Matyja E, Grajkowska W, Stępień K, Naganska E
Ewa Matyja, MD, PhD, Department of Experimental and Clinical Neuropathology, Mossakowski Medical Research Centre, Polish Academy of Sciences, 5 Pawinskiego St., 02-106 Warsaw, Poland, phone/fax: +48 22 668 55 32, e-mail:
Folia Neuropathol. 2016;54(3):197-211. doi: 10.5114/fn.2016.62530.
Pilocytic astrocytomas (PAs) are the most frequent primary astroglial tumours affecting children and adolescents. They occur sporadically or in association with a genetically determined syndrome - neurofibromatosis type 1. Classic PA usually manifests as a well-circumscribed, often cystic, slowly growing tumour, which corresponds to WHO grade I. The majority of pilocytic tumours arise along the neuraxis, predominantly in the cerebellum. They are associated with favourable long-term outcome or spontaneous regression, even after incomplete resection. However, the behaviour and prognosis might also be related to tumour histology and location. Pilomyxoid astrocytoma (PMA) represents a variant of classical PA with more invasive growth and increased risk of recurrences and dissemination. Typically, PAs exhibit distinct histology with biphasic architecture of loose, microcystic and compact, fibrillary areas. However, some tumours arise in an uncommon location and display heterogeneous histopathological appearance. The morphological pattern of PA can mimic some other glial neoplasms, including oligodendroglioma, pleomorphic xanthoastrocytoma, ependymoma or diffuse astrocytoma. Not infrequently, the advanced degenerative changes, including vascular fibrosis, and recent and old haemorrhages, may mimic vascular pathology. Sometimes, the neoplastic piloid tissue can resemble reactive gliosis, related to long-standing non neoplastic lesions. Not infrequently, PA exhibits histological features typical for anaplasia, including necrosis, mitoses and glomeruloid vascular proliferation that can suggest a diffuse high-grade glioma. However, even those PAs that lack distinct histological features of anaplasia can behave unpredictably, in a more aggressive manner, with leptomeningeal spreading. Genetic alterations resulting in aberrant signalling of the mitogen-activated protein kinase (MAPK) pathway have been considered to underlie the development of PAs. The most commonly identified KIAA1549-BRAF fusion is important for appropriate tumour molecular diagnosis. In this paper we summarize the clinicopathological presentation of PAs, with emphasis on their heterogeneous morphology, based on our own experience in the field of surgical neuropathology and the literature data. Diagnosis of pilocytic tumours requires careful analysis of clinical, histopathological and molecular features to avoid misinterpretation of these benign neoplastic lesions.
毛细胞型星形细胞瘤（PAs）是影响儿童和青少年的最常见的原发性星形胶质细胞瘤。它们散发性发生或与一种基因决定的综合征——1型神经纤维瘤病相关。典型的PA通常表现为边界清楚、常为囊性、生长缓慢的肿瘤，相当于世界卫生组织（WHO）I级。大多数毛细胞型肿瘤沿神经轴发生，主要位于小脑。即使在不完全切除后，它们也具有良好的长期预后或自发消退。然而，其行为和预后也可能与肿瘤组织学和位置有关。毛黏液样星形细胞瘤（PMA）是经典PA的一种变体，具有更强的侵袭性生长以及更高的复发和播散风险。通常，PA表现出独特的组织学特征，具有疏松、微囊性区域和致密、纤维状区域的双相结构。然而，一些肿瘤发生在不常见的位置，并表现出异质性的组织病理学外观。PA的形态学模式可模仿其他一些神经胶质肿瘤，包括少突胶质细胞瘤、多形性黄色星形细胞瘤、室管膜瘤或弥漫性星形细胞瘤。血管纤维化以及近期和陈旧性出血等晚期退行性改变并不少见，可能会模仿血管病变。有时，肿瘤性毛细胞样组织可能类似于与长期非肿瘤性病变相关的反应性胶质增生。PA并不少见地表现出间变的典型组织学特征，包括坏死、有丝分裂和肾小球样血管增生，这可能提示弥漫性高级别胶质瘤。然而，即使是那些缺乏明显间变组织学特征的PA，也可能表现出不可预测的、更具侵袭性的行为，并伴有软脑膜播散。导致丝裂原活化蛋白激酶（MAPK）途径异常信号传导的基因改变被认为是PA发生的基础。最常见的KIAA1549-BRAF融合对于适当的肿瘤分子诊断很重要。在本文中，我们根据自己在手术神经病理学领域的经验和文献数据，总结了PA的临床病理表现，重点是其异质性形态。毛细胞型肿瘤的诊断需要仔细分析临床、组织病理学和分子特征，以避免对这些良性肿瘤性病变的错误解读。
