Spontaneous regression of an interhemispheric arachnoid cyst: illustrative case

Abstract

Background: Intracranial arachnoid cysts are benign collections of cerebrospinal fluid that are often asymptomatic and discovered incidentally. An interhemispheric location of these lesions is rare, with only a few such cases reported in the literature. Though spontaneous regression of arachnoid cysts has been described in other locations, to date this phenomenon has not been reported in interhemispheric fissure cysts.

Observations: In this report, we describe a patient with a large, multiloculated interhemispheric arachnoid cyst diagnosed on prenatal ultrasound. She did not exhibit neurologic deficits or signs of increased intracranial pressure and was observed with serial imaging. After several years of observation, imaging revealed spontaneous and progressive decrease in the cyst size.

Lessons: We illustrate a case of regression of an interhemispheric arachnoid cyst in a pediatric patient. To our knowledge, this is the first reported case of spontaneous shrinkage of an arachnoid cyst in this location. Although the current presentation is rare, this reporting adds to the current understanding of natural history of arachnoid cysts and provides an example of radiographical improvement without intervention of a cyst located within the interhemispheric fissure.

Keywords: Arachnoid cyst; Interhemispheric cyst; Pediatric; Spontaneous regression.

Fig. 1

A Sagittal (upper) and coronal (lower) brain fast sequence magnetic resonance imaging (MRI) on day 2 of life, demonstrating a large cluster of extra-axial cystic structures at the medial aspect of the left parietal lobe extending inferior to the quadrigeminal cistern with mass effect on the adjacent brain and left lateral ventricle, as well as hypoplastic posterior corpus callosum. B Sagittal (upper) and coronal (lower) brain fast sequence MRI at 6 years of age, showing decrease in size of the cyst. C Sagittal (upper) and coronal (lower) brain fast sequence MRI at 8 years of age, which showed further decrease in size in the cyst