根據(jù)一項(xiàng)最新研究發(fā)現(xiàn)：用于治療兩種類型大腦腫瘤（小腦幕上原始神經(jīng)外胚瘤與成神經(jīng)管細(xì)胞瘤）的大劑量化療與放療，能夠?qū)е麓竽X白質(zhì)在核磁共振成像檢查（magnetic resonance imaging，MRI）的時(shí)候上產(chǎn)生腫瘤樣的改變。

該研究由來自St. Jude兒科研究醫(yī)院（ St. Jude Children’s Research Hospital，Memphis，TN，USA）研究人員完成。該研究報(bào)道說：這種損傷被稱為大腦白質(zhì)損傷（white matter lesions，WMLs），會被誤認(rèn)為腫瘤復(fù)發(fā)，從而促使醫(yī)生采用更加激進(jìn)的方式（實(shí)際上是不必要的）治療患者，即使用更大劑量的化療和放療。

St. Jude醫(yī)院神經(jīng)腫瘤科主任，該研究項(xiàng)目的主要作者Amar Gajjar醫(yī)學(xué)博士在文章中寫道：“放療與大劑量化療是一種我們希望盡可能保守地使用的治療方法。這個(gè)新發(fā)現(xiàn)給廣大臨床醫(yī)生提供了一個(gè)極其重要的警告，否則他們會將大腦白質(zhì)損傷誤認(rèn)是實(shí)際存在需要進(jìn)一步治療的腫瘤。”該文章發(fā)表在2004年11月15日的《臨床腫瘤學(xué)期刊》上（the Journal of Clinical Oncology）。

腦白質(zhì)損傷經(jīng)常發(fā)生于手術(shù)后接受放療和大劑量化療的成神經(jīng)管細(xì)胞瘤或者小腦幕上原始神經(jīng)外胚瘤患者。這項(xiàng)研究也是第一次在兒童腦腫瘤患者中評估大腦白質(zhì)的這種變化對智力的影響。特別是這項(xiàng)研究發(fā)現(xiàn)：出現(xiàn)腦白質(zhì)損傷與神經(jīng)認(rèn)知、或者智力、功能的下降有關(guān)。

這篇文章的主要作者之一，St. Jude醫(yī)院血液科-腫瘤科的Maryam Fouladi醫(yī)學(xué)博士說：“對絕大多數(shù)兒童患者而言，接受治療后進(jìn)行核磁共振掃描所發(fā)現(xiàn)的病變是腦白質(zhì)損傷而不是癌癥。醫(yī)生可以反復(fù)使用核磁共振掃描來隨訪這些最初的病變，以確定腦白質(zhì)損傷是否消失。如果確實(shí)消失了，那就不是癌癥也就無需治療。但是即使這些病變是暫時(shí)的，有些出現(xiàn)這種病變的兒童卻發(fā)展成永久的神經(jīng)系統(tǒng)病變，例如吞咽困難。”

該項(xiàng)研究涉及了127例腦癌患者，在接受治療后隨訪了13個(gè)月。在這期間，患者中有22例由于治療而出現(xiàn)了腦白質(zhì)損傷。在檢測到損傷后23.5個(gè)月內(nèi)有16例患者（73％）腦白質(zhì)損傷消失。有2例患者腦白質(zhì)損傷分別持續(xù)了19個(gè)月和31個(gè)月。其它2例患者盡管仍然存在腦白質(zhì)損傷，但是仍然再次形成了腫瘤。其余患者的腦白質(zhì)損傷導(dǎo)致了組織破壞，出現(xiàn)腦白質(zhì)損傷的患者的智商測驗(yàn)和數(shù)字計(jì)算能力顯著降低。

研究者總結(jié)說：小腦幕上原始神經(jīng)外胚瘤與成神經(jīng)管細(xì)胞瘤的患者接受放療和大劑量化療后，腦白質(zhì)損傷通常短期存在，并不產(chǎn)生癥狀。但是，腦白質(zhì)損傷能夠與腫瘤復(fù)發(fā)的早期階段發(fā)生混淆，從而使得醫(yī)生很難準(zhǔn)確判斷腫瘤是否復(fù)發(fā)。

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.