Single most likely diagnosis:
- Nasolacrimal duct cyst: This is the most common diagnosis for a cyst found medial to the cantus, as it is a common location for nasolacrimal duct cysts to form, often due to obstruction of the nasolacrimal duct.
Other Likely diagnoses:
- Dermoid cyst: These can occur in the medial canthal area and are typically present at birth, although they may not become apparent until later in life.
- Epidermoid cyst: Similar to dermoid cysts, epidermoid cysts can occur in this area and are usually benign.
- Sebaceous cyst: While less common in this specific location, sebaceous cysts can occur anywhere on the skin, including the medial canthal area.
Do Not Miss diagnoses:
- Basal cell carcinoma: Although less likely, basal cell carcinoma can present as a cystic lesion in the medial canthal area and is crucial to diagnose early due to its potential for local destruction.
- Squamous cell carcinoma: Similar to basal cell carcinoma, squamous cell carcinoma can present in this area and has a higher potential for metastasis, making early diagnosis critical.
Rare diagnoses:
- Lacrimal gland tumor: Both benign and malignant tumors of the lacrimal gland can present as a cyst or mass in the medial canthal area, although they are rare.
- Meningocele or meningoencephalocele: These are rare congenital anomalies where meninges or brain tissue herniates through a defect in the skull, potentially presenting as a cystic mass in the medial canthal area.