Intracranial SFT/HPC originates from Zimmerman cells in meningeal interstitial capillaries and accounts for about 1% of intracranial tumors [12, 21]. The 2016 World Health Organization classification of CNS tumors states that the pathological diagnostic criteria for grade intracranial III SFT/HPC is mitotic activity of at least 5/10 HPF, tumor necrosis, hemorrhage, and moderate to high cell density [1]. This means that the Ki-67 proliferation index of grade III SFT/HPC tumor entities is often ≥ 10% [16, 22, 23]. Furthermore, compared with grade II intracranial SFT/HPC, grade III SFT/HPC is associated with high postoperative recurrence, high metastasis, and low overall survival [4, 14, 24]. If the SFT/HPC grading can be clear before surgery, we can more accurately predict clinical postoperative tumor progression, which would allow surgeons to formulate more detailed treatment plans, including preoperative tumor interventions [25, 26], greater resection of the surrounding structure [4], and postoperative radiotherapy [27, 2]. However, it is still difficult for radiologists to effectively distinguish between grade II and grade III SFT/HPC before surgery. Previous studies have suggested that grade III SFT/HPC has certain MRI features, such as a narrow basement attached to the dura mater, increased necrosis/cystic degeneration, brain tissue edema, and heterogeneous enhancement [16, 17]. However, these features are subjective. In addition, these semantic features cannot be used to quantitatively analyze changes in the microstructure of intracranial SFT/HPC tumor entities. Therefore, more objective, quantitative parameters are still needed to effectively distinguish these two tumor grades, so as to effectively guide the implementation of clinical treatment measures.
To the best of our knowledge, this study is the first to focus on the use of the ADC for graded diagnosis of SFT/HPC. DWI can non-invasively evaluate the Brownian motion of water molecules in the tissue. The ADC is derived from DWI results and is mainly affected by the combined effect of the volume fractions inside and outside the cell. Therefore, the ADC can be of great significance for tumor grading, preoperative quantitative assessment, and differential diagnosis of brain tumors [3]. This study analyzed the ADCs of grade II and grade III SFT/HPC tumor entities and found that the MinADC, MeanADC, and rADC were significantly different in grade II and grade III SFT/HPC. The rADC had the highest accuracy in distinguishing grade II and grade III SFT/HPC (area under the curve = 0.897), with a diagnostic sensitivity and specificity of 80% and 95.5%, respectively. Chen et al [5]. found that the standardized ADC is of great significance in distinguishing SFT/HPC from meningioma. When the threshold of the standardized ADC is greater than 1.15, the sensitivity and specificity for distinguishing these two malignancies are 75% and 60.42%, respectively. Although they did not perform subgroup analysis of grades II and III intracranial SFT/HPC, they concluded that the ADC was negatively correlated with tumor malignancy and positively correlated with the extracellular space. Tumor cells in grade III SFT/HPC have increased mitotic activity and an enlarged nucleus and cytoplasm, resulting in the shrinkage of the space around the cells. This restricts the diffusion of water molecules, which decreases the ADC [3, 6]. Therefore, the ADC can reflect changes in the microstructure of tissues. Horvat et al [7]. found that the ADC of tumors can be used to differentiate molecular subtypes of invasive breast cancer. The maximum ADC has the highest diagnostic efficiency, which means that assessing the ADC before surgery can help doctors predict tumor grade and patient prognosis. The results of this study support the conclusions of previous studies showing that the ADC can non-invasively achieve tumor grading and typing, thereby assisting in the development of personalized treatment plans before surgery.
Histopathology can accurately distinguish grade II and III intracranial SFT/HPC based on tumor microstructure and cell morphology. The Ki-67 proliferation index is an important indicator that indirectly reflects the degree of tumor malignancy. Previous studies have shown that a higher Ki-67 proliferation index is correlated with an increased probability of tumor progression [4, 8, 9]. Multiple studies have shown that there is a correlation between the Ki-67 proliferation index of solid tumors and the ADC. Xianwang et al [10]. found a strong negative correlation between the MinADC and the Ki-67 proliferation index in ependymoma. He et al [20]. found that the MinADC and the Ki-67 proliferation index have a slight negative correlation in SFT/HPC, which is consistent with the results of this study. This negative correlation may be due to differences in cell cycle progression. Smaller cells are in G1 phase and larger cells are in G2/M phase, and as the cell volume increases, the extracellular volume decreases and the ADC decreases. The Ki-67 proliferation index is related to cell proliferation, and high expression of Ki-67 is observed in the G2/M phase. As the mitotic activity of the cell intensifies, the ADC gradually decreases and Ki-67 gradually increases, which leads to this negative correlation [11, 13]. This study found that the MeanADC, MinADC, and rADC had a strong negative correlation with the Ki-67 proliferation index in SFT/HPC. Because this tumor microstructure causes macroscopic differences in the ADC, the preoperative ADC predicts the Ki-67 proliferation index of intracranial SFT/HPC tumors. Therefore, the ADC is a preoperative, non-invasive factor that can assist surgeons in developing a detailed surgical plan and follow-up program.
This study had several limitations. First, this study took place in a single center and had a small sample size. In addition, because grade III SFT/HPC has more indicative radiological features than grade II SFT/HPC, such as necrosis, obvious cerebral edema, and heterogeneous enhancement, this may cause a certain subjective deviation in the manual measurement of the ADC. Finally, there is a lack of complete follow-up data, and the value of the ADC in the preoperative differentiation of grade II and III intracranial SFT/HPC needs further verification.