Introduction: Headaches are a common complaint in the emergency department and urgent care setting. There are some unusual causes that require further evaluation. One of these is arachnoid cysts.
Arachnoid cysts are fluid-filled sacs that occur in the arachnoid membrane that covers the brain (intracranial) or spinal cord (spinal). Primary arachnoid cysts are present at birth and are the result of developmental abnormalities during fetal growth. Secondary arachnoid cysts can be the result of injury, meningitis or a complication of brain surgery.

Case presentation: A 24 year-old woman presented to an urgent care clinic with chief complaint of headache. She reports significant increase in her migraine symptoms which started to limit her activities. After further evaluation, an outpatient CT scan was ordered. This study revealed a large arachnoid cyst producing mass effect and thereby causing significant herniation. The patient was transferred to a tertiary care center for neurosurgical consultation.

Final/working dx: The acute onset of worsening migraine symptoms in an otherwise health adult woman raises the suspicion of a more perilous diagnosis. The significant change in headache frequency and intensity led to further imaging to rule out secondary causes. Diagnosis of an arachnoid cyst was confirmed in this case. Treatment depends on the location and characteristics of the cyst.

Management/Outcome: This case illustrates an uncommon diagnosis in patients with headache. Any change in baseline of a patient’s headaches should warrant further evaluation. The previous clearance of the patient in other clinics should not cloud one’s clinical decision making. Patients diagnosed with arachnoid cysts should be evaluated by a neurosurgeon. Management options range from no treatment to surgical repair with shunt or fenestration.