Imaging Analysis of Primary Malignant Intracranial Lymphoma

Discussion

PCNSL is usually seen in patients above 60 years old and mostly in males^[5,6]. In this study, most patients were male and over 50 years old which showed in accordance with the reports in the literature. PCNSL is mostly non-Hodgkin lymphoma (NHL). The resutls of the histological examination shown in the literature demonstrated that most of them were B-cell lymphoma while few were T-cell lymphoma^[7,8]. All cases in this study were B-cell lymphoma, in which most were diffuse large B-cell lymphoma. Eight out of the 9 cases were diffuse large B-cell lymphoma and another case was diagnosed as low grade B-cell lymphoma originated from primary dural lymphoma, which arises from the dura mater that envelops the CNS, therefore, the brain parenchyma wasn’t directly involved. There were reports that 55% of PCNSL occurred at supratentorial corpus callosum and cerebral white matter around the ventricles and 17% occurred at basal ganglia, thalamus, and subthalamus region, while 11% were located at posterior cranial fossa. Less than 1% was located at spinal cord. Most cases with PCNSL had single lesion while 20%-44% of the cases had multiple lesions^[9-11]. The results of the study were similar to those reported in the literature, that is, the tumor localized in supratentorial region, deep cerebral white matter, ventricles, and around corpus callosum in 8 patients. Some reported that most cranial lymphomas could infiltrate ependyma and pia mater and spread along them^[12-14]. There was only 1 case in this study that could be observed the spread of tumor to ependyma. The reason for such low incidence rate of this spread in ependyma is still unknown. The subdural lesions infiltrated pia mater. Enhanced scan would reveal “dural tail sign”. This case confirmed by the surgical and pathological examinations, was proved to be low grade B-cell lymphoma, originating from primary lymphoma at dural marginal zone. Different from the tumor originated from deep brain parenchyma, some scholars even identified intracranial lymphoma of primary dural marginal zone lymphoma as a special type. It has low malignancy and does not spread along ependyma, while it is sensitive to simple, low-dosage chemotherapy^[15]. PCNSL of dural origin is located at a very rare place compared with the locations of other cranial lymphomas and it, pathologically, belongs to mucosa associated lymphoid tissue (MALT). Although there is no MALT tissue in the central nervous system, it has been hypothesized that meningthelial cells are embryologically analogous to epithelial cells at other sites where MALT lymphoma arises. In view of this, it has, therefore, been proposed that these dural lymphomas are likely to arise where meningothelial cells are mostly numerous. Although these cells occur throughout the arachnoid membrane, they are concentrated in the arachnoid villi within the dural venous sinuses^[16,17]. Because of similarity in MRI, dural lymphoma is difficult to distinguish from meningioma by imaging before surgery. In this study, this case with dural marginal zone lymphoma was misdiagnosed as meningioma before surgery. Primary distinctions by enhanced MRI were that the enhanced imaging of dural lymphoma didn’t show as obviously as convex surface of the meningioma did. The pathological types of PCNSL are supposed to get excellent outcomes from receiving chemotherapy and radiotherapy after surgery. The patient in this study received periodic chemotherapy and showed no recurrence when re-examined by imaging detection 2 years after surgery

Although preoperative diagnosis of PCNSL is difficult, CT and MRI are still helpful in recognizing the characteristic changes for PCNSL. Learned from the experience of the 9 cases and from the reports in literature, the features of the PCNSL are concluded in the followings. The lesion is often single and distributed at supratentorial region mostly including subcortical white matter, ventricles, and corpus callosum. The lesions show slightly lower signals in T1WI, equal or high signals in T2WI. The signals are more homogenous in strength. The cystic lesion, necrosis, hemorrhage, calcification are rarely seen. The edemata around the lesions are light and the occupational effects ranging from light to medium degree are demonstrated in the images. Intracranial lymphoma grows by way of infiltration from one or some lymphoma cells to the peripheral tissues of Virchow-Robin space, destroying blood brain barrier. After enhanced scan, the lesions shown on the images are dramatically strengthened and sometimes, they are enhanced in “block-like” or “fist-like” fashion. Primary intracranial lymphoma has another characteristic of being inconsistent in the volume of tumor with surrounding edema. Most tumors have relatively larger volume, while less edema in the surrounding tissues of the tumor. This phenomenon is more prominent at mid-line and deep part near ventricles^[8,12,13].

Few cases have no typical imaging manifestations, which are similar to the presentations shown by MRI for some other intracranial occupying lesions. This disease needs to be differentiated from other cranial tumors or tumor-like lesions listed below. i) Carcinomatosis, patient usually can provide history of primary tumor of the other organs, except of brain. Most intracranial carcinomatoses are located at joint location of gray and white matters. T1WI shows low signal and T2WI shows high signal, with significant edema around tumor and occupational effect. The circular or irregular enhancement of lesions is shown in enhanced scan due to necrosis in the center of the lesion. ii) Glioblastoma multiforme, this type of tumor usually shows larger and irregular lesion of necrotic cystic with unclear boundary. The lesion is lobed and heterogeneous in texture, while occupational effect is more severe and edema surrounding the tumor is more severe as well. The lesion of lymphoma’s cystic is rarely seen and the edema is lighter with lightly occupational effect. It can easily invade ependyma. iii) Meningioma, it is usually located on the surface of the brain or meninges near the skull base. The meninges is attached to the wide based part in the intracranial side. Differential points are “sign of relocated white matter” and “meningeal tail sign”. Cortex is compressed, causing “white matter compression sign” and enhanced scan shows “meningeal tail sign”. The enhanced scan on lymphoma located in the dura mater is not as obvious as that on convex surface of meningioma. But, the priority is that the differential diagnosis of intracranial lymphoma of dural marginal zone and meningioma is extremely difficult.

Overall, clinical and MRI manifestations of primary intracranial lymphoma are as follows. i) It usually occurs in patients at the age of 60 years old and the lesion could be single or multiple. The lesions are usually located at deep white matter of subcortex, ventricles, and around corpus callosum. ii) The lesions are in round or irregular shape with clear boundaries. T1WI shows low signal and T2WI shows equal or high signal. The signals are homogenous. iii) The edema around the tumor or its occupational effect is slight. There is an inconsistency regarding the volume of tumor and regarding the edema around the tumor between the images and the true specimens taken from the surgery. iv) Enhanced scan shows the lesions in well-balanced enhancement. They are enhanced in “block-like” or “fist-like” fashion. v) It can invade ependyma and pia mater, while further spread around along these parts. vi) It is sensitive to radiotherapy and chemotherapy.