Cysts of Jaw
and Oral Cavity
Nonepithelialized cysts of the mandible or maxilla
may result from trauma with intermedullary hemorrhage, or they may be
manifestations of monostotic and polyostotic fibrous dysplasia (disseminated or
localized osteitis fibrosa) and generalized osteitis fibrosa, also called
cystic osteodystrophy (von Recklinghausen disease). Because the latter
conditions are systemic disorders of the bones or endocrine system (primary or
secondary hyperparathyroidism), they will not be discussed in this volume. The
lesions are more often solid than fluid in content and are recognized as cysts
chiefly by their radiographic appearance.
The epitheliated cysts of the
jaws are etiologically divided into radicular, follicular, and facial cleft
cysts. The periapical or radicular cyst has an inflammatory basis
and evolves from a granuloma at the root apex of a tooth devitalized by caries or trauma. Bacteria and toxins of the infected pulp
canal stimulate proliferation of epithelial remnants left in the periodontal
membrane from Hertwig sheath, after it has been ruptured and fragmented by the
developing tooth. Eventually, this epithelium lines the necrotic center of the granuloma
and thickens, tending to isolate the inflammatory process. A fibrous capsule
develops outside the epithelial sac, and the lumen increases by transudation of
fluid. Round cell infiltration of the cyst membrane, including the adjacent
connective tissue and cellular debris, pus, macrophages, and cholesterol
crystals are usually found histologically. Even if the tooth with the granuloma
is removed, the cyst remains and may even expand more rapidly as a sterile
lesion.
The dentigerous or follicular
cyst arises from the enamel epithelium of the dental follicle forming
around the crown of an unerupted tooth. It is a benign, noninflammatory cyst
thought to be developmental in origin. Infection is present only when
contiguous teeth are coincidentally abscessed. The pathogenesis of follicular
cysts begins with retrograde changes and edema in the enamel organ, which, by
expansion, assumes various shapes above the developing crown. A simple
follicular cyst forms before enamel is excreted, arresting tooth maturation
or growing entirely separate from the tooth. A dentigerous cyst arises
at a later phase, after amelogenesis, and gradually envelops the crown, thus
interfering with eruption. The tooth may be forced by the cyst fluid to a site
remote from its normal position in the jaw. A follicular cyst is usually
unilocular, but multilocular forms occur. The most frequent location is the
mandibular third molar region. Until the cyst attains a large size and expands
the cortical plate of bone, the cyst may remain unrecognized. The buccal,
palatal, or alveolar bone may then bulge outward, or the maxillary sinus or
nasal cavity may be invaded. The wall of the cyst becomes parchment thin and
yields a crackling sound on palpation. Due to the pressure of the cyst and the
crowding of roots, the adjoining teeth are tilted when viewed on radiographic
imaging and unerupted teeth are displaced in total. Teeth are not devitalized
and resorption of roots is not encountered. A smooth, encapsulating layer of
cortical bone, a unilocular shape, and the absence of root erosion distinguish
a cyst from an invasive neoplasm, ameloblastoma, benign giant cell tumor, and
osteitis fibrosa localisata or generalisata. However, a cyst secondarily
infected from an adjacent tooth shows an obliterated capsule and appears
infiltrative. Also, a few cysts may be multilocular and cannot be completely
distinguished from ameloblastoma without biopsy examination. A layer of compact
bone borders the cyst sac, which is composed of fibrous connective tissue lined
with epithelium. The latter is stratified squamous, ranging from thin to a
considerable thickness; in some cysts, it may be simple columnar. The fluid
content is clear and straw colored, with an iridescent sheen imparted by
cholesterol crystals, or thick and cheesy from epithelial and hemorrhagic
debris.
Facial cleft cysts, also called fissural cysts, form at
the junction of the embryonic segments that fuse to make up the jaws. They may
be found at the median fissure of the palate, maxillary bones or mandible
(midline or median cyst), or nasoalveolar junction. The nasopalatine cyst, because
it is formed in the incisive canal or the incisive foramen from remnants of the
fetal nasopalatine communication, may be grouped with the facial cleft cyst.
Irritation or mucous secretions likely play an etiologic role in the more
superficial type. Ordinarily, a nasopalatine cyst presents no clinical
swelling, unless it is very large, and is detected only on radiographic
examination. A radiolucent area appears in the midline between the apices of
the central incisor teeth and is often misinterpreted as a radicular cyst. The
size varies from slight enlargement of the incisive fossa to one of a few
centimeters, involving a higher part of the incisive canal. If retention of
serous or mucoid secretion produces swelling in the region of the interincisive
papilla, discharge from the two tiny orifices on the side of the papilla may be
expressed. Secondary infection may occasionally ensue, producing a fluctuant
swelling of the palatal mucosa, resembling a dentoalveolar abscess.
Mucopurulent discharge then appears at the incisive outlets on pressure. In
edentulous mouths, resorption of the alveolar ridge may expose a nasopalatine
cyst that escaped previous detection.
Cysts of the oral mucous
membranes are retention cysts of the mucous glands or their ducts or,
occasionally, the sublingual salivary gland. The mucocele may appear on
the inner surface of the lips or cheeks, especially at a level parallel to the
occlusal plane, where chewing injuries cause obstruction of the mucous ducts. A
round, translucent, sometimes bluish swelling may range from a very minute size
to a centimeter. In the tongue, the glands of Blandin and Nuhn may form more
deeply seated mucoceles, which reach a considerable size, presenting a swelling
on the anterior ventral surface.
The ranula is named for
its resemblance to a frog’s belly; the term is a rather loose one applied to
cystic swellings of the floor of the mouth. A common error is to attribute a
ranula to obstruction of the submandibular (Wharton) duct, which in the
presence of a typical ranula is found patent. The most frequent cause is the
occlusion of an excretory duct of the sublingual gland. In a few cases, a
ranula may arise from the incisive glands in the midline or from the ciliated
cysts that carry epithelium (Bochdalek “glands”), which are derived from the
primitive thyroglossal duct. A typical ranula begins in the lateral anterior
floor of the mouth immediately beneath the mucous membrane. It usually grows
slowly, but rapidly developing cystic swellings (acute ranulas) are also known.
The color is bluish gray, with numerous small vessels well outlined. Palpation
gives a decided impression of fluid confined by an elastic membrane; the wall
may rupture spontaneously but soon refills. As it reaches large proportions it
crosses the midline and shows a division marked by the frenulum, also
displacing the tongue and impeding speech. A ranula will sometimes bulge
downward toward the chin because a portion of the sublingual gland perforates
the mylohyoid muscle.
Dermoid cysts, owing their origin to inclusion of
ectodermal structures by the mesoderm during the embryonic development of the
head, usually become visible only in the second or third decade of life. They
are located in the midline beneath the chin or between the geniohyoid muscles
deep in the floor of the mouth, or in a lateral position beneath the angle of
the jaw. The cyst consists of a fibrous capsule lined with a stratified,
squamous epithelial membrane, with a cheesy or semisolid mass containing
sebaceous material and hair filling the lumen. Theoretically, teeth and other
appendages may be present. The dermoid may reach large proportions and protrude
in the neck or beneath the tongue as a soft or semifirm doughy lump that pits
on pressure and is not fluctuant. The color tends to be waxy or yellowish when
the mucosa is thin enough to reveal it.
