推荐回答(1个)
[病因病理]
星形细胞胶质瘤是颅内最常见的肿瘤,约占胶质瘤的80%,起源于星形神经胶质。成人多见于幕上,儿童多见于小脑。通常有两种分类法:一种为三分法,即低分级星形细胞瘤、间变性星形细胞瘤、多形性胶质母细胞瘤;另一种为四分法,即星形细胞瘤Ⅰ-Ⅳ级。Ⅰ-Ⅱ级相当于低分级星形细胞瘤、Ⅲ级相当于间变性星形细胞瘤,Ⅳ级即为胶质母细胞瘤。
低分级星形细胞瘤好发于年轻人的脑白质,肿瘤呈灶性或弥漫性浸润,常有囊腔形成,可为肿瘤内有囊或为囊内有肿瘤结节。质地较均匀,出血、坏死罕见,常无新生血管,15%-20%瘤内有钙化,瘤周无水肿。
Ⅲ-Ⅳ级星形细胞瘤呈弥漫浸润生长,轮廓不整,与脑质分界不清。半数以上有囊变。肿瘤易发生大片坏死和出血。肿瘤细胞分化程度不同,血管形成不良,毛细血管内皮细胞结合稀松。
[临床表现]
可发生任何年龄,以20-40岁多见,其临床症状、体征随肿瘤分级和部位不同而异。常见有颅内压增高和一般症状,有头痛、呕吐、视力减退、复视、癫痫发作和精神症状,还有因脑组织受压、浸润或破坏所产生的局部神经功能缺失症状。
[影像学表现]
1.CT表现:
①平扫:Ⅰ级星形细胞瘤表现为颅内低密度病灶,与脑质分界较清。占位表现不明显,仅有邻近脑室局部轻微受压和/或中线结构轻度向对侧移位。Ⅱ、Ⅲ级者表现为略高密度、混杂密度病灶或囊性肿块,可有点状钙化和肿瘤内出血,与脑质分界不清,形态不规则。占位表现及周围水肿均较显著。Ⅳ级则显示为略高或混杂密度病灶,边缘不规则,占位表现及脑水肿可更为明显。
②增强:Ⅰ级星形细胞瘤由于肿瘤血管内皮细胞结合紧密、没有或仅有少量造影剂血管外溢,故无强化或仅轻度强化。Ⅱ、Ⅲ级肿瘤因肿瘤血管形成不良,造影剂易发生血管外溢,故有明显强化。形态与厚度不一,在环壁上有时出现一强化的肿瘤结节,是星形细胞瘤的特征。有时可呈边界不清或清楚的弥漫性或结节性强化。Ⅳ级则较Ⅱ、Ⅲ级强化更明显,形态更不规则。
2.MR表现:
(1)I级星形细胞瘤:
①病灶位于皮髓质交界处,较表浅,局部脑沟变平。
②边缘不甚清晰,但信号强度均匀。T1加权为略低信号,T2加权为高信号。无增强效应。
③周围无水肿。
(2)Ⅱ级星形细胞瘤:
①病灶信号强度不甚均匀,有小囊性变。
②边缘有轻至中度水肿。
③增强后出现斑状、带状、连续或不连续的强化。
(3)Ⅲ、Ⅳ级级星形细胞瘤:
①病灶信号强度明显不均匀,多见囊变、出血。
②占位效应及水肿明显,边缘凹凸不整。
③增强检查为不均匀的明显强化;邻近病变的脑膜可因浸润而肥厚。
[鉴别诊断]
①少突胶质细胞瘤:瘤内钙化是少突胶质细胞瘤的特点之一,其钙化率达50%-80%,形态上为点状,或为斑点状,或为曲条状,后者在少突胶质细胞瘤的诊断上有一定的特征性,此外,少突胶质细胞瘤的瘤体常较大,而瘤周水肿相对较轻,不到肿瘤的1/3。但钙化亦见于星形细胞瘤,且其发病率高于少突胶质细胞瘤,故当大脑皮质下区显示含钙化的结节或肿块时,通常应首先考虑星形细胞瘤。
②血管畸形:畸形的血管反复出血后,有含铁血黄素沉积及钙化,可表现为不均匀密度的结节,但病变周围不应有明显水肿,亦无占位效应,除非有急性出血。
另外不同级别的星形细胞瘤还需与脑软化灶、脑脓肿、脑穿通畸形囊肿、脑膜瘤、脑转移瘤等鉴别。
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