Role of the Apparent Diffusion Coefficient as a Predictor of Tumor Progression in Patients with Chordoma

Microstructural parameters from DW-MRI for tumour characterization and local recurrence prediction in particle therapy of skull-base chordoma

BACKGROUND

Quantitative imaging such as Diffusion-Weighted MRI (DW-MRI) can be exploited to non-invasively derive patient-specific tumor microstructure information for tumor characterization and local recurrence risk prediction in radiotherapy.

PURPOSE

To characterize tumor microstructure according to proliferative capacity and predict local recurrence through microstructural markers derived from pre-treatment conventional DW-MRI, in skull-base chordoma (SBC) patients treated with proton (PT) and carbon ion (CIRT) radiotherapy.

METHODS

Forty-eight patients affected by SBC, who underwent conventional DW-MRI before treatment and were enrolled for CIRT (n = 25) or PT (n = 23), were retrospectively selected. Clinically verified local recurrence information (LR) and histological information (Ki-67, proliferation index) were collected. Apparent diffusion coefficient (ADC) maps were calculated from pre-treatment DW-MRI and, from these, a set of microstructural parameters (cellular radius R, volume fraction vf, diffusion D) were derived by applying a fine-tuning procedure to a framework employing Monte Carlo simulations on synthetic cell substrates. In addition, apparent cellularity (ρ_app ) was estimated from vf and R for an easier clinical interpretation. Histogram-based metrics (mean, median, variance, entropy) from estimated parameters were considered to investigate differences (Mann-Whitney U-test, α = 0.05) in estimated tumor microstructure in SBCs characterized by low or high cell proliferation (Ki-67). Recurrence-free survival analyses were also performed to assess the ability of the microstructural parameters to stratify patients according to the risk of local recurrence (Kaplan-Meier curves, log-rank test α = 0.05).

RESULTS

Refined microstructural markers revealed optimal capabilities in discriminating patients according to cell proliferation, achieving best results with mean values (p-values were 0.0383, 0.0284, 0.0284, 0.0468, and 0.0088 for ADC, R, vf, D, and ρ_app, respectively). Recurrence-free survival analyses showed significant differences between populations at high and low risk of local recurrence as stratified by entropy values of estimated microstructural parameters (p = 0.0110).

CONCLUSION

Patient-specific microstructural information was non-invasively derived providing potentially useful tools for SBC treatment personalization and optimization in particle therapy.

Magnetic resonance imaging signal characteristics associated with prognosis of skull base chordoma after gamma knife radiosurgery

OBJECTIVE

To investigate the association between the magnetic resonance imaging (MRI) signal characteristics of skull base chordoma and radiosurgical outcomes.

METHODS

Twenty-four patients with skull base chordomas treated with Gamma Knife radiosurgery (GKRS) after previous surgical resection were retrospectively (2001-2021) examined. Pre-GKRS MRIs were analyzed for R_T2 (tumor-to-brainstem signal intensity ratio on T2-weighted imaging), R_CE (tumor-to-brainstem signal intensity ratio on contrast-enhanced T1-weighted imaging), and mean apparent diffusion coefficient (ADC). Correlations of the parameters with patient survival and local tumor progression were made by using Cox regression and Kaplan-Meier analyses.

RESULTS

During a median follow-up of 46 months after GKRS, 9 patients died with significantly more local tumor progression events (median number: 2 vs 0, P = .012) than did 15 alive patients. On multivariable analysis, higher mean ADC was associated with longer patient survival (P = .016) after GKRS. The actuarial 5-year overall survival rates were 88.9% versus 54.7% for chordomas with an ADC of ≥ 1270 × 10^-6 mm²/s versus < 1270 × 10^-6 mm²/s. R_T2 < 1.5 (P = .038) and R_CE > 1.57 (P = .022) were associated with a lower probability of local tumor control.

CONCLUSION

Lower mean ADC values are associated with shorter patient survival in skull base chordomas after GKRS. Diffusion-weighted imaging may help in GKRS planning and outcome prediction for these patients.

A practical overview of CT and MRI features of developmental, inflammatory, and neoplastic lesions of the sphenoid body and clivus

The sphenoid bone is an unpaired bone that contributes to the formation of the skull base. Despite the enormous progress in transnasal endoscopic visualisation, imaging techniques remain the cornerstones to characterise any pathological condition arising in this area. In the present review, we offer a bird’s-eye view of the developmental, inflammatory, and neoplastic alterations affecting the sphenoid body and clivus, with the aim to propose a practical diagnostic aid for radiologists based on clinico-epidemiological, computed tomography, and magnetic resonance imaging features.

New and Advanced Magnetic Resonance Imaging Diagnostic Imaging Techniques in the Evaluation of Cranial Nerves and the Skull Base

The skull base and cranial nerves are technically challenging to evaluate using magnetic resonance (MR) imaging, owing to a combination of anatomic complexity and artifacts. However, improvements in hardware, software and sequence development seek to address these challenges. This section will discuss cranial nerve imaging, with particular attention to the techniques, applications and limitations of MR neurography, diffusion tensor imaging and tractography. Advanced MR imaging techniques for skull base pathology will also be discussed, including diffusion-weighted imaging, perfusion and permeability imaging, with a particular focus on practical applications.

[Spinal neoplasms]

Spinal neoplasms are generally rare disorders but play an important role in the differential diagnosis of space-occupying masses of the spinal axis. Although there are several different classification criteria (histological origin, dignity, positional relationship to the spine), the standard classification of spinal neoplasms based on the relationship to the dura mater into extraspinal, intraspinal extramedullary and intraspinal intramedullary is used. Magnetic resonance imaging is the gold standard for the morphological imaging of spinal neoplasms, followed by computed tomography. In addition to localization and symptoms, the patient's age is essential with respect to the diagnosis of the possible tumor entity.

Central Skull Base Anatomy and Pathology: A Review

The central skull base is an anatomically complex region of the head and neck which hosts a variety of neoplastic, vascular, infectious, inflammatory, and developmental pathologies. Evaluation of its intricate anatomy requires dedicated and complementary imaging modalities of MRI and CT. This article will provide a brief review of the anatomy of the central skull base, followed by an overview of common pathologies encountered in this region and their characteristic radiological characteristics.

Apparent diffusion coefficient as a prognostic factor in clival chordoma

Clival chordoma is a rare disease with high recurrence rates even after a combination of surgical resection and radiotherapy. Apparent diffusion coefficient (ADC) has been used to evaluate aggressive features of chordoma, but its utility for clival chordoma has not been explored specifically. In this study, the utility of preoperative ADC values was analyzed for predicting tumor progression and recurrence in patients with clival chordoma. Between 2012 and 2019, a total of 30 operated cases were analyzed with available preoperative ADC data. Receiver operating characteristic (ROC) analysis was used to obtain ADC cutoff values for predicting tumor aggressiveness. The mean and minimum ADC values were significantly lower in the aggressive tumor group than in the stable tumor group (both P < 0.001). ROC analysis showed that a mean cutoff ADC value of 1198 × 10⁻⁶ mm²/s and minimum ADC value of 895.5 × 10^–6 mm²/s could be used to predict aggressive features of clival chordoma. Subtotal resection, partial resection, and mean and minimum ADC values that were lower than cutoff values were negative predictors of overall survival and progression-free survival. In conclusion, mean and minimum ADC values could be useful in predicting aggressiveness of clival chordoma.

Exophytic Lumbar Vertebral Body Mass in an Adult with Back Pain

Chordomas are rare primary bone malignancies derived from notochord remnants. The tumors often are slow-growing and often present with indolent, nonspecific symptoms. Nevertheless, chordomas are locally aggressive and highly prone to local recurrence, necessitating precise planning before biopsy and/or surgical resection. Familiarity with the imaging features of chordomas is, therefore, essential. This case highlights the typical imaging and pathologic features of a spinal chordoma as well as the surgical approach and the patient's subsequent outcome.

MRI Signal Intensity and Electron Ultrastructure Classification Predict the Long-Term Outcome of Skull Base Chordomas

BACKGROUND AND PURPOSE

MR imaging is a useful and widely used evaluation for chordomas. Prior studies have classified chordomas into cell-dense type and matrix-rich type according to the ultrastructural features. However, the relationship between the MR imaging signal intensity and ultrastructural classification is unknown. We hypothesized that MR imaging signal intensity may predict both tumor ultrastructural classification and prognosis.

MATERIALS AND METHODS

Seventy-nine patients with skull base chordomas who underwent 95 operations were included in this retrospective single-center series. Preoperative tumor-to-pons MR imaging signal intensity ratios were calculated and designated as ratio on T1 FLAIR sequence (R_T1), ratio on T2 sequence (R_T2), and ratio on enhanced T1 FLAIR sequence (R_EN), respectively. We assessed the relationships among signal intensity ratios, ultrastructural classification, and survival.

RESULTS

Compared with the matrix-rich type group, the cell-dense type chordomas showed lower R_T2 (cell-dense type: 1.90 ± 0.38; matrix-rich type: 2.61 ± 0.60 P < .001). The model of predicting cell-dense type based on R_T2 had an area under the curve of 0.83 (95% CI, 0.75-0.92). In patients without radiation therapy, both progression-free survival (P = .003) and overall survival (P = .002) were longer in the matrix-rich type group than in the cell-dense type group. R_EN was a risk factor for progression-free survival (hazard ratio = 10.24; 95% CI, 1.73-60.79); R_T2 was a protective factor for overall survival (hazard ratio  = 0.33; 95% CI, 0.12-0.87); and R_EN was a risk factor for overall survival (hazard ratio = 4.76; 95% CI, 1.51-15.01).

CONCLUSIONS

The difference in MR imaging signal intensity in chordomas can be explained by electron microscopic features. Both signal intensity ratios and electron microscopic features may be prognostic factors.

Monitoring Physiological Changes in Neutron-Exposed Normal Mouse Brain Using FDG-PET and DW-MRI

We monitored a physiological response in a neutron-exposed normal mouse brain using two imaging tools, [¹⁸F]fluro-deoxy-D-glucose positron emission tomography ([¹⁸F]FDG-PET) and diffusion weighted-magnetic resonance imaging (DW-MRI), as an imaging biomarker. We measured the apparent diffusion coefficient (ADC) of DW-MRI and standardized uptake value (SUV) of [¹⁸F]FDG-PET, which indicated changes in the cellular environment for neutron irradiation. This approach was sensitive enough to detect cell changes that were not confirmed in hematoxylin and eosin (H&E) results. Glucose transporters (GLUT) 1 and 3, indicators of the GLUT capacity of the brain, were significantly decreased after neutron irradiation, demonstrating that the change in blood-brain-barrier (BBB) permeability affects the GLUT, with changes in both SUV and ADC values. These results demonstrate that combined imaging of the same object can be used as a quantitative indicator for in vivo pathological changes. In particular, the radiation exposure assessment of combined imaging, with specific integrated functions of [¹⁸F]FDG-PET and MRI, can be employed repeatedly for noninvasive analysis performed in clinical practice. Additionally, this study demonstrated a novel approach to assess the extent of damage to normal tissues as well as therapeutic effects on tumors.