Astrocytomas tend to have an infiltrative appearance, while ependymomas are localized and well marginated and when small may be centrally located in the spinal cord.

Astrocytomas tend to be long tumors, while ependymomas are shorter; astrocytomas may be holocord or even multifocal.

Cysts tend to be more common in astrocytomas than in ependymomas. Cysts occurring at the rostral and caudal ends of the tumors are called “polar cysts” (Fig. 27.2). The presence of these polar cysts does not favor a specific type of tumor.

Contrast enhancement is common in both and may not be used to different one from the other (Table 27.1). Rarely, astrocytomas may show no contrast enhancement.

Older and newer blood products (including diffuse superficial siderosis) are more much common in ependymomas than in astrocytomas (Fig. 27.3).

Calcifications are uncommon in both tumors and generally not appreciated as tumors get mostly studied with MRI and not computed tomography.

Glioblastomas have no specific imaging features but are characterized by very rapid growth despite aggressive therapies [3] (Fig. 27.4).

Despite the fact that spinal cord ependymomas are more common in patients with NF-2, they still tend to be relatively rare even in that setting. Like all ependymomas, they arise from the ependymal cells – in this case those lining the central canal of the spinal cord (Fig. 27.5). They tend to have a slow and indolent clinical course and remain histologically of low grade, and their treatment is controversial and not well established. Ependymomas arising in NF-2 patients tend to be more common in males and involve predominantly the cervical cord and lower brainstem.

Although there are inherent technical difficulties in obtaining diffusion tensor imaging (DTI) tractography (AKA: fiber tracking) studies in the spinal cord, recently several publications have emphasized its usefulness [5–9]. Since the major predictor of prognosis and survival is tumor respectability, DTI may provide information not available by other diagnostic preoperative means. One of the most important information neuroimaging provides to the surgeon is if a tumor is localized and thus resectable or infiltrative and thus unresectable. Based on this information the neurosurgeon can plan for a multilevel laminectomy or a single one for the sole purpose of biopsy. In one study, 14 patients with spinal cord tumors underwent DTI using a 3.0 T unit [6]. Fiber course was evaluated and based on it tumors were classified as resectable or non-resectable and then compared with the intraoperative findings. If the lesions did not contain any fibers or if only a few fibers were visible within them, they were considered as resectable and at surgery all of them were ependymomas (Fig. 27.6). Lesions containing a multitude of fibers and considered non-resectable were proven to be astrocytomas, lymphomas, or multiple sclerosis (Figs. 27.7 and 27.8). These findings are similar to those of a smaller study in which DTI showed intra-tumoral fibers in five astrocytomas [9]. Interestingly, in this last study DTI was unable to differentiate peri-tumoral edema from true tumor infiltration (similar findings have been noted in the evaluation of brain tumors). In the study previously mentioned that included 14 patients with a variety of spinal cord lesions evaluated with DTI, the findings in one patient with a pilocytic astrocytoma also showed displacement of fibers only [6]. Thus, it seems that DTI holds promised in preoperatively separating resectable from non-resectable spinal cord tumors. It is also to be remembered that localizing tumor-associated cysts is also very important for the neurosurgeon. Any large cyst may need to be decompressed to ameliorate symptoms regardless if the tumor will be completely resected or only biopsied.

Because the traditional imaging features of most spinal cord tumors may overlap, it is important to be familiar with their differential diagnosis. Gangliogliomas are rare primary tumors that are much more common in children than in adults and account for only 1 % of all spinal cord masses [10]. These tumors are slow growing, a fact reflected by the long-standing symptoms (about 5 years in average) reported by the patients. Most spinal cord gangliogliomas are WHO grade II, but some are grade III (anaplastic) and their localized variant (grade I) corresponds to the gangliocytoma [1]. Other variants such as ganglioglioneurocytomas and glioneurofibroma are very rare and generally present before 3 years of age. There are no specific imaging features but most gangliogliomas are extensive (more than eight vertebral bodies in length) and tend to arise in the cervical region; thus, they are the most important alternative diagnosis to astrocytoma. Enhancement is perhaps less common and less intense than that seen in astrocytomas; calcifications may occur, but overall the diagnosis remains a histological one and they cannot be differentiated from astrocytomas by imaging alone.

Oligodendrogliomas arising in the spinal cord are very rare [1]. They tend to be found in younger patients and most of them are WHO grades II and III. Their imaging characteristics are nonspecific. These tumors are infiltrative in nature. Subependymomas are variants of ependymomas which more often arise in the cervical spinal cord [1]. Their imaging features are also nonspecific.

Other rare neoplasias to be included in the differential diagnosis include spinal cord lymphoma, sarcomas (which can be de novo or arise years after radiation therapy), and melanocytomas and melanomas (which may be of high signal intensity on pre-contrast T1-weighted images, a finding that suggests their nature) (Table 27.2) (Fig. 27.9).