Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 59, Num. 4, 2011, pp. 499-500

Neurology India, Vol. 59, No. 4, July-August, 2011, pp. 499-500

Editorial

The application of intraoperative fluorescence utilizing 5-aminolevulinic acid in detection of residual cerebellar hemangioblastoma following visually assessed gross total resection

Mark K Lyons

Department of Neurological Surgery, Mayo Clinic, AZ, USA
Correspondence Address: Mark K Lyons, Department of Neurological Surgery Mayo Clinic Arizona, 5777 East Mayo Boulevard, Mayo Clinic Hospital 5 East, Phoenix, AZ 85054, USA, lyons.mark2@mayo.edu

Date of Submission: 17-Apr-2011
Date of Decision: 17-Apr-2011
Date of Acceptance: 18-Apr-2011

Code Number: 11158

PMID: 21891921

DOI: 10.4103/0028-3886.84325

Central nervous system hemangioblastomas account for approximately 2% of intracranial tumors and up to 10% of posterior fossa tumors. ^[1] These are benign tumors with an abundant vascular supply and occur mostly sporadically, but up to 30% are associated with von Hippel-Lindau disease (VHL). ^[2],[3] The tumors can be cystic or solid, majority of posterior fossa tumors are cystic and tumors arising in the brain stem and spinal cord are solid. ^[1],[4] Surgical techniques, neuroanesthesia and improved neuro-imaging have markedly reduced operative morbidity and mortality. The goal of surgical treatment is complete resection of the tumor. However, recurrence of the tumor at the original resection site is not uncommon. ^[2],[3] The use of orally administered 5-aminolevulinic acid (5-ALA), which is metabolized to protoporphyrin IX (PPIX) in the tumor cells, in intracranial tumor resection surgery has been well-documented. In addition, the photoxicity of PPIX has been utilized for photodynamic therapy as an adjunct tool in the treatment of brain tumors for many years. A recent report by Johansson and coworkers looked at the PPIX concentration in grade III versus grade IV gliomas. ^[5] They noted a large discrepancy in the distribution of the PPIX concentration within the grade IV tumors. The PPIX was noted to be much lower in the infiltration zones and necrotic areas of the tumor as compared to the more vital tumor components. ^[5] Whether this observation is related to the varying degree of vascularity in these heterogeneous areas of grade IV gliomas is a possibility. The application of this technique to cerebellar hemangioblastomas has not previously been reported in any case series.

Utsuki and colleagues report on their study of nine patients with cerebellar cystic hemangioblastomas utilizing intraoperative photodynamic 5-ALA to detect residual tumor following visually assessed gross total resection. ^[6] Protoporphyrin IX is the metabolite of 5-ALA which accumulates in tumor cells. Following visually confirmed gross total resection of the tumor, the resection cavity was irradiated with 405-nm excitation light using a semiconductor laser looking for any PPIX fluorescence, which would be consistent with residual tumor. In two of the nine cases, there was fluorescence of the cyst wall, not adjacent to the attachment of the tumor nodule, suggesting residual tumor cells. In both cases, there was histopathological confirmation of tumor cells in the additionally resected fluorescent cyst wall. This is an important observation, in that resection of the cyst wall at locations not at the attachment point of the tumor nodule is often not considered necessary when resecting cystic hemangioblastomas. The cyst wall is composed primarily of reactive non-neoplastic tissue. ^[3],[7],[8] Overall recurrence rates of hemangioblastomas are reported as high as 27%, and believed to most often be due to incomplete tumor nodule resection at the time of the initial surgery. ^[2],[3],[7] However, as Utsuki et al. points out there are cases of recurrent cystic cerebellar hemangioblastoma secondary to infiltration of tumor cells into the cyst wall. The rates of recurrence may be higher in patients with VHL, especially in those patients with solid tumors without a cystic component. ^[1] In addition, recurrences in VHL patients are often not at the site of the original tumor nodule.

The use of intraoperative indocyanine green fluorescence videography, more often applied to ophthalmological and aneurysm surgery, has also been used as an intraoperative tool for assessing complete extent of resection of spinal and cerebellar hemangioblastomas. ^[4] This technique, however, relies on the presence of the vascular blush to predict residual tumor as opposed to the direct uptake of the metabolite PPIX in the tumor cells. Consequently, the fluorescence of the tumor wall with 5-ALA may be more sensitive to residual tumor in cases of cystic cerebellar hemangioblastomas than indocyanine green despite its ability to visualize perforating arteries a millimeter or smaller in size. The authors conclude that using intraoperative photodynamic diagnosis via 5-ALA can aid in achieving a true gross total resection of the hemangioblastoma beyond what may be capable even with microscopically enhanced direct visual inspection.

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