Tension-Type Headache: This is often characterized by a band-like pressure around the head, including the occipital region, and may not always respond to NSAIDs, especially if the dosage is inadequate or the frequency of administration is insufficient. The normal MRI supports this diagnosis, as tension-type headaches typically do not have an identifiable structural cause.

Cervicogenic Headache: Originates from the cervical spine and can refer pain to the occipital region. Normal MRI findings do not rule out this condition, as the cause can be related to soft tissue or joint dysfunction not visible on MRI.
Occipital Neuralgia: Involves the occipital nerves and can cause severe, sharp, or stabbing pain in the occipital region. It may not respond to NSAIDs alone and requires specific treatment targeting the nerve.
Myofascial Pain Syndrome: Can cause headaches, including those localized to the occipital area, due to muscle tension and trigger points. This condition might not respond to NSAIDs if the underlying muscle issues are not addressed.

Subarachnoid Hemorrhage (SAH): Although the MRI is normal, a very small SAH might not be visible, especially if the MRI was done too early or with inadequate sequences. The sudden onset of a severe headache, even if occipital, warrants consideration of SAH.
Giant Cell Arteritis: Can cause headaches, including those in the occipital region, and is a medical emergency due to the risk of vision loss. Normal MRI does not rule out this condition, as the diagnosis is typically made through clinical presentation, elevated ESR/CRP, and temporal artery biopsy.
Meningitis: Although less likely with a normal MRI, certain types of meningitis (e.g., viral) might not show significant abnormalities on imaging. The presence of fever, neck stiffness, and altered mental status would increase suspicion.

Chiari Malformation: Although an MRI is typically diagnostic, very mild cases might not be apparent, or the imaging might have been misinterpreted. Symptoms can include occipital headaches, especially with coughing or straining.
Eagle Syndrome: Involves an elongated styloid process or calcified stylohyoid ligament, which can cause referred pain to the occipital region. This condition is rare and might require specific imaging views or CT scans for diagnosis.
Atlantoaxial Subluxation: Can cause occipital headaches due to instability or misalignment of the upper cervical spine. This condition might not be evident on a standard MRI of the brain but could be visible on cervical spine imaging.