毛细胞型星形细胞瘤(pilocytic astrocytoma,PA),属于神经上皮肿瘤中星形细胞起源肿瘤的亚型,是一种少见的良性肿瘤,由Penfield于1937年根据肿瘤细胞两端见细长的毛发样胶质纤维丝而命名。2007年和2016年版WHO中枢神经系统肿瘤组织学分类标准中均列为I级星形细胞肿瘤。
Pilocytic astrocytoma (PA), a subtype of astrocyte-derived neoplasms in neuroepithelial tumors, is a rare benign neoplasm. It was named by Penfield in 1937 for the presence of long hair-like glial filaments at both ends of the neoplastic cells. The WHO Central Nervous System Tumor Histological Classification Standards (2007 and 2016 editions) are classified as Grade I astrocytic tumors.
PA占颅内肿瘤的1.9%,约占原发性中枢神经系统肿瘤的1.5%,好发于儿童和青少年,多数在20岁之前发病,在4岁左右出现发病高峰,随年龄增长发病率有下降趋势,45岁以上成年人发病率不足1/100万,男女发病比率无明显差异。PA可起源于整个神经轴的任何位置,但好发于小脑视交叉、下丘脑、视神经等部位,也可以发生在脑干、大脑半球、基底节及脊髓,其中发生于视交叉、下丘脑、视神经的PA常伴有神经纤维瘤病1型( Neurofibromatosis1,NF1)。视路胶质瘤有两种存在形式,一种独立存在,另一种为NF1相关型,前者更为常见,后者约占视路胶质瘤的30%。NF相关型视路胶质瘤是NF1患者最常见的脑肿瘤,其发病率为15%-50%,发病高峰在2-8岁之间。脑干胶质瘤可简单地分为弥漫性浸润性胶质瘤和局灶性胶质瘤,而局灶性胶质瘤主要为PA,大多数儿童PA都位于幕下,特别是小脑(60%)
PA accounted for 1.9% of intracranial tumors and 1.5% of primary central nervous system tumors. Most of them occurred in children and adolescents before the age of 20 and peaked around the age of 4. The incidence of PA declined with age. The incidence rate of adults over 45 years old was less than 1/1 million. There was no significant difference between male and female. PA can originate from any part of the whole nerve axis, but it is predominant in cerebellum optic chiasm, hypothalamus, optic nerve, etc. It can also occur in brain stem, cerebral hemisphere, basal ganglia and spinal cord. PA occurring in optic chiasm, hypothalamus and optic nerve is often accompanied by neurofibromatosis type 1 (NF1). There are two types of glioma, one is independent and the other is NF1-related. The former is more common, and the latter accounts for about 30% of glioma. NF-related gliomas are the most common brain tumors in NF1 patients. The incidence of these tumors ranges from 15% to 50%. The peak incidence of these tumors is between 2 and 8 years old. Brainstem gliomas can be simply divided into diffuse invasive gliomas and focal gliomas, while focal gliomas are mainly PA, most of which are located under the tentorium, especially in the cerebellum (60%).
虽然PA是良性肿瘤,但其影像学表现因肿瘤位置不同而有所差异,在影像学上根据其生长方式可分为两种主要类型:单纯膨胀型和浸润型;单纯膨胀型指肿瘤位于小脑或大脑半球,浸润型PA通常起源于间脑或脑干,浸润型PA常呈实性肿块。
Although PA is a benign neoplasm, its imaging manifestations vary according to the location of the neoplasm. According to its growth pattern, PA can be divided into two main types: simple expansive type and invasive type. Simple expansive type refers to tumors located in the cerebellum or cerebral hemisphere. Invasive PA usually originates from the diencephalon or brainstem, and invasive PA often presents solid masses.
PA生长缓慢,一般预后良好,PA治疗首选显微外科手术,影响预后的重要因素是肿瘤的部位、手术切除程度。PA在儿童主要发生在小脑半球,10年生存率可达90%,而40岁以上患者10年生存率约70%。肿瘤全部切除术后5年无复发率可达95%,当肿瘤不能完全切除时,残留肿瘤进展、恶变比较罕见。近年来有研究发现部分PA残留部分随着时间推移不进展,甚至退化,这种消退机制可能与手术阻断了肿瘤血供或抑制了肿瘤生长因子分泌有关。
PA grows slowly and generally has a good prognosis. Microsurgery is the first choice for PA treatment. The important factors affecting the prognosis are the location of the tumor and the degree of surgical resection. PA mainly occurs in the cerebellar hemisphere in children. The 10-year survival rate can reach 90%, while the 10-year survival rate of patients over 40 years old is about 70%. Five years after total resection, the recurrence rate was 95%. When the tumor could not be completely resected, the residual tumor progression and malignancy were rare. In recent years, some studies have found that some PA residues do not progress or even degenerate over time. This regression mechanism may be related to blocking the blood supply of tumors or inhibiting the secretion of tumor growth factor.
病理大体可见大部分毛细胞星形细胞瘤质地较软,呈灰色。肿瘤病灶内部或肿瘤周围常可见囊性变。发生于脊髓者,可见脊髓空洞形成累及多个节段。病灶内可见钙化或含铁血黄素沉积。发生于视神经的肿瘤常如袖套样累及蛛网膜下腔。显微镜下显示轻-中度细胞分化的毛细胞星形细胞瘤具有致密区和疏松区的双相组织学特点,前者含有Rosenthal纤维的梭形细胞,后者主要由多极细胞组成,伴有微囊和嗜酸性颗粒小体/玻璃样小滴形成,罕见核分裂相。
Histologically, most pilocytic astrocytomas are soft and grey. Cystic changes are often seen in or around the tumors. In the spinal cord, the formation of syringomyelia involving multiple segments can be seen. Calcification or hemosiderin deposits can be seen in the lesion. Tumors arising from the optic nerve often involve the subarachnoid space as sleeves. Microscopically, mild-to-moderate differentiated hairy cell astrocytomas have biphasic histological features of dense and loose areas. The former contains spindle cells of Rosenthal fibers, while the latter consists mainly of multipolar cells, accompanied by microcapsules and eosinophilic granulosomes/vitreous droplets, with rare mitotic phase.
患者可出现局灶性神经功能障碍或巨颅症、头痛、内分泌紊乱、颅内压升高等非特异性体征,这是由肿瘤占位效应和脑室梗阻引起的。由于肿瘤较少累及大脑皮层,因此癫痫发作不常见。位于眶内的肿瘤可导致眼球外突,累及视路者可造成视野缺损,巨大的下丘脑肿瘤常可引起下丘脑/垂体功能障碍,出现肥胖、尿崩症等临床表现。
Focal neurological dysfunction or giant crania, headache, endocrine disorders, elevated intracranial pressure and other non-specific signs may occur in patients, which are caused by tumor space-occupying effect and ventricular obstruction. Epilepsy seizures are uncommon because tumors rarely involve the cerebral cortex. Tumors located in the orbit can lead to exophthalmos and visual field defect if they involve visual pathways. Giant hypothalamic tumors often cause hypothalamic/pituitary dysfunction, obesity, diabetes insipidus and other clinical manifestations.
CT：病变以囊性为主时呈低密度,囊实性时呈等、低密度,实性病变为等或稍低密度,边界清楚,肿瘤周围无水肿。
The main lesions were cystic lesions with low density, cystic and solid lesions with equal or slightly low density, clear margin and no edema around the tumors.
MRI：小脑毛细胞型星形细胞瘤多具有典型的影像学特点,即以囊性病变为主伴附壁结节。T1WI囊液呈均匀低信号,壁结节呈稍低于脑组织的低信号;T2WI囊液呈均匀高信号,壁结节呈稍高信号;T2-FLAIR像囊液呈低信号,壁结节呈高信号;增强扫描壁结节明显强化伴/不伴囊壁强化,囊液不强化。典型的PA通常无周围水肿。
Cerebellar pilocytic astrocytomas have typical imaging features, i. e. cystic lesions with mural nodules. T1WI cystic fluid showed uniform low signal, mural nodules showed slightly lower signal than brain tissue; T2WI cystic fluid showed uniform high signal, mural nodules showed slightly high signal; T2-FLAIR cystic fluid showed low signal, mural nodules showed high signal; mural nodules enhanced significantly with/without cystic wall enhancement, cystic fluid did not strengthen. Typical PA usually has no surrounding edema.
不典型PA影像学特点
①单纯囊肿型:表现为囊性,壁薄且内有囊性分隔,周围无水肿,囊壁T1WI呈等低信号,T2WI呈稍高信号,增强扫描囊壁和囊内分隔均见强化;
It was cystic with thin wall and cystic septation. There was no edema around the cyst. The cyst wall showed iso-low signal on T1WI and slightly high signal on T2WI.
②囊实型:实性部分中见囊变区;MR平扫实性部分T1WI呈低信号, T2WI呈稍高信号,增强扫描明显强化,囊性部分DWI呈低信号,增强扫描囊壁无强化;
Cystic degeneration was seen in solid part, low signal on T1WI and slightly high signal on T2WI on plain MR scan, and low signal on DWI on cystic part, but no enhancement on cystic wall on enhanced scan.
③实性型:病灶表现为不规则形或类圆形实性肿块,T1WI呈低信号,T2WI呈稍高信号,T2-FLAIR呈稍高信号,增强扫描肿块呈均匀团块状强化。
The lesions showed irregular or round solid masses, low signal on T1WI, slightly high signal on T2WI, slightly high signal on T2-FLAIR, and homogeneous mass enhancement on enhanced scan.
PA属于低级别肿瘤,实性部分却表现为明显强化,是因为PA自身包含有孔型毛细血管所致,对比剂通过孔道到达血管的内皮间隙,从而导致实性区域的明显强化,这与恶性肿瘤破坏血脑屏障导致对比剂聚集不同。
PA belongs to low-grade tumors, but the solid part of PA shows obvious enhancement, because PA itself contains porous capillaries. Contrast reaching the endothelial space of blood vessels through the channels, leading to obvious enhancement of solid areas, which is different from the aggregation of contrast agents caused by malignant tumors destroying blood-brain barrier.
MRS表现为Cho增高、NAA降低和Lac峰增高,在PA中出现Lac峰增高不一定是由肿瘤出现坏死所致,因为病理上PA内极少出现坏死,而可能与低级别肿瘤线粒体代谢的改变或葡萄糖的利用率变化有关。肿瘤组织DWI信号主要取决于瘤细胞核质比例,肿瘤细胞结构紧密会使水分子扩散受限,DWI信号则增高,ADC值减小。DWI主要表现为低信号,部分病例表现为高信号,可能与肿瘤出血有关,也可能与病理结构有关。PA病理组成有致密区和疏松区,当肿瘤以致密区组织为主时,导致水分子扩散受限,在DWI上可表现为以高信号为主的混杂信号。SWI中多数可见低信号,表明肿瘤内有存在微出血,与PA肿瘤的血管壁纤维组织发育不良有关。PWI表现均为低灌注,局部可有点片状高灌注,高灌注区域可能与肿瘤某些区域血管丰富有关。
MRS showed elevated Cho, decreased NAA and elevated Lac peaks. The elevated Lac peaks in PA were not necessarily caused by necrosis of tumors, because necrosis was rarely seen in PA, which might be related to changes in mitochondrial metabolism or changes in glucose utilization in low-grade tumors. The DWI signal of tumor tissue mainly depends on the ratio of nucleus to cytoplasm. The tight structure of tumor cells restricts the diffusion of water molecules, while the DWI signal increases and the ADC value decreases. The main manifestations of DWI are low signal intensity and high signal intensity in some cases, which may be related to tumor hemorrhage or pathological structure. PA pathology consists of dense and loose areas. When tumors are predominant in dense areas, the diffusion of water molecules is limited. On DWI, PA can show mixed signals with high signal intensity. Most of SWI showed low signal, which indicated that there was microbleeding in the tumors, which was related to the dysplasia of vascular wall fibrous tissue in PA tumors. PWI manifestations were hypoperfusion, local slices of hyperperfusion, hyperperfusion areas may be related to vascular enrichment in some areas of the tumor.
PA发生于小脑时主要需与血管母细胞瘤、髓母细胞瘤及室管膜瘤相鉴别
(1)血管母细胞瘤:好发于30-65岁成年人,多数呈大囊小结节样改变,瘤壁结节明显强化,内壁光整,形成“壁灯征”,并可见流空的血管,DWI表现为等或低信号。
Hemangioblastoma: Haemangioblastoma occurs predominantly in adults aged 30-65 years. Most of them show cystic nodule-like changes. The wall nodules are markedly enhanced and the inner wall is smooth, forming a 'wall lamp sign' and visible empty blood vessels. The DWI manifestations are iso-or hypo-signal.
(2)髓母细胞瘤：儿童后颅窝最常见的肿瘤,常与小脑蚓部关系密切,囊变少见,发生囊变时,囊变范围较小,囊壁光滑,一般无壁结节,壁常较厚。增强扫描以斑片状强化为主,其瘤内或边缘可见血管流空影,DWI多表现为明显扩散受限。
Medulloblastoma: The most common tumour in posterior cranial fossa of children is usually closely related to cerebellar vermis. Cystic degeneration is rare. When cystic degeneration occurs, the cystic degeneration range is small, the wall of the cyst is smooth, and there are usually no mural nodules, and the wall is often thicker. On contrast-enhanced scans, patchy enhancement was predominant. Vascular flow voids could be seen in the tumors or at the margins of the tumors, and DWI showed obvious diffusion limitation.
(3)室管膜瘤:多发生在第四脑室内,因此外周或一侧常包绕一薄层脑脊液,常造成梗阻性脑积水。多呈不规则形,常伴有钙化、囊变及出血,囊变一般为大囊。肿瘤不均匀强化,轮廓不光整,常伴有明显瘤周水肿。DWI表现为低信号或稍低信号.
Ependymoma: Ependymoma usually occurs in the fourth ventricle, so a thin layer of cerebrospinal fluid is often surrounded by the peripheral or side, often causing obstructive hydrocephalus. Most of them are irregular, often accompanied by calcification, cystic degeneration and hemorrhage. Cystic degeneration is usually a large cyst. The tumors were unevenly enhanced with irregular outlines and often accompanied by marked peritumoral edema. DWI showed low signal or slightly low signal.
PA发生于鞍区时主要需与颅咽管瘤、生殖细胞瘤及侵袭性垂体瘤相鉴别
(1)颅咽管瘤:瘤内常有出血及蛋壳状钙化,强化多不均匀,临床上常有垂体或下丘脑内分泌异常症状。
Craniopharyngeal angioma: Hemorrhage and eggshell calcification are common in the tumors, and the enhancement is uneven. Clinically, pituitary or hypothalamic endocrine abnormalities are common.
(2)生殖细胞瘤:缺乏典型的特点,可呈实性、囊实性,与鞍区毛细胞型星形细胞瘤较难鉴别,但生殖细胞瘤多较小,对放疗敏感,且常有下丘脑内分泌异常症状。
Germinoma: lack of typical characteristics, can be solid, cystic solid, and sellar hair cell astrocytoma is difficult to distinguish, but germinoma is mostly small, sensitive to radiotherapy, and often has abnormal symptoms of hypothalamic endocrine.
(3)侵袭性垂体瘤:中心常可见出血、坏死,常可见海绵窦受侵,颈内动脉被包绕征象,肿瘤内常有血管流空信号,垂体瘤常有内分泌异常症状。
Invasive pituitary adenoma: hemorrhage and necrosis are often seen in the center, invasion of cavernous sinus, encapsulation of internal carotid artery, void signal of blood vessels in the tumors, and endocrine abnormalities in pituitary adenomas.
PA位于大脑半球时主要需与多形性黄色瘤型星形细胞瘤、转移瘤相鉴别
(1)多形性黄色瘤型星形细胞瘤:好发于儿童和青少年,以大脑半球颞叶最常见,小脑及脊髓发病较罕见,肿瘤位置表浅。
Xanthomatous pleomorphic astrocytoma: It is predominant in children and adolescents. Temporal lobe of the cerebral hemisphere is the most common type, cerebellum and spinal cord are rare, and the location of the tumor is superficial.
(2)转移瘤:好发于老年人,呈不均匀环状强化,病灶周围水肿明显,病变可多发,多位于皮髓质交界处。
Metastases: Most of them occur in the elderly, with inhomogeneous ring enhancement, obvious edema around the lesion, and multiple lesions, mostly at the junction of cortex and medulla.
PS：预后：毛细胞星形细胞瘤是一种生长缓慢的肿瘤,患者可存活数十年,肿瘤全部切除后预后良好。
Prognosis: pilocytic astrocytoma is a slow-growing tumor. It can survive for decades. The prognosis is good after total removal of the tumor.
