Posterior fossa tümörleri: medulloblastom, ependimom ve pilositik astrositom

Özet

Çocukluk çağında posterior fossa kitleleri dördüncü ventrikülü veya BOS çıkış yollarını daraltarak obstrüktif hidrosefaliyle ortaya çıkabilir. BT, pediatrik beyin tümörlerinin ön tanı ve karakterizasyonunda kitle yerleşimi, yoğunluk özellikleri ve çevre yapılar üzerine etkileri açısından değerli bir yöntemdir. Medulloblastom, ependimom ve pilositik astrositomun BT görünümleri örtüşür; tümör tipini belirlemek için MR ve doku tanısı gerekir. Dördüncü ventrikül basısı BOS akımını bozarak obstrüktif hidrosefaliye yol açabilir.

Faz ve pencere

Kontrastsız tanısal

Posterior fossa kitle atenüasyonu, kaba kalsifikasyon veya kanama, dördüncü ventrikülün yer değiştirmesi/dolması ve supratentoryal ventrikül genişlemesi incelenir. Posterior fossa artefaktları, özellikle beyin sapı ve derin serebellar lezyonların BT’de saptanmasını güçleştirebilir.

Önerilen pencereler: Beyin (G 80 / M 40), Kemik (G 1800 / M 400).

BT bulguları

• Serebellar vermis, hemisfer, dördüncü ventrikül veya beyin sapı merkezli kitle odağını belirle.
• Dördüncü ventrikülün öne itilmesi, genişlemesi ya da tümörle dolması kitle komşuluğunu gösterir.
• Akuadukt ve sisterna magna çevresindeki BOS boşluklarında silinme veya daralma ara.
• Medulloblastom, yüksek hücre yoğunluğuna bağlı olarak BT’de hiperdens görünebilir.
• Ependimom dördüncü ventrikül içinde şekillenen ve çıkış açıklıklarına uzanabilen heterojen bir kitle olabilir.
• Pilositik astrositom serebellar hemisferde kistik bileşen ve mural solid odakla görülebilir.
• Ventrikülomegali, transependimal ödem ve bazal sistern basısı obstrüktif hidrosefalinin eşlikçileri olabilir.

Normalde

Kitle tarafında dördüncü ventrikülün biçim ve konum değişikliği, çevre sisternlerin silinmesi ve lateral ventrikül genişlemesiyle kıyasla.

Ayırıcı tanı

Beyin sapı gliomu

ekspansil kitle pons merkezindedir; dördüncü ventrikül arkaya (posteriora) itilmiş veya basılanmış olabilir.

Atipik teratoid/rabdoid tümör

küçük çocukta heterojen posterior fossa kitlesi olarak medulloblastomu taklit edebilir.

Kontrastlı görüntülemede halka şeklinde kontrastlanma ve çevresinde ödem oluşturabilen enfeksiyonel bir lezyondur.

Serebellar hemoraji

akut kan yoğunluğu ve çevresinde ödem ile dördüncü ventrikülü basabilir.

Tuzaklar

• Posterior fossa artefaktları lezyon saptanmasını güçleştirebilir; beyin sapı ve derin serebellar bölgeleri dikkatle gözden geçir.
• Dördüncü ventrikül basısı tek başına tümör tipini ayırt ettirmez; kitle merkezi ve iç yapısı birlikte okunur.
• Kistik bileşen ve mural solid nodül pilositik astrositomu destekleyebilir ama özgül değildir; nodülün kontrastlanması kontrastlı MR'da değerlendirilir. Kontrastsız BT bulguları tümör tipine ilişkin ipuçları sağlar; farklı histolojik tümör tiplerini ayırt etmede MR ek bilgi ve tanısal güven sağlayabilir.

Kendini dene

1. Posterior fossa kitlesi ve ventriküler genişleme birlikte görüldüğünde hangi komplikasyon öncelikle düşünülmelidir?

   • Obstrüktif hidrosefali
   • Normal varyant
   • Serebellar atrofi
   • Venöz sinüs hipoplazisi
   Cevabı göster

   Obstrüktif hidrosefali. Posterior fossa kitleleri obstrüktif hidrosefaliye yol açabilir. İleri görüntüleme teknikleri histolojik ve moleküler alt grubu tahmin etmede yardımcı olur, ancak kesin tanı dokusal ve genetik analize dayanır.

2. Dördüncü ventrikül çevresinden başlayıp Luschka açıklıklarından komşu sisternalara uzanan kitle hangi tümörle daha uyumludur?

   • Ependimom
   • Pilositik astrositom
   • Medulloblastom
   • Koroid pleksus kisti
   Cevabı göster

   Ependimom. Ependimomlar çoğunlukla dördüncü ventrikül içinde veya yakınında gelişir ve Luschka açıklıklarından komşu sisternalara uzanabilir. Bu yerleşim tanısal ipucudur; tümör tipini belirlemek için MR değerlendirmesi önemlidir.

İlgili konular

• Pediatrik beyin tümörleri: BT’de kitle ve kalsifikasyon
• BOS şantı ve mekanik komplikasyonları

Kaynaklar

Bu sayfadaki 33 cümle ve 2 quiz sorusu aşağıdaki kaynaklardan alıntılarla otomatik olarak karşılaştırıldı; 11 cümle bu karşılaştırmada düzeltildi (2026-10-09).

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Eğitim amaçlıdır; hasta başında tanı ve tedavi kararının yerine geçmez, tıbbi tavsiye değildir. Metinler yapay zekâ desteğiyle yazıldı ve otomatik bir adımda kaynak alıntılarıyla karşılaştırıldı; bu bir tıbbi doğrulama değildir ve içerik uzman radyolog incelemesinden geçmedi. Klinik kararlarda güncel kılavuzları, kurum protokollerini ve radyoloji raporunu esas alın.