To report a case of proptosis occurring during a Valsalva maneuver in a neurofibromatosis patient with an arachnoid cyst.

A 42-year-old man diagnosed with type I neurofibromatosis visited our hospital with a 20-year history of enophthalmos in the left eye. The patient also complained of exophthalmos during the abdominal straining. On exophthalmometry, a 4 mm enophthalmos was found. The patient also presented with a limited motion to the superior and lateral direction. There was an ocular pulsation corresponding to the heart rate. During the Valsalva maneuver, a marked exophthalmos of the left eye occurred. The patient had light brown spots on the skin of the face and body trunk. Following an orbital computed tomography (CT), defects of the left sphenoid bone were present. Posteriorly, an arachnoid cyst was found; however, there was a lack of varix. The archnoid cyst was also observed to expand into the orbit during the Valsalva maneuver and forward the globe.

To date, cases of proptosis occurring during a Valsalva maneuver by causes other than orbital varix are rare. Herein, the authors report a case with a review of literature.