TO THE EDITOR: We read with a great deal of interest the article by Lam et al.1 (Lam J, Tomaszewski P, Gilbert G, et al. The utility of arterial spin labeling in the presurgical evaluation of poorly defined focal epilepsy in children. J Neurosurg Pediatr. 2021;27[3]:243–252). The authors describe the results of an arterial spin labeling (ASL) study in 25 cases of poorly defined focal epilepsy in children. The paper was intelligently written, providing insights into the role of ASL in MRI-positive and MRI-negative cases in localizing the epileptogenic zone (EZ). ASL was done as part of an exhaustive presurgical evaluation along with MRI, video-electroencephalography, PET, ictal/interictal SPECT, magnetoencephalography, and invasive intracranial recordings. Microvessel density was studied in 12 specimens (8 were pathological and 4 were internal controls). In 11 patients who had undergone surgery, the EZ was proven by good seizure outcome and histopathology.
ASL abnormalities were 85% concordant with MRI, 75% with FDG-PET, and 62.5% with SPECT. Ten of the surgically treated patients were MRI positive, and ASL was concordant qualitatively and quantitatively. Only 1 MRI-negative patient was surgically treated, and in that patient perfusion abnormality was not seen in the qualitative assessment and retrospective quantitative analysis showed perfusion abnormality that was concordant with the EZ. Microvessel density in focal cortical dysplasia was not significantly different from that in internal controls.
Their prospective study is strengthened by comprehensive methodology, histopathology, and long-term seizure outcome. Although ASL perfusion abnormalities were well correlated in MRI-positive cases, ASL did not have a role in localizing the EZ. As the authors hypothesized, this could be a consequence of poor spatial resolution and signal-to-noise ratio.
We appreciate the authors for optimizing the imaging protocol, such as the 3D pseudocontinuous readout protocol to improve spatial resolution,2 post-label delay of 1500 msec3 in these pediatric patients, and quantitative analysis in all cases. Although the authors claim that the study compares the ability of ASL to localize the EZ in MRI-positive versus MRI-negative cases, we believe that the role of ASL in EZ localization in MRI-negative cases is limited, as only 1 MRI-negative case was surgically treated and had evidence of the EZ.
At present, ASL has limited value compared to FDG-PET and SPECT in MRI-negative cases because of poor spatial and temporal resolution and signal-to-noise ratio. FDG-PET and ictal/interictal subtraction SPECT are better correlated with the EZ.4 More prospective studies are required to establish the role of ASL in these difficult cases, especially MRI-negative cases.
Disclosures
The authors report no conflict of interest.
References
- 1↑
Lam J, Tomaszewski P, Gilbert G, et al. The utility of arterial spin labeling in the presurgical evaluation of poorly defined focal epilepsy in children. J Neurosurg Pediatr. 2021;27(3):243–252.
- 3↑
Hu Y, Li Q, Chen L, Lv F. Multidelay arterial spin-labeled perfusion magnetic resonance imaging in healthy individuals: a single-center experience. Neurol India. 2019;67(3):829–833.
- 4↑
Chandra PS, Vaghania G, Bal CS, et al. Role of concordance between ictal-subtracted SPECT and PET in predicting long-term outcomes after epilepsy surgery. Epilepsy Res. 2014;108(10):1782–1789.
