Fluorescence and immune-cell infiltration of nonneoplastic, postbrachytherapy brain tissue in 5-ALA–guided resection of recurrent anaplastic meningioma: illustrative case

Abstract

BACKGROUND

5-Aminolevulinic acid (5-ALA) fluorescence-guided surgery is a well-established technique for resecting high-grade gliomas. However, its application in meningiomas, especially those previously treated with radiation therapy, remains under investigation.

OBSERVATIONS

A 48-year-old female with recurrent anaplastic meningioma, World Health Organization grade 3, underwent a right-sided craniotomy using off-label 5-ALA as a surgical adjunct. The patient had previously undergone brachytherapy seed implantation (20 × cesium 131) for tumor management. During the surgery, a large fluorescent tumor mass adjacent to the brachytherapy-treated area was resected, and the prior brachytherapy seeds were removed. Interestingly, the surrounding brain tissue in the irradiated area showed robust 5-ALA fluorescence. Pathological examination confirmed that the fluorescent brain tissue was nonneoplastic and associated with lymphocyte and macrophage infiltration.

LESSONS

This case report presents unique 5-ALA fluorescence in nonneoplastic tissue following brachytherapy, which was found during the resection of recurrent anaplastic meningioma. This phenomenon may reflect an intricate interplay among radiation therapy, immune cells, the tumor microenvironment, and 5-ALA metabolism. Given that false-positive findings in fluorescence-guided surgery can lead to unnecessary tissue resection and increased surgical morbidity, further research is warranted to elucidate the mechanisms underlying this phenomenon and its implications for meningioma surgery.

5-Aminolevulinic acid (5-ALA) fluorescence-guided surgery (FGS) has gained prominence in recent years for its utility in high-grade glioma resection, allowing enhanced visualization and tumor removal.¹ The use of 5-ALA for meningioma surgery has also been reported.²

Mechanistically, 5-ALA is preferentially taken up by cells of certain tumors, including meningiomas, and enters the heme biosynthesis pathway, where it is converted to heme precursor porphyrin PpIX, which then accumulates in cells due to various tumor-specific aberrations, such as altered metabolic activity, increased cellular proliferation rates, and dysfunctional heme biosynthesis pathways.^3,4 PpIX has the unique property of absorbing light in the range of 375 to 440 nm and emitting violet-red fluorescence within the range of 640 to 710 nm when excited by blue or violet light. During surgery, this fluorescence can be visualized, helping surgeons to distinguish tumor tissue from normal brain tissue. In meningiomas, this fluorescence has been shown to be dose dependent but has not yet been correlated to the expression of specific enzymes and transporters, such as ferrochelatase and ATP-binding cassette subfamily B member 6, which are involved in PpIX metabolism and have been correlated with 5-ALA fluorescence in gliomas.^5–7 Thus, the exact mechanism of 5-ALA fluorescence in meningioma remains to be defined, but 5-ALA has consistently been shown to result in fluorescence of meningiomas in clinical studies.² A multicenter prospective study to determine the safety and benefit of 5-ALA FGS for meningiomas is currently ongoing.⁸

5-ALA FGS in patients with meningioma who have previously been treated with brachytherapy has not been well characterized.^9,10 Given that most patients with recurrent meningiomas receive and benefit from some form of radiotherapy,^11,12 the relationship between prior radiation therapy and 5-ALA fluorescence is a critical consideration. Here, we present a unique finding of 5-ALA fluorescence in nonneoplastic tissue adjacent to prior brachytherapy seeds during resection of a recurrent anaplastic meningioma.

Illustrative Case

A 48-year-old female first presented to our institution in January 2019 with headaches, leading to the discovery of a left parietal parasagittal meningioma on magnetic resonance imaging (MRI; Fig. 1A). She underwent a left parieto-occipital craniotomy in January 2019, in which pathology confirmed an atypical meningioma, World Health Organization (WHO) grade 2. The patient was offered adjuvant radiation treatment at that time but chose to defer further treatment. Postoperative imaging showed near-total resection (Fig. 1B). In October 2020, radiological disease progression (Fig. 1C) led to 54-Gy fractionated radiation therapy, completed in December 2020. In April 2022, the patient experienced a clinical seizure and further radiological disease progression (Fig. 1D). In May 2022, a repeat left parietal craniotomy with brachytherapy seed implantation (20 × cesium 131) was performed (Fig. 2A and B). The final pathology was anaplastic meningioma, WHO grade 3, with homozygous loss of CDKN2A, NF2 mutation, ARID1A deletion, and no TERT promoter mutation.

FIG. 1.

A: MRI showing a left parietal meningioma following patient presentation with headaches. B: Postoperative MRI after the first craniotomy. C: MRI from October 2020 showing the radiological recurrence of tumor, prompting radiation treatment. D: MRI from April 2022 showing the radiological progression of disease following a clinical seizure.

FIG. 2.

A: Postoperative MRI in May 2022 after a second craniotomy. B: Scan showing brachytherapy seed placement (20 × cesium 131). C: MRI in January 2023 showing new right-sided radiological progression of disease after the patient was symptomatic with headache. D: Overlay of May 2022 computed tomography from after the second craniotomy on the January 2023 MRI, showing both the brachytherapy seeds and recurrent tumor.

In January 2023, MRI revealed disease progression at the prior resection margin, with the largest portion measuring 38 × 13 × 15 mm. No gross tumor recurrence was observed at the brachytherapy seed placement site (Fig. 2C and D). Resection of the new right-sided lesion with the off-label use of 5-ALA as a surgical adjunct was planned.

The patient ingested 5-ALA approximately 3 hours preoperatively. A right-sided craniotomy was performed, incorporating part of the prior bone flap. A fluorescent mass was found to be herniating through an existing burr hole. After removing the bone flap, a large, fluorescent tumor was encountered (Fig. 3A). This was dissected off the dura, and the dura was opened sharply in a curvilinear fashion. Because additional tumor on the dural flap was noted (Fig. 3B), the dura was sharply excised so that no 5-ALA–fluorescent tissue remained. Prior brachytherapy seeds were removed (Fig. 4A). It was noted that a significant portion of the adjacent gliotic brain tissue exhibited robust 5-ALA fluorescence (Fig. 4B). This fluorescent tissue was equal in intensity to the recurrent tumor tissue. The fluorescence of this adjacent brain tissue was uniform centrally but was poorly circumscribed as compared with the recurrent tumor tissue shown in Fig. 3A and B. A frozen specimen of this fluorescent tissue confirmed postradiation gliosis and the absence of additional tumor cells. The patient was discharged uneventfully on postoperative day 3. Postoperative imaging showed expected postsurgical changes, with no findings suggestive of residual tumor.

FIG. 3.

A: A large, fluorescent tumor mass underneath the bone flap was resected. B: Additional fluorescent tumor on dura that was excised. C: Pathology of resected tumor showing marked mitoses and findings consistent with grade 3 anaplastic meningioma. D: Pathology of tumor showing areas of necrosis within the tumor. Hematoxylin and eosin, original magnification ×40 (C and D).

FIG. 4.

A: Removal of brachytherapy seeds (white arrow) that had been placed prior to the craniotomy. B: Fluorescent region near the brachytherapy seeds that was biopsied (white arrow). C: Pathology of the biopsied fluorescent tissue showing no tumor but with reactive gliosis and chronic inflammation. D: Perivascular lymphocytic infiltration observed in the biopsied fluorescent tissue. Hematoxylin and eosin, original magnification ×20 (C and D).

Final pathological findings confirmed anaplastic meningioma, WHO grade 3 (Fig. 3C and D). Pathological examination also confirmed that the nonneoplastic fluorescent tissue identified during the operation was normal brain tissue with reactive gliosis, chronic inflammation, and marked perivascular lymphocytic inflammation (Fig. 4C and D). CD3 staining revealed a significant number of perivascular and parenchymal T cells (Fig. 5A), and CD68 staining showed many macrophages and microglia in the reactive brain tissue (Fig. 5B). There were more CD68-positive cells per high-power field (HPF) than CD3-positive cells, indicating a myeloid predominance of the immune infiltrate rather than a predominance of lymphocytes.

FIG. 5.

A: CD3 staining of the fluorescent nonneoplastic tissue showing T-cell lymphocytes. B: CD68 staining of the fluorescent nonneoplastic tissue showing macrophages and microglia. Original magnification ×20 (A and B).

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Observations

Here, we report 5-ALA fluorescence in nonneoplastic brain tissue previously treated with brachytherapy, which was found during the resection of recurrent anaplastic meningioma. Prior studies have reported that 5-ALA enables intraoperative visualization of most intracranial meningiomas as well as tumor-infiltrated bone flaps. In addition, some nonspecific fluorescence has been noted during the resection of recurrent gliomas treated with external beam radiotherapy. This is the first report of particularly robust nonneoplastic 5-ALA fluorescence in tissue previously exposed to brachytherapy for a meningioma.

5-ALA fluorescence has been observed in perinecrotic nonneoplastic tissue from patients with high-grade glioma, particularly in cases of recurrent glioblastoma (GBM), as first reported by Miyatake and colleagues in 2007.¹³ These areas were characterized by acute inflammation with reactive astrocytes and macrophages, suggesting that inflammation secondary to radiation may be the driving factor. 5-ALA fluorescence has also been reported in normal brain parenchyma surrounding GBM with peritumoral inflammation, although the extent of this effect has been relatively limited.¹⁴ Additionally, edematous peritumoral tissue in brain metastases has been shown to fluoresce with 5-ALA.^15,16

In our case, the final pathological analysis demonstrated that areas of substantial fluorescence in nonneoplastic brain tissue were associated with significant lymphocyte and macrophage infiltration following brachytherapy. The immune infiltrate was predominantly myeloid (tumor-associated macrophages and microglia) in origin, as indicated by the increased number of CD68-positive cells per HPF. One hypothesized explanation is that lymphocytes, histocytes, and macrophages internalize 5-ALA, leading to an accumulation of porphyrin precursors.¹⁷ A recent study of high-grade glioma gene expression found that tumors with strong 5-ALA fluorescence–related mRNA expression signatures had greater immune cell infiltration, with tumor-associated macrophages as the predominant cell type.¹⁸ This evidence also supports the hypothesis that a portion of tumor fluorescence after 5-ALA administration may be related to myeloid cells such as tumor-associated macrophages that are present in the tumor rather than to tumor-intrinsic fluorescence. Tumor-associated macrophages have previously been shown to make up a large portion of gliomas^19,20 and were recently shown to also be present in meningiomas, where they can represent nearly 20% of the tumor.²¹ These proposed mechanisms of immune-related 5-ALA fluorescence both within and outside the tumor merit further investigation.

Our institution and others have previously described brachytherapy, a form of radiation therapy that involves the placement of radioactive seeds directly in or near the tumor, as a viable adjuvant treatment for recurrent, atypical, and anaplastic meningiomas, given the dose limitations of repeated external beam radiation.²² As with all radiation therapy, brachytherapy causes local tissue damage and destruction and may also stimulate immune cell infiltration and activation. Both high- and low-dose radiation are highly immunogenic and have recently become a promising combination therapy with immunotherapy for various solid tumors.^23,24 High-dose radiation has the capacity to release tumor-associated antigens and upregulate major histocompatibility complex class I to prime T cells, whereas lower doses can make the tumor microenvironment less immunosuppressive. In other cancers, high-dose brachytherapy has been shown to convert “immunologically cold” into more immunologically activated “hot” tissues,²⁵ and low-dose brachytherapy has been associated with increased T-cell activation.²⁶

5-ALA may improve the extent of resection in meningioma, particularly in higher-grade and/or recurrent cases. Postoperative tumor volume has been found to be a significant predictor of tumor recurrence in meningioma.²⁷ A large cohort study of 204 cases showed that 5-ALA–induced PpIX fluorescence was successful at enabling intraoperative visualization of most intracranial meningiomas as well as tumor-infiltrated bone flaps.²

The uptake of 5-ALA into cells of the brain, both normal cortex and tumor tissue, is predicated on 5-ALA bioavailability in the microenvironment. 5-ALA can cross the blood–brain barrier (BBB) but has variable bioavailability in brain regions with an intact BBB. Animal studies have shown that regions without a BBB, such as the meninges, have the highest amounts of porphyrin accumulation after intravenous 5-ALA injection.²⁸ This makes 5-ALA an appealing adjunct for meningioma, although nonspecific uptake in regions of normal tissue adjacent to these tumors may also ultimately confound intraoperative surgical decision making.

Although this is the first case report of nonspecific fluorescence around a recurrent meningioma after brachytherapy, the literature on glioma suggests that nonspecific fluorescence is most associated with recurrent tumors that have undergone adjuvant treatment.¹⁴ In our case, adjacent fluorescent areas were found on pathology not to contain any tumor cells. Further studies should elucidate the factors associated with this type of nonspecific fluorescence in meningioma, and caution should be exercised when relying on 5-ALA in these cases to prevent unnecessary tissue resection.

Lessons

In this case of an aggressive, recurrent meningioma, 5-ALA assisted in identifying the meningioma tissue as well as infiltrative disease in the dura and bone flap. In the same setting, 5-ALA fluorescence in adjacent nonneoplastic tissue, specifically after brachytherapy seed placement, was shown to be robust and nonspecific. Both observations set the stage for the further investigation of 5-ALA use in meningioma surgery and the implications for 5-ALA after brachytherapy.

Author Contributions

Conception and design: Choi, Ramapriyan, Clark, Curry, Carter. Acquisition of data: Choi, Ramapriyan, Clark, Martinez-Lage, Hsueh, Carter. Analysis and interpretation of data: Choi, Ramapriyan, Martinez-Lage, Curry, Carter. Drafting the article: Choi, Ramapriyan. Critically revising the article: Choi, Ramapriyan, Martinez-Lage, Curry, Carter. Reviewed submitted version of manuscript: Choi, Ramapriyan, Martinez-Lage, Hsueh, Nahed, Curry, Carter. Approved the final version of the manuscript on behalf of all authors: Choi. Administrative/technical/material support: Choi, Carter. Study supervision: Choi, Carter.