Viral meningitis: This condition is a common cause of a bulging fontanelle in infants, resulting from inflammation of the meninges due to a viral infection. The bulge is often accompanied by other symptoms such as fever, irritability, and poor feeding.

Bacterial meningitis: Similar to viral meningitis but caused by bacterial infection, which can lead to more severe complications if not promptly treated. Symptoms include fever, lethargy, and signs of increased intracranial pressure.
Hydrocephalus: A condition characterized by an accumulation of cerebrospinal fluid (CSF) within the brain, leading to increased intracranial pressure and a bulging fontanelle. It can be congenital or acquired.
Trauma: Head injuries can cause a bulging fontanelle due to hemorrhage or edema. The history of a recent fall or trauma is crucial for this diagnosis.

Brain tumor: Although rare in infants, brain tumors can cause increased intracranial pressure, leading to a bulging fontanelle. Early detection is critical for treatment and prognosis.
Subarachnoid hemorrhage: Bleeding into the space surrounding the brain can increase intracranial pressure and cause a bulging fontanelle. This condition requires immediate medical attention.
Intracranial hemorrhage: Bleeding within the brain tissue itself can also lead to increased pressure and a bulging fontanelle, necessitating urgent diagnosis and treatment.

Neurofibromatosis type 1: A genetic disorder that can lead to hydrocephalus or brain tumors, causing a bulging fontanelle among other symptoms.
Tuberculous meningitis: A rare but serious form of meningitis caused by Mycobacterium tuberculosis, which can lead to increased intracranial pressure and a bulging fontanelle.
Congenital infections: Such as toxoplasmosis, cytomegalovirus, or syphilis, which can cause hydrocephalus or other neurological abnormalities leading to a bulging fontanelle.