based on anatomic site alone rather than etiopathogenesis is not useful; many so-called paradental cysts are distal to third molars and they are more likely to be dentigerous cysts (see later).

Management and prognosis

• Enucleation of the cyst without extraction of the tooth is curative.

Clinical findings

• These usually occur in the fifth or sixth decade with 60% occurring in women; it appears as a bluish, slightly fluctuant, dome-shaped nodule on the attached gingiva or alveolar mucosa; these cysts are most frequent in the mandibular canine-premolar area (70%–80% of cases), with the second most common site being the maxillary canine-lateral incisor area; some cases are multiple or bilateral ( Fig. 14.17 A and B).

  

Etiopathogenesis and histopathologic features

Gingival cyst of the adult arises from dental lamina rests of Serres in the gingiva that undergo cystic change and enlargement ( Fig. 14.17 C).

• The cyst is lined by nonkeratinized, low cuboidal, or squamous epithelium usually two to four cells thick; epithelial plaques and whorls containing glycogen-rich clear cells are often present and microcystic and ductlike structures may be seen ( Figs. 14.18 ). Infrequently, the epithelium may be keratinized ( Fig. 14.19 ) and rarely, bona fide gingival KCOT/OKC has been reported.