Odontogenic cysts

Odontogenic cysts are lined with epithelium derived from the following tooth development structures:

• rests of Malassez: radicular cyst, residual cyst
• reduced enamel epithelium: dentigerous cyst, eruption cyst
• Remnants of the dental lamina: Odontogenic keratocyst, lateral periodontal cyst, gingival cyst of adult, glandular odontogenic cyst

Radicular cyst    
    
Radiology

- A well-defined, round or ovoid radiolucency is associated with the root apex or, less commonly in the lateral position, of a heavily restored or grossly carious tooth.

- A corticated margin is continuous with the lamina dura of the root of the affected tooth.

- The appearances are similar to those of an apical granuloma, but lesions with a diameter exceeding 10 mm are more likely to be cystic
    
Pathology

The cyst lumen is lined by a layer of simple squamous epithelium of variable thickness, which may display areas of discontinuity where it is replaced by granulation tissue.

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 

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.
    
    
Residual cyst

Radiology

The residual cyst has a well-defined, round/ovoid radiolucency in an edentulous area. Occasionally flecks of calcification may be seen.

Pathology

The lining and capsule are similar to the radicular cyst; however, both appear more mature, with the former lacking the arcades and strands of epithelium extending into the capsule.    

Keratocystic odontogenic tumor-(Odontogenic keratocyst)

The orthokeratinizing odontogenic cyst is considered an unrelated entity without risk of recurrence or aggressive growth or association with Nevoid basal cell carcinoma syndrome

Epidemiology

- 4 - 12% of all odontogenic cysts (often compared to odontogenic cysts even though WHO classifies as tumor)
- Peaks in second and third decade of life, but can occur over wide age range
- 90% are solitary
- Multiple tumors seen in Nevoid Basal Cell Carcinoma Syndrome / Gorlin Syndrome

Sites

- Mandible most commonly involved (65 - 85% of KCOT)
- Most common site: posterior mandible
- Not uncommonly, but not exclusively associated with impacted teeth
- Rarely occurs in soft tissue

Pathophysiology

- Thought to arise from dental lamina
- Two-hit mechanism results in bi-allelic loss of PTCH ("patched") tumor suppressor on 9q22.3-q31 causing dysregulation of p53 and cyclin D1 oncoproteins

- 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.

Clinical features

- Often asymptomatic, incidentally discovered on Xray
- Can cause symptomatic swelling
- Symptoms of pain and drainage if secondarily infected
- Can cause local bone and soft tissue destruction, but usually spares teeth and roots

Radiology

- Small lesions often unilocular radiolucent lesion, variable sclerotic margins
- Larger lesions often multilocular, variable scalloped margins

Dentigerous cyst

Radiology
In dentigerous cysts, there is a pericoronal radiolucency greater than 3-4 mm in width that is suggestive of cyst formation in a dental follicle. The well-defined, corticated radiolucency is associated with the crown of an unerupted tooth. Classically the associated crown of the tooth lies centrally within the cyst, but lateral types occur . 

Pathology

The defining feature of a dentigerous cyst is the site of attachment of the cyst to the involved tooth. This must be at the level of the amelocemental junction. The lining of the cyst is composed of a thin layer of epithelium, either cuboidal or squamous in nature, some 2-5 cells thick . This lining is of even thickness and may  include mucous cells along with focal areas of keratinisation of the superficial epithelial cells. The cyst capsule is, classically, free from inflammation. However, in common with the odontogenic keratocyst, the normal features of the epithelial lining may be distorted when an inflammatory infiltrate is present.

Eruption cyst

Radiology

The extra-bony position of the eruption cyst means that the only radiological sign is likely to be a soft tissue mass.

Pathology

An eruption cyst is basically a dentigerous cyst in soft tissue over an erupting tooth. The histological features are similar to those of the dentigerous cyst, though reduced enamel epithelium is often seen.

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. 
Arise from epithelial rests of dental lamina epithelium (rests of Serres) within soft tissue
Many open into the oral cavity forming clefts from which the keratin exudes. 

Radiology

Cyst may cause a superficial "cupping out" of alveolar bone, usually not detected on a radiograph but apparent when cyst is excised
 

Regional Odontodysplasia

• Key Feature: Widened pre-dentin layer
• Histology: Large areas of interglobular dentin

Supernumerary Roots

• Most Common: Mandibular canines and premolars

Congenitally Missing Teeth

Permanent Teeth (Descending Order):

1. Third molar
2. Mandibular 2nd premolar
3. Maxillary lateral incisor
4. Maxillary 2nd premolar

Deciduous Teeth: Maxillary and mandibular lateral incisors

Exception Alert: Serum alkaline phosphatase is raised in all of the following except: ➡️ Osteogenesis Imperfecta

Mnemonics Flashcards

• SLE → IgG, IgM, IgA deposits at BMZ + superficial lamina propria
• Lichen Planus (Erosive/Atrophic) → Autoimmune T-cell; BMZ involvement
• Cicatricial Pemphigoid → Subepidermal blistering from anti-BMZ antibodies

• Blood: Aneurysmal bone cyst, Vascular lesion, Vessel puncture.

• Air: Traumatic bony cyst (Simple Bone Cyst/Hemorrhagic Bone Cyst), Maxillary sinus.

• Chocolate Colored Fluid: Warthin's Tumor (salivary gland cyst).