IDH-mutant Astrocytoma Arising in the Brainstem with Symptom Improvement by Foramen Magnum Decompression: A Case Report

Astrocytomas IDH-mutant of posterior cranial fossa, clinical presentation, imaging features and onco-functional balance in surgical management

IDH-mutant astrocytomas (AIDHmut) in the posterior cranial fossa (PCF) are rare and present substantial diagnostic and therapeutic challenges due to their location. We analyzed patients with PCF AIDHmut from our institutions, treated between December 2021 and September 2024. Additionally, we conducted a systematic literature review (from January 2021 to September 2024) using PubMed, Ovid MEDLINE, and Ovid EMBASE to identify cases of PCF AIDHmut. We identified a total of 19 cases, including one institutional case. Most patients were young adults, with a male predominance (15 males, 4 females). Tumors primarily originated from the brainstem (94.7%), with only one case involving the cerebellum. Clinical presentations frequently included cranial nerve deficits, with diplopia being the most common symptom (47.4%). Adjuvant radiotherapy (IMRT, DT 54 Gy/27 fractions, 78.9%) and chemotherapy (temozolomide, 68.4%) formed the mainstays of treatment. Tumor grading revealed 63.2% (12/19) were WHO grade 2, 21% (4/19) were WHO grade 3, and 15.8% (3/19) were grade 4. The mean follow-up period was 45 months. PCF AIDHmut are rare but pose significant treatment challenges due to their location and infiltrative nature. Multimodal treatment-comprising surgery, radiotherapy, and chemotherapy-is essential for achieving long-term disease control. Subtotal resection followed by adjuvant therapies provides a favorable balance between tumor control and functional preservation.

Clinical outcome, radiological findings, and genetic features of IDH-mutant brainstem glioma in adults

BACKGROUND

With the recent advent of genetic testing, IDH-mutant glioma has been found among adult brainstem gliomas. However, the clinical outcome and prognosis of IDH-mutant brainstem gliomas in adults have not been elucidated. This study aimed to investigate the clinical outcome, radiological findings, and genetic features of adult patients with IDH-mutant diffuse brainstem gliomas.

METHODS

Data from adult patients with brainstem glioma at Hokkaido University Hospital between 2006 and 2022 were retrospectively analyzed. Patient characteristics, treatment methods, genetic features, and prognosis were evaluated.

RESULTS

Of 12 patients with brainstem glioma with proven histopathology, 4 were identified with IDH mutation. All patients underwent local radiotherapy with 54 Gray in 27 fractions combined with chemotherapy with temozolomide. Three patients had IDH1 R132H mutation and one had IDH2 R172G mutation. The median progression-free survival and overall survival were 68.4 months and 85.2 months, respectively, longer than that for IDH-wildtype gliomas (5.6 months and 12.0 months, respectively). At the time of initial onset, contrast-enhanced lesions were observed in two of the four cases in magnetic resonance imaging.

CONCLUSION

As some adult brainstem gliomas have IDH mutations, and a clearly different prognosis from those with IDH-wildtype, biopsies are proactively considered to confirm the genotype.

Patterns of T2-FLAIR discordance across a cohort of adult-type diffuse gliomas and deviations from the classic T2-FLAIR mismatch sign

PURPOSE

T2-FLAIR mismatch serves as a highly specific but insensitive marker for IDH-mutant (IDHm) astrocytoma with potential limitations in real-world application. We aimed to assess the utility of a broader definition of T2-FLAIR discordance across a cohort of adult-type diffuse lower-grade gliomas (LrGG) to see if specific patterns emerge and additionally examine factors determining deviation from the classic T2-FLAIR mismatch sign.

METHODS

Preoperative MRIs of non-enhancing adult-type diffuse LrGGs were reviewed. Relevant demographic, molecular, and MRI data were compared across tumor subgroups.

RESULTS

Eighty cases satisfied the inclusion criteria. Highest discordance prevalence and > 50% T2-FLAIR discordance volume were noted with IDHm astrocytomas (P < 0.001), while < 25% discordance volume was associated with oligodendrogliomas (P = 0.03) and IDH-wildtype (IDHw) LrGG (P = 0.004). "T2-FLAIR matched pattern" was associated with IDHw LrGG (P < 0.001) and small or minimal areas of discordance with oligodendrogliomas (P = 0.03). Sensitivity and specificity of classic mismatch sign for IDHm astrocytoma were 25.7% and 100%, respectively (P = 0.06). Retained ATRX expression and/or non-canonical IDH mutation (n = 10) emerged as a significant factor associated with absence of classic T2-FLAIR mismatch sign in IDHm astrocytomas (100%, P = 0.02) and instead had minimal discordance or matched pattern (40%, P = 0.04).

CONCLUSION

T2-FLAIR discordance patterns in adult-type diffuse LrGGs exist on a diverging but distinct spectrum of classic mismatch to T2-FLAIR matched patterns. Specific molecular markers may play a role in deviations from classic mismatch sign.