Pilocytic astrocytomas

Abstract

Pilocytic astrocytoma (PA) is a well circumscribed neoplasm compared to diffuse astrocytoma. It is generally encountered under the age of 20 with a peak incidence between the ages 8 and 13. With respect to incidence, localization is as follows: cerebellum, optic nerve, optic chiasm, third ventricle region, spinal cord and temporal lobe. It arises as an exophytic mass at the dorsal part of the pons. It may be associated with neuorfibromatosis (NF) type I. Allelic loss is noticed at chromosome 17q in the sporadic cases. When compared with diffuse astrocytomas, TP 53 mutation is very low in these tumors. Gross features of pilocytic astrocytoma differ in various localizations. Histologically it is characterized by biphasic tissue pattern. “Rosenthal” fibres, eosinophilic granular bodies and hyalinization of vessels may be observed. Cellular pleomorphism, nuclear hyperchromasia, vascular proliferation, meningeal extension and the presence of necrosis are not indicators of anaplasia. In pilocytic astrocytoma the feature of anaplasia (malignancy) is considerable increase of mitoses. Treatment is total surgical excision. For midline tumors which cannot be removed surgically, radiotherapy may be applied. In children under the age of five with tumors of hypothalamus and optic tract, chemotherapy may be administered till the end of age five in order to protect the child from the traumatic effects of surgery and radiotherapy. Pilocytic astrocytoma is a benign, slow growing neoplasm with a long clinical history. Survival without recurrences may be over 20 years. Malignant recurrence may be rarely encountered (Anaplastic PA, WHO Grade III)

Keywords

• Pilocytic astrocytoma, Rosenthal fibres, biphasic patern

Pilositik astrositom

Öz

Pilositik astrositom (PA) diffuz astrositom ile karşılaştırıldığında iyi sınırlı bir neoplazmdır. Genellikle 20 yaşın altında görülür, 8-13 yaşları arasında pik yapar. Lokalizasyon, serebellum, optik sinir, optik kiazma, hipotalamus, üçüncü ventrikül bölgesi, spinal kord ve temporal lob olarak sıklık sırasına göre sıralanabilir. Ponsun dorsal bölümünde ekzofitik gelişir. Nörofibromatozis (N.F) tip I ile birlikte görülebilir. Sporadik olanların %20’sinde 17 q kromozomda allelik kayıp görülür. Bu tümörlerde diffüz astrositomlardan farklı olarak TP 53 mutasyonu çok azdır. Pilositik astrositomun makroskopik özellikleri farklı lokalizasyonlarda, farklılık gösterir. Histolojik olarak; bifazik doku paterni ile karakterizedir. “Rosenthal” fibrilleri, eozinofilik granüler cisimcikler ve damarlarda hiyalinizasyon görülebilir. Hücresel pleomorfizm, nükleer hiperkromazi, vasküler proliferasyon, meningial yayılım ve nekrozun bulunuşu anaplazi belirtisi değildir. Pilositik astrositomda anaplazi (malignite) bulgusu, mitozun anlamlı artışıdır. Sağaltım, total cerrahi rezeksiyondur. Cerrahi olarak çıkarılamıyan orta hat yerleşimli tümörlerde radyoterapi uygulanabilir. 5 yaşın altındaki çocuklarda hipotalamus ve optik traktüs lokalizasyonlu tümörlerde, 5 yaşın sonuna kadar, çocuğu cerrahi tedavi ve RT’nin travmatik etkisinden korumak için kemoterapi kullanılabilir. Pilositik astrositom, benign, yavaş büyüyen, klinik öyküsü uzun olan bir tümördür. Rekürrensiz survi 20 yılın üzerinde olabilir. PA’da seyrek olarak malign rekürrens görülebilir (Anaplastik PA, WHO Grade III)

Anahtar Kelimeler

• Pilositik astrositom, Rosenthal fibrilleri, bifazik görünüm

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