核磁共振成像：脑白质损伤？还是肿瘤复发？

根据一项最新研究发现：用于治疗两种类型大脑肿瘤（小脑幕上原始神经外胚瘤与成神经管细胞瘤）的大剂量化疗与放疗，能够导致大脑白质在核磁共振成像检查（magnetic resonance imaging，MRI）的时候上产生肿瘤样的改变。

该研究由来自St. Jude儿科研究医院（ St. Jude Children’s Research Hospital，Memphis，TN，USA）研究人员完成。该研究报道说：这种损伤被称为大脑白质损伤（white matter lesions，WMLs），会被误认为肿瘤复发，从而促使医生采用更加激进的方式（实际上是不必要的）治疗患者，即使用更大剂量的化疗和放疗。

St. Jude医院神经肿瘤科主任，该研究项目的主要作者Amar Gajjar医学博士在文章中写道：“放疗与大剂量化疗是一种我们希望尽可能保守地使用的治疗方法。这个新发现给广大临床医生提供了一个极其重要的警告，否则他们会将大脑白质损伤误认是实际存在需要进一步治疗的肿瘤。”该文章发表在2004年11月15日的《临床肿瘤学期刊》上（the Journal of Clinical Oncology）。

脑白质损伤经常发生于手术后接受放疗和大剂量化疗的成神经管细胞瘤或者小脑幕上原始神经外胚瘤患者。这项研究也是第一次在儿童脑肿瘤患者中评估大脑白质的这种变化对智力的影响。特别是这项研究发现：出现脑白质损伤与神经认知、或者智力、功能的下降有关。

这篇文章的主要作者之一，St. Jude医院血液科-肿瘤科的Maryam Fouladi医学博士说：“对绝大多数儿童患者而言，接受治疗后进行核磁共振扫描所发现的病变是脑白质损伤而不是癌症。医生可以反复使用核磁共振扫描来随访这些最初的病变，以确定脑白质损伤是否消失。如果确实消失了，那就不是癌症也就无需治疗。但是即使这些病变是暂时的，有些出现这种病变的儿童却发展成永久的神经系统病变，例如吞咽困难。”

该项研究涉及了127例脑癌患者，在接受治疗后随访了13个月。在这期间，患者中有22例由于治疗而出现了脑白质损伤。在检测到损伤后23.5个月内有16例患者（73％）脑白质损伤消失。有2例患者脑白质损伤分别持续了19个月和31个月。其它2例患者尽管仍然存在脑白质损伤，但是仍然再次形成了肿瘤。其余患者的脑白质损伤导致了组织破坏，出现脑白质损伤的患者的智商测验和数字计算能力显著降低。

研究者总结说：小脑幕上原始神经外胚瘤与成神经管细胞瘤的患者接受放疗和大剂量化疗后，脑白质损伤通常短期存在，并不产生症状。但是，脑白质损伤能够与肿瘤复发的早期阶段发生混淆，从而使得医生很难准确判断肿瘤是否复发。

MRI May Show Brain Lesions as Tumors
 
High-dose chemotherapy and irradiation used to tread two types of brain tumors--supratentorial primitive neuroectodermal tumor (PNET) and medulloblastoma--can cause alterations in the brain’s white matter that appear like tumors when seen on magnetic resonance imaging (MRI) scans, according to a new study.

The study, conducted by researchers from St. Jude Children’s Research Hospital (Memphis, TN,USA; www.stjude.org), report that this damage, called white matter lesions (WMLs), can be mistaken for recurrent tumors, prompting physicians to treat the patient aggressively--and unnecessarily--with more chemotherapy and radiation.

“Irradiation and high-dose chemotherapy are treatments we want to use as sparingly as possible. This new information represents an important caution sign for physicians who otherwise might assume that WMLs are actually tumors that need further treatment,?said Amar Gajjar, M.D., director of neuro-oncology at St. Jude and senior author of the study, published in the November 15, 2004, issue of the Journal of Clinical Oncology.

WMLs often occur in patients with medulloblastoma or PNET who have been treated with radiation and high-dose chemotherapy following surgery. This research is also the first to observe the effect of these changes in white matter on intellectual outcome in children with brain tumors. Particularly, the study discovered the presence of WMLs is linked with a decline in neurocognitive, or intellectual, function.

“In the vast majority of children, the changes seen on MRI scans after treatment are WMLs and not cancer. Physicians can follow up these initial findings with repeat MRI scans to determine whether the WMLs disappear. If they do disappear, then it wasn’t cancer and didn’t require treatment. But even though these changes tend to be only temporary, some children with these changes tends to develop permanent neurologic problems, such as difficulty swallowing,?said Maryam Fouladi, M.D., from the department of hematology-oncology at St. Jude and lead author of the report.

The study was comprised of 127 patients who were followed for up to 13 months after the initial treatment for brain cancer. During the time, 22 of these patients developed WMLs following the treatment. The WMLs disappeared in 16 patients (73%) within 23.5 months after being detected. In two patients the WMLs remained after 19 and 31 months, respectively. Two other patients developed tumors again while still showing evidence of WMLs. In the remaining patients, the WMLs led to tissue breakdown, and patients with WMLs experienced a significant decrease in estimated IQ and math scores.

The investigators concluded that in patients with medulloblastomas or PNET who had been treated with irradiation and high-dose radiation, WMLs are typically short-lived and do not cause symptoms. WMLs, however, can mimic the early stages of tumor recurrence, and therefore make it hard for physicians to effectively diagnose tumor recurrence.