10: Cysts and odontogenic tumours

Cysts and odontogenic tumours

10.1 General features

A cyst is a pathological cavity, not formed by the accumulation of pus, with fluid or semi-fluid contents.

Classification of cysts

Cysts can be classified on the basis of:

Box 10.1 lists the cysts found in the orofacial region using these groups.

10.2 Examination

General clinical features

Cysts may be detected because of clinical symptoms or signs (Table 10.1). Occasionally an asymptomatic cyst may be discovered on a radiograph taken for another purpose. Symptoms may include:

The most important clinical sign is expansion of bone. In some instances, this may result in an eggshell-like layer of periosteal new bone overlying the cyst (Fig. 10.2). This can break on palpation, giving rise to the clinical sign of ‘eggshell cracking’. If the cyst lies within soft tissue or has perforated the overlying bone, then the sign of fluctuance may be elicited by palpating with fingertips on each side of the swelling in two positions at right angles to each other.

If a cyst becomes infected, the clinical presentation may be that of an abscess, the underlying cystic lesion only becoming apparent on radiographic examination.

Radiological examination: general principles

As a basic principle, radiological examination should commence with intraoral films of the affected region; for small cystic lesions, intraoral films may be all that is needed for diagnosis, while for all cysts the fine detail of intraoral radiography will help to clarify the relationship between lesion and teeth. For larger lesions, more extensive radiography is appropriate. Selection of films should take account of the value of having two views with differing perspectives (preferably at right angles to each other; Fig. 10.2).

Radiological signs

Classically, cysts appear as well-defined round or ovoid radiolucencies, surrounded by a well-defined margin.

10.3 Specific cysts

Radicular cyst

Pathology

The cyst lumen is lined by a layer of simple, non-keratinising, squamous epithelium of variable thickness, which may display areas of discontinuity where it is replaced by granulation tissue or mural cholesterol nodules. Arcades and strands of epithelium may extend into the cyst capsule, which is composed of granulation tissue infiltrated by a mixture of acute and chronic inflammatory cells. This infiltrate reduces in intensity as the more peripheral areas of the cyst capsule are approached, where mature fibrous tissue replaces the granulation tissue (Fig. 10.4).

Several features associated with inflammatory odontogenic cysts may be present in the cyst lumen, lining and capsule: cholesterol clefts, foamy macrophages, haemosiderin and Rushton’s bodies.

Odontogenic keratocyst

Radiology

There is a well-defined radiolucency in odontogenic keratocysts, often with densely corticated margins. The outline may be ‘scalloped’ in shape. Occasionally, there is a multilocular appearance. Expansion is typically limited, with a propensity to grow along the medullary cavity (Fig. 10.5). This cyst was reclassified by The World Health Organization (WHO) in 2005 as keratocystic odontogenic tumour (KCOT) but the evidence for this reclassification is weak and it is likely to revert to odontogenic keratocyst at the next WHO edition.

Pathology

The cyst is lined by a continuous layer of stratified squamous epithelium of even thickness (5–10 cells), the surface of which is corrugated. The basal-cell layer is well defined, being composed of cuboidal or columnar cells that display palisading. This epithelium is most commonly parakeratinising, although orthokeratosis may be observed. The lumen of the cyst is filled with shed squames. The cyst capsule is composed of rather delicate fibrous tissue and is, classically, free from inflammation (Fig. 10.6). However, should the cyst become infected then an inflammatory infiltrate may be seen and the characteristic features of the epithelial lining will be lost.

The presence of daughter cysts within the capsule is a well-recognised finding, particularly in those odontogenic keratocysts arising as a component of the basal-cell naevus syndrome.

Dentigerous cyst

Gingival cysts

Gingival cysts are commonly found in neonates but are rarely encountered after 3 months of age. Many appear to undergo spontaneous resolution. White keratinous nodules are seen on the gingivae and these are referred to as Bohn’s nodules or Epstein’s pearls. Gingival cysts arise from the dental lamina and histologically are keratin containing. Many open into the oral cavity forming clefts from which the keratin exudes. Gingival cysts are lined by stratified squamous parakeratotic epithelium. In neonates and infants, the cysts are typically between 2 and 5 mm in diameter. They do not involve bone and no treatment is required.

Gingival cysts of adults are much less common and are found mainly in the buccal gingivae in the mandibular premolar–canine region. The cyst typically presents as a solitary soft blue swelling within the attached gingivae, seldom larger than 5 mm in diameter. Gingival cysts of adults are lined by a thin cuboidal or flattened epithelium resembling dental follicle. They do not extend into bone although they may rest in a shallow depression in the cortex. They are usually removed by excision biopsy for diagnosis.

Nasopalatine cyst

Radiology

The nasopalatine cyst appears as a well-defined, round radiolucency in the midline of the anterior maxilla (Fig. 10.9). Sometimes it appears to be ‘heart-shaped’ because of superimposition of the anterior nasal spine. Radiological assessment should include examination of the lamina dura of the central incisors (to exclude a radicular cyst) and assessment of size (the nasopalatine foramen may reach a width of as much as 10 mm).

Solitary bone cyst

10.4 Surgical management of cysts

Surgical management of cysts generally implies enucleation, but occasionally marsupialisation is the technique of choice. Some small radicular cysts do not require surgery and regress once the root canal of the associated tooth has been effectively cleaned and filled. Antibiotic therapy may be required if a cyst has become infected. Aspiration of fluid from a pathological cavity may be helpful in confirming the presence of cyst rather than maxillary sinus (air) or tumour (solid). Biochemical analysis of the aspirate indicating protein content of less than 40 g/l and cytology showing parakeratinised squames suggests an odontogenic keratocyst.

Enucleation

Enucleation of a cyst involves the removal of the whole cyst, including the epithelial and capsular layers from the bony walls of the cavity. This permits histopathological examination and ensures that no pathological tissue remains. A large mucoperiosteal flap, usually buccal, is raised to ensure that closure will be over adjacent sound tissues and not the bony cavity. Primary closure is nearly always undertaken unless the cyst is very infected, in which case this may be delayed and the cavity initially dressed with bismuth iodoform paraffin paste (BIPP) on ribbon gauze.

Enucleation of a nasopalatine cyst will require the raising of a palatal flap to provide surgical access and cyst removal. This inevitably damages the nasopalatine nerves and vessels and results in a small area of paraesthesia, which usually does not cause concern to the patient.

Marsupialisation

Marsupialisation is a simple operation that may be performed under local anaesthesia in which a window is cut and removed from the cyst lining. This allows decompression of the cyst, which then slowly heals by bone deposition in the base of the cavity. However, this technique permits histopathological examination of only a small and possibly non-representative sample of tissue. Primary closure is not undertaken but rather the cyst lining is sutured to the oral mucosa to keep the cavity open (Fig. 10.11). The cavity must be filled with a dressing such as BIPP, which must be frequently replaced, to prevent food debris trapping during the many months the cavity may take to heal. Alternatively, an extension may be added to a denture to protect the cavity, which becomes reduced in size as the cavity heals.

Marsupialisation is advocated when the cyst is so large that />

Jan 9, 2015 | Posted by in Oral and Maxillofacial Pathology | Comments Off on 10: Cysts and odontogenic tumours
Premium Wordpress Themes by UFO Themes