A pilot study of lymphoscintigraphy with tracer injection into the human brain

Abstract

Many groups have reported lymphatic and glymphatic structures in animal and human brains, but tracer injection into the human brain to demonstrate real-time lymphatic drainage and mapping has not been described. We enrolled patients undergoing standard-of-care resection or stereotactic biopsy for suspected intracranial tumors. Patients received peritumoral injections of ^99mTc-tilmanocept followed by planar or tomographic imaging. Fourteen patients with suspected brain tumors were enrolled. One was excluded from analysis because of tracer leakage during injection. There was no drainage of ^99mTc-tilmanocept to regional lymph nodes in any of the patients. On average, after correcting for radioactive decay, 70.7% (95% CI: 59.9%, 81.6%) of the tracer in the injection site and 78.1% (95% CI: 71.1%, 85.1%) in the whole-head on the day of surgery remained the morning after, with variable radioactivity in the subarachnoid space. The retained fraction was much greater than expected based on the clearance rate from non-brain injection sites. In this pilot study, the lymphatic tracer ^99mTc-tilmanocept was injected into the brain parenchyma, and there was no drainage outside the brain to the cervical lymph nodes. Our work demonstrates an inefficiency of drainage from peritumoral brain parenchyma and highlights a therapeutic opportunity to improve immunosurveillance of the brain.

Keywords: Brain; glymphatics; lymphatics; neuroimmunology; tilmanocept.

Figure 1.

Planar and SPECT/CT images after ^99mTc-tilmanocept injection. (a) Planar images for each patient are shown from left to right: anterior day of surgery, anterior day after surgery, right lateral day of surgery, right lateral day after surgery. Patient 1: Female, 40 years old, right frontal lobe ^99mTc-tilmanocept injection, radiation gliosis without neoplasm; Patient 2: Male, 72 years old, right temporal lobe injection, lung metastasis; Patient 3: Male, 67 years old, right frontal lobe injection, anaplastic oligodendroglioma; Patient 4: Male, 48 years old, right parietal injection, glioblastoma; Patient 5: Female, 68 years old, right frontal lobe injection, lung metastasis; and Patient 6: Male, 21 years old, right frontal lobe injection, low grade astrocytoma. (b) Graph of raw counts per minute (not decay corrected) for all images (anterior and lateral) of patients 1–6, each line represents change in radioactivity in the whole head and (c) SPECT/CT axial, coronal, and sagittal images are shown for each patient. Patient 7: Male, 51 years old, right parietal lobe melanoma metastasis, 3.5 hr after injection; Patient 8: Female, 86 years old, right frontal lobe breast carcinoma metastasis, 5 hr after injection; Patient 9: Male, 64 years old, right parietal lobe glioblastoma, 18.5 hr after injection.

Figure 2.

Presence of CD206 in the brain. (a) Normal human tonsil (positive control, Novus Biologicals) stained with DAPI (blue) and anti-CD206 (magenta). (b) Glioblastoma tumor stained with DAPI (blue) and anti-CD206 (magenta). (c and d) Adjacent white matter stained with DAPI (blue) and anti-CD206 (magenta). (e) Tissue gene expression of MRC1 (normalized transcripts per million) from the Human Protein Atlas (mean nTPM for Cerebral Cortex: 0.669, White Matter 0.506, Breast: 16.3, Skin: 2.1, Lymph Node: 15.2, and Spleen: 50.6) and (f) Tissue sections stained for CD206 from the Human Protein Atlas.

Figure 3.

SPECT/CT axial, coronal, and sagittal images after resection or biopsy and ^99mTc-tilmanocept injection. Patient 10: Female, 40 years old, right frontal lobe meningioma, 20 hours after tumor resection and injection, a small amount of tracer is visible extracranially, likely in the subgaleal space; Patient 11: Female, 65 years old, right temporal meningioma, 4 hours after tumor resection and injection; Patient 12: Female, 54 years old, right frontotemporal meningioma, 16.25 hours after tumor resection and injection; Patient 13: Male, 65 years old, left occipital glioblastoma, 3.5 hours after stereotactic biopsy and injection.