Fibrous Dysplasia of the mandible is a benign, developmental bone disorder characterized by the replacement of normal bone with fibrous connective tissue and irregular bone trabeculae. It most commonly presents in children and young adults and iit may cause facial asymmetry, tooth displacement, or malocclusion.

1.OPG: Ground-glass opacity, bone expansion.

2.US: Hypoechoic, heterogeneous, with possible shadowing.

3.CT: Ground-glass density, cortical thinning, bone expansion.

4.MRI: T1WE (hypointense),T2WE ( Variable, mixed signal, possibly hyperintense in areas) with mild to moderate heterogeneous enhancement.

It is a benign tumor composed of mature adipose (fat) tissue. It typically presents as a soft, mobile, and painless mass under the skin. In the mandibular region, lipomas are rare and typically present as painless, slow-growing masses.

1. OPG: lipomas are not easily visible due to the absence of calcification or bony involvement.
2. US: lipomas appear as well-defined, homogeneous, hyperechoic masses in most cases.
3. .CT:lipomas are seen as well-circumscribed, homogeneous masses with fat attenuation. 
4. MRI: T1WI (hyperintense  masses), T2 WI (lipomas remain hyperintense maintaining a signal similar to that of fat tissue) and they also generally do not enhance with contrast, except for the surrounding capsule or internal septations, which may show mild enhancement if present.

A hemangioma is a benign vascular tumor characterized by an abnormal proliferation of blood vessels. They are typically non-aggressive, slow-growing, and can vary in size and appearance based on the type and location.

1. OPG: may appear as radiolucent (dark) areas with a honeycomb or sunburst pattern due to the vascular channels. 
2. US: hypoechoic or heterogeneous masses with varying degrees of internal vascularity and color Doppler may show increased blood flow within the lesion.
3. CT: can appear as radiolucent areas with fine osseous striations. Post-contrast images often show strong enhancement due to the vascular nature of the tumor.
4. MRI: T1WE (hypo or isointense depending on the amount of fat content and vascularity), T2WE (hyperintense) Hemangiomas show strong and homogeneous enhancement due to their high vascularization.

Langerhans Cell Histiocytosis (LCH) of the mandible is a rare disorder characterized by abnormal proliferation of Langerhans cells, leading to granulomatous lesions that can affect bones, including the mandible. The lesion typically presents in children or young adults and may manifest clinically with pain, swelling, tooth mobility, or pathological fractures.

1. OPG: Radiolucent lesion with possible "floating teeth" appearance.
2. US: Hypoechoic or heterogeneous mass (less commonly used).
3. CT: Osteolytic lesion with cortical destruction, no calcification.
4. MRI: T1WE (hypointense or isointense) T2 WE (hyperintense) and with post-contrast heterogeneous enhancement. 

Mandibular chondroma is a rare, benign cartilaginous tumor that originates from hyaline cartilage. It can arise within the bone (enchondroma) or on the bone surface (periosteal chondroma).They can occur in the condyle, ramus, or body of the mandible.

1. OPG: Radiolucent, well-circumscribed lesion with possible "snowflake" calcifications, cortical expansion.
2.  US: Hypoechoic, heterogeneous mass with possible calcification-related shadowing.
3.  CT: Well-defined, lobulated, mixed-density lesion with characteristic calcifications ("rings and arcs" or "popcorn"), cortical thinning.
4. MRI: T1WE (hypointense to isointense), T2WE (hyperintense with hypointense calcified areas) and mild to moderate peripheral enhancement.

A mandibular osteochondroma is a benign, well-defined, bony outgrowth that maintains cortical and medullary continuity with the underlying mandible. 

1. OPG: It typically presents as a radiopaque mass.
2. US: appears as a hyperechoic structure with acoustic shadowing.
3. CT: is depicted as a bony outgrowth.
4. MRI: T1WI (hypointensity of the bone), T2 WI (hyperintensity of the cartilage) and variable post-contrast enhancement.

Mandibular osteonecrosis refers to the death of bone tissue in the mandible due to impaired blood supply. It is most commonly associated with medication (mainly bisphosphonates), radiation therapy or trauma. 

1. OPG: Mixed radiolucent and radiopaque changes with cortical disruption, sequestra, and possible pathologic fractures in advanced stages.
2. US: useful for detecting associated soft tissue abscesses.
3. CT: Excellent for evaluating bone destruction, sequestration, and cortical disruption. 
4. MRI: T1WI (low signal in necrotic bone), T2 WI (variable) and absent enhancement in necrotic regions.

A simple bone cyst is a benign, fluid-filled cavity found within the bone. It is commonly asymptomatic and incidentally discovered on imaging. 

1. OPG: it appears as a well-defined unilocular radiolucency.
2. US: The cyst shows as an anechoic, thin-walled, avascular lesion, typical of fluid-filled cavities.
3. CT:  It presents as a hypodense, well-circumscribed lesion with possible cortical thinning but no disruption, and a scalloped border between adjacent roots.
4. MRI: T1WI (hypointense), T2 WI (hyperintense) and absent no significant post-contrast enhancement.

A Stafne cyst is a benign, asymptomatic bone lesion typically located in the posterior region of the mandible. It represents a cortical bone depression filled with salivary gland tissue, most commonly from the submandibular gland.

1. OPG: it appears as a unilocular radiolucency with no signs of aggressiveness.
2. US: reveals a hypoechoic structure without vascularity.
3. CT:  demonstrates a cortical depression filled with soft tissue density.
4. MRI: T1WI (hypointense), T2 WI (hyperintense) and no significant post-contrast enhancement.

Mandibular osteosarcoma arises from osteoblasts and is characterized by uncontrolled production of immature bone or osteoid tissue.

1. OPG: it presents as a mixed radiolucent-radiopaque lesion with possible "sunburst" periosteal reactions and root resorption.
2. US: shows a hypoechoic mass with irregular vascularity.
3. CT: reveal a destructive lesion with mixed lytic and sclerotic areas, cortical destruction, and periosteal reactions.
4. MRI: T1WI (hypointense), T2 WI (hyperintense)  and heterogeneous enhancement after contrast administration, with clear delineation of soft tissue involvement. 

Mandibular squamous cell carcinoma  is a malignant tumor that arises from the epithelial cells of the oral cavity and can involve the mandible. 

1. OPG: ill-defined radiolucent lesion on with signs of bone resorption.
2. US: shows a hypoechoic mass with irregular margins and increased vascularity.
3. CT: reveal an infiltrative lesion with osseous destruction, heterogeneous enhancement, and potential lymph node involvement.
4. MRI: T1WI (hypointense), T2 WI (hyperintense) and strong enhancement on post-contrast sequences.

Plasmacytoma is a rare plasma cell neoplasm that can affect the mandible, either as a solitary lesion or as part of multiple myeloma.

1. OPG: appears as a radiolucent, expansile lesion with possible cortical destruction, resembling a "punched-out" defect.
2. US: Shows a hypoechoic mass with irregular borders, potentially with increased vascularity on Doppler.
3. CT: Displays a lytic, expansile lesion with cortical destruction and possible soft tissue extension, without calcification and can show contrast enhancement if there is soft tissue involvement
4. MRI: T1WI (hypointense), T2 WI (hyperintense)  and heterogeneous enhancement on post-contrast sequences.

Metastatic lesions to the mandible are relatively rare, the imaging characteristics of mandibular metastases vary depending on the primary tumor, the extent of involvement, and the tissue response. 

1. OPG: Metastases appear as osteolytic or osteoblastic lesions, often with cortical destruction, tooth displacement, or a "moth-eaten" appearance.
2. US: Shows a hypoechoic mass with poorly defined borders, possibly with increased vascularity and adjacent soft tissue involvement.
3. CT: Reveals osteolytic or sclerotic lesions, cortical destruction, and soft tissue masses.
4. MRI: T1WI (hypointense), T2 WI (hyperintense)  and heterogeneous enhancement on post-contrast sequences.