Prevalence and Pattern of Leptomeningeal Pigmentation in the Human Brain and Its Role in the Safe Surgical Excision of Extra-Axial Brain Tumors

Abstract

Background: Although leptomeningeal melanin pigmentation is well-known, it is not described in the neurosurgical literature. Dark pigmentation native to these transparent membranes might have microsurgical relevance in identifying a plane of dissection. Objective: To describe the prevalence of leptomeningeal pigmentation and determine whether its recognition helps during microsurgical excision of extra-axial brain tumors. Materials and Methods: This was a prospective cross-sectional observational study in cadavers and neurosurgical patients. Eight adult cadaveric brains were examined for leptomeningeal pigmentation and biopsies taken for histological studies. A total of 126 patients undergoing surgery for cerebellopontine angle and suprasellar lesions were included in the clinical study. The surgeon determined whether the recognition of pigmentation was useful during microneurosurgical arachnoid dissection. Results: Seven of 8 cadavers (87.5%) had leptomeningeal pigmentation on the ventral pons, optic chiasm, lamina terminalis, olfactory tract, and gyrus rectus and infrequently on the cerebral convexities. The prevalence of pigmentation was 76.9% in the clinical study, was seen in all pediatric patients, and was significantly higher in males (P = 0.009), with no significant association with skin color. Immunochemistry identified the pigmentation as melanin. Recognition of this pigmentation was deemed to be useful during tumor excision in 78% of the cases. Conclusions: Leptomeningeal melanin pigmentation has a prevalence of 76% to 87% in the Indian population and is more often seen in younger males. It is most commonly identified overlying the ventral brain stem and optic chiasm. Recognition of its presence is helpful during arachnoid dissection during most cerebellopontine angle and suprasellar tumor resections.