Focal spinal cord lesions, which can either be neoplastic or non-neoplastic, are rare in children. The literature has extensively described spinal cord neoplasms as a separate entity. Both neoplastic and non-neoplastic lesions, however, may present with similar clinical findings; hence, differentiating among them with imaging remains crucial to their management. Our objective is to focus on imaging features that help distinguish neoplastic lesions from non-neoplastic lesions. Magnetic resonance imaging (MRI) is the most sensitive imaging modality in the diagnosis and follow-up of these lesions.
Background and approach
Spinal cord tumors account for only 0.5% to 1% of all central nervous system (CNS) neoplasms. They are especially rare in childhood, with a frequency of 0.19 per 100,000 person-years, according to the Central Brain Tumor Registry of the United States. A third of all intraspinal tumors are located intradurally and intramedullary; in children, most intramedullary tumors are malignant and are most commonly glial tumors. The patient’s age at presentation varies without sex predilection.
Clinically, spinal cord lesions often present nonspecifically; symptomology can vary from a sudden onset to a slowly progressive course. Misleading and vague symptoms can often result in delayed diagnosis and, thus, increased morbidity. Progressive scoliosis, gait disturbance, motor weakness and, most importantly, back pain should raise the possibility of a spinal cord tumor and prompt imaging assessment. In children with back pain, MRI of the entire spine should be performed, since pain can be referred from a higher or lower level than the actual lesion location. The vast majority of spinal cord tumors are treated with debulking surgery. Follow-up imaging for residual disease and recurrence is often necessary, further favoring MRI over CT as the imaging modality of choice. Functional sequences, such as diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI), provide detailed anatomical location of the tumor and its relationship to important neural tracts.1
Spinal cord neoplasms
Most spinal cord neoplasms are glial tumors: astrocytomas (60%) and ependymomas (30%). Nonglial tumors include ganglioglioma/gangliocytomas, teratomas, hemangioblastomas, metastases, primitive neuroectodemermal tumor (PNETs), germ cell tumors, and melanomas; these constitute about 10% of all spinal cord tumors (Table 1). Focal cord expansion is the most typical MR imaging feature of spinal cord tumors. Other salient imaging characteristics include variable contrast enhancement and cyst formation. If there is no focal cord expansion or considerable mass effect, non-neoplastic etiologies should be considered first. Cysts can be tumoral or nontumoral. Non-tumoral cysts are usually present in the cranial and caudal poles of a tumor and typically do not enhance. Tumoral cysts, on the contrary, typically present within the tumor and demonstrate peripheral contrast enhancement.
Glial tumors of the spinal cord
Astrocytomas, which are more commonly seen in children than in adults, are also the most common spinal cord neoplasms in children. They arise most often in the cervico-thoracic region, and they generally present with pain and motor dysfunction, followed by gait disturbance and scoliosis. Most astrocytomas are WHO grades I and II (75%) that include pilocytic and fibrillary types. Astrocytomas are infiltrative and eccentric in location, resulting in asymmetric cord expansion. Cysts, both polar and intratumoral, are a common feature, occurring 20% to 40% of pediatric cases.
Astrocytomas are typically T2-hyperintense, T1-iso- or hypointense, and they may show patchy, mild-moderate contrast enhancement.2 Enhancement is less sharply demarcated from the nonenhancing tissue and their tumoral margins usually extend beyond the enhancing tissue. Unlike ependymomas, hemorrhage, or calcification is rare with atrocytomas. Peritumoral edema presents with increased T2 signal in the tumor periphery, a feature common to all glial tumors. Astrocytomas affecting the entire cord from the cervicomedullary junction to the conus have been reported in children, leading to the term “holocord astrocytoma.”3 Cyst formation extending over several vertebral segments is common, with associated enhancement of the interspersed solid components (Figure 1).
Although they are the most common intramedullary glial tumor in adults, ependymomas are the second most common spinal cord neoplasms in children. They occur most often in the cervical region with 44% involving the cervical cord alone and 23% extending into the upper thoracic region. These tumors arise from the ependymal cells of the central canal; hence, they are located centrally, as opposed to the eccentric location of astrocytomas (Table 2). Given the central location, in proximity to spinothalamic tracts, sensory symptoms are frequently observed. Almost all spinal cord ependymomas can be classified as either WHO grade I or WHO grade II.4 Rather than being infiltrative, the tumors are well defined and tend to compress adjacent neural tissue.
Most ependymomas are T1-iso- or hypointense relative to the spinal cord.4-6 They are typically T2 hyperintense relative to the spinal cord,5,6 although in the single largest review of spinal ependymomas, isointense tumors were equally common.5 Tumor margins are usually sharp, and T2-signal alterations correspond well with the enhancing solid tumor. Ependymomas demonstrate stronger and more homogenous enhancement than do astrocytomas. Hemorrhage is common, and the “cap sign,” representing a rim of hemosiderin resulting from intratumoral hemorrhage, can be seen in the cranial or caudal margin of the tumor.
Myxopapillary ependymoma is a benign ependymoma, composing 40% to 50% of all ependymomas in adults, but more rarely seen in children. Myxopapillary ependymomas constitute about 13% of all spinal ependymomas in children and are more common in males. These tumors typically arise from the ependymal glia of the conus medullaris and filum terminale. On the basis of their location, they present with lower back, leg, or sacral pain, and muscle weakness or sphincter dysfunction. They typically fill the intradural space, have a lobulated contour, and may result in scalloping of the posterior vertebral bodies. Myxopapillary ependymomas are typically T1-isointense and T2-hyperintense relative to the spinal cord (Figure 2). Internal punctate foci of T1- and T2-hyperintense signal may be noted, reflecting either mucin content or hemorrhage.6 Avid enhancement with contrast is seen.
Nonglial spinal cord tumors
Ganglioglioma/gangliocytomas are low-grade (WHO grade I) tumors composed of well-differentiated ganglion/neuronal cells, with (ganglioglioma) or without (gangliocytoma) a glial component. They are most common in children and young adults with a mean age of 12 years at presentation.7 The tumor typically originates from the sympathetic chain ganglia and is the most benign form of neurogenic tumor. T1 signal can be mixed, possibly secondary to a dual cell population (Figure 3). T2-weighted images are generally hyperintense. Surrounding edema is not as frequently seen as with ependymomas or astrocytomas.7,8 Patchy enhancement with contrast is seen, as reported by Patel et al, in 65% of cases.7 Tumoral cysts are more common in gangliogliomas than in astrocytomas or ependymomas.8
Spinal cord teratomas are extremely rare neoplasms. Teratomas of the CNS comprise tissues derived from all 3 germ cell layers; they are categorized as mature, immature, and malignant Poeze et al observed a wide age range of patients at presentation; however, in children they are most often seen in the second decade.9 Demonstrating a predilection for the lumbosacral spine, the lesions most frequently have mixed solid and cystic components with fat and calcifications (Figure 4). T1- and T2-hyperintense signal foci are typically seen and suggestive of fat or calcification. The contrast enhancement pattern varies, and most teratomas are diagnosed on histopathological examination.
Intramedullary spinal metastases are rare, representing only about 2% of all metastases to the CNS.8 Intramedullary metastases may result from hematogenous spread or from direct extension from the leptomeninges. Intradural extramedullary metastases are far more common than intramedullary metastases in children. Seeding typically arises from intracranial neoplasms, such as medulloblastomas, ependymomas, anaplastic astrocytomas, or germinomas. The lumbosacral spine is typically involved with gravitation of tumor cells and seeding. Nodular tumoral deposits can be seen anywhere along the leptomeninges. Thickening of the thecal sac and nerve roots with intense homogenous contrast enhancement is typical. (Figure 5).
Demyelinating, autoimmune, inflammatory or vascular lesions of the spinal cord may present with neurological symptoms and signs similar to those of tumors. Non-neoplastic lesions are generally treated medically. MRI remains the mainstay for differentiating between neoplastic and non-neoplastic lesions. Non-neoplastic focal spinal cord lesions typically present with much less cord expansion than do neoplasms. Multifocal involvement strongly favors non-neoplastic lesions, such as demyelinating diseases.1 Some examples are discussed below.
Acute disseminated encephalomyelitis (ADEM)
ADEM is commonly seen late in the course of a viral disease or after vaccination, and less commonly after a bacterial infection or drug ingestion. The most common clinical presentation is a focal neurological deficit that evolves and tends to resolve over a period of weeks. Most patients make a complete recovery; however, rarely permanent neurological sequelae can be seen. Recurrent or multiphasic presentations can be seen. Cases initially diagnosed as ADEM may eventually be diagnosed as multiple sclerosis.10 White matter tracts in the brainstem and spinal cord are involved in approximately 50% of all patients. Areas of demyelination present with T1 and T2 prolongation on MRI. Various patterns of enhancement can be seen in the subacute phase. Every case with suspected demyelinating disease involving the spinal cord should be complemented with brain MRI. Multifocal presentation is far more common than unifocal presentation. Brain imaging reveals involvement of white matter in the subcortical and periventricular locations both in the supratentorial and infratentorial brain. Up to 50% of cases demonstrate demyelination in basal ganglia as well.
Multiple sclerosis (MS)
Multiple sclerosis is a demyelinating disease of the CNS, which typically takes a relapsing-remitting course. MS typically presents between 20 and 40 years of age and is more common in women. Children under age 16 years make up about 5% of all cases. An MS diagnosis requires multiple episodes of focal neurologic deficits separated in time and space.10 Typically, multiple foci of demyelinating plaques are seen in white matter of the spinal cord, with surrounding mild edema. Contrast enhancement may suggest active demyelination. Brain involvement is seen in most cases, with bilateral asymmetrical involvement of the periventricular and subcortical white matter. Demyelinating plaques in the periventricular white matter and corpus callosum are more commonly seen in MS than in ADEM.
Idiopathic acute transverse myelitis
Idiopathic acute transverse myelitis (IATM) is an autoimmune myelitis that results in bilateral motor, sensory, and autonomic dysfunction. MRI findings are nonspecific and remain a diagnosis of exclusion. MR imaging findings reveal smooth cord expansion with T1-iso or hypointense signal, T2-hyperintense signal and variable enhancement with contrast. The top differential diagnosis of IATM is ADEM, multiple sclerosis (MS), neuromyelitis optica (NMO), spinal cord infarct, and neoplasm.
Spinal cord neoplasms can obstruct cereprospinal fluid flow and mimic syringohydromyelia. Hydromyelia is characterized by dilatation of the central canal of the spinal cord (transverse diameter of the canal exceeds 2 mm). Syringomyelia refers to an eccentric CSF-filled cavity that may reflect a prior insult to the cord parenchyma. Patients with first-time diagnosis of syringohydromyelia should have their MR imaging completed with contrast to rule out the possibility of tumor.
Focal spinal cord lesions in children are rare, with 90% of lesions representing glial tumors, astrocytomas, and ependymomas. Back pain is a serious presentation in children and should be appropriately worked up. The location, degree of cord expansion, enhancement pattern, and solitary versus multiplicity of lesions help to differentiate neoplastic from non-neoplastic lesions.