ASL Perfusion Lightbulb Sign: An Imaging Biomarker of Pediatric Posterior Fossa Hemangioblastoma.

BACKGROUND AND PURPOSE: Hemangioblastoma is a rare vascular tumor that occurs within the central nervous system in children. Differentiating hemangioblastoma from other posterior fossa tumors can be challenging on imaging, and preoperative diagnosis can change the neurosurgical approach. We hypothesize that a 'lightbulb sign' on the ASL sequence (diffuse homogenous intense hyperperfusion within the solid component of the tumor) will provide additional imaging finding to differentiate hemangioblastoma from other posterior fossa tumors. MATERIALS AND METHODS: In this retrospective comparative observational study, we only included pathology-proven cases of hemangioblastoma, while the control group consisted of other randomly selected pathology-proven posterior fossa tumors from January 2022 to January 2024. Two blinded neuroradiologists analyzed all applicable MRI sequences, including ASL sequence if available. ASL was analyzed for the 'lightbulb sign'. Disagreements between the radiologists were resolved by a third pediatric neuroradiologist. Chi-square and Fisher's exact test were used to analyze the data. RESULTS: 95 patients were enrolled in the study; 57 (60%) were male. The median age at diagnosis was 8 years old (IQR: 3-14). Out of the enrolled patients, 8 had hemangioblastoma, and 87 had other posterior fossa tumors, including medulloblastoma (n=31), pilocytic astrocytoma (n=23), posterior fossa ependymoma type A (n=16), and other tumors (n=17). The comparison of hemangioblastoma vs non-hemangioblastoma showed that peripheral edema (p=0.02) and T2 flow void (p=0.02) favors hemangioblastoma, whereas reduced diffusion (low ADC) (p=0.002) and ventricular system extension (p=0.001) favors nonhemangioblastoma tumors.Forty-two cases also had ASL perfusion sequences. While high perfusion favors hemangioblastoma (p=0.03), the lightbulb sign shows a complete distinction since all the ASL series of hemangioblastoma cases (n=4) showed the lightbulb sign, whereas none of the nonhemangioblastoma cases (n=38) showed the sign (p<0.001). CONCLUSIONS: Lightbulb-like intense and homogenous hyperperfusion patterns on ASL are helpful in diagnosing posterior fossa hemangioblastoma in children.ABBREVIATIONS ASL = Arterial spin labelling; pASL = Pulsed arterial spin labelling; pCASL = Pseudocontinuous arterial spin labelling; DCE = Dynamic contrast-enhanced; DSC = Dynamic susceptibility contrast; VHL = Von Hippel Lindau.

Differentiation between germinoma and other pineal region tumors using diffusion-and susceptibility-weighted MRI.

PURPOSE: To evaluate the effectiveness of diffusion-weighted imaging (DWI) and susceptibility-weighted imaging (SWI) for differentiation between germinoma and other pineal region tumors. METHOD: This retrospective study consisted of 72 patients with pathologically proven pineal region tumors between January 2010 and August 2020. Tumors were classified as germinomas (40), non-germinomatous germ cell tumors (11) (NGGCT), pineal parenchymal tumors (10) (PPT), and other types of tumors (11). Visual scale score, ADC values and SWI intratumoral susceptibility signal (ITSS) score were analyzed and compared to histopathology data. RESULTS: The mean apparent diffusion coefficient (ADCmean) and minimum apparent diffusion coefficient (ADCmin) ratio of germinoma were significantly lower than NGGCT. ADCmean or ADCmin cut-off ratio of ≤ 1.48 or ≤ 1.32 allowed for discrimination between germinoma and NGGCT with sensitivity and specificity of 100 % and 63.6 %. An ADCmin cut-off ratio of ≥ 0.93 allowed for discrimination between germinoma and PPT with sensitivity and specificity of 60 % and 80.0 %. ADCmin cut-off ratio of ≤ 1.15 allowed for discrimination of germinoma from other types of tumors with sensitivity and specificity of 87.5 % and 54.5 %. CONCLUSIONS: ADC ratio can differentiate germinoma from other types of pineal region tumors. Our initial results suggest that ITSS score was not significantly correlated with specific histology subtype.

Diffusion MRI in Evaluation of Pediatric Posterior Fossa Tumors.

BACKGROUND: To evaluate the role of diffusion MRI in differentiating pediatric posterior fossa tumors and determine the cut-off values of ADC ratio to distinguish medulloblastoma from other common tumors. METHODS: We retrospectively reviewed MRI of 90 patients (7.5-year median age) with pathologically proven posterior fossa tumors (24 medulloblastoma, 7 ependymoma, 4 anaplastic ependymoma, 13 pilocytic astrocytoma, 30 diffuse intrinsic pontine glioma (DIPG), 4 ATRT, 3 diffuse astrocytoma, 2 high grade astrocytoma, 2 glioblastoma, and 1 low grade glioma). The conventional MRI characteristics were evaluated. Two readers reviewed DWI visual scale and measured ADC values by consensus.  ADC measurement was performed at the solid component of tumors. ADC ratio between the tumors to cerebellar white matter were calculated. RESULTS: The ADC ratio of medulloblastoma was significantly lower than ependymoma, pilocytic astrocytoma and DIPG. The ADC cut-off ratio of ≤ 1.115 allowed discrimination medulloblastoma from other posterior fossa tumors with sensitivity, specificity, PPV and NPV of 95.8%, 81%, 67.6% and 97.9%, respectively. ADC ratio cut-off level to differentiate medulloblastoma from ependymoma was ≤ 0.995 with area under the curve (AUC)= 0.8693. ADC ratio cut-off level for differentiate medulloblastoma from pilocytic astrocytoma at ≤ 1.17 with AUC = 0.9936. ADC cut-off level for differentiate medulloblastoma from DIPG at ≤ 1.195 with AUC = 0.9681. The ADC ratio was correlated with WHO grading by the lower ADC ratio associated with the higher grade. Furthermore, High DWI visual scale was associated with high grade tumor. CONCLUSION: Diffusion MRI has a significant role in diagnosis of pediatric posterior fossa tumors. ADC ratio can be used to distinguish medulloblastoma from other posterior fossa tumor with good level of diagnostic performance.