Spinal cord astrocytomas: Rare but life-threatening tumors in children

IMSCTs occur most often in children between the ages of 1 and 5 years, with an equal prevalence in males and females.3,4 Although the overall incidence of spinal cord astrocytomas is low (0.8-2.5 per 100,000 population per year),7 these tumors are the most common IMSCT in the pediatric population.4 Spinal cord astrocytomas are usually located in the cervical or thoracic spine, with 75% found in these regions. Only 20% are found in the distal spinal cord, while a rare 5% are found in the filum terminale.4

Although no specific risk factors for astrocytomas have been clearly identified,8 associations have been made with such inherited conditions as Li-Fraumeni syndrome, Turcot syndrome, tuberous sclerosis, and neurofibromatosis. In rare cases, previous radiation for other neoplasms has been associated with the development of astrocytoma of the spinal cord.4

CLINICAL PRESENTATION

Astrocytomas are initially asymptomatic. Development of symptoms depends on the grade of the tumor, with highgrade lesions causing more rapid symptom progression.7 Localized, midline back pain is the presenting symptom in 70% of children with intramedullary spinal cord astrocytomas.1 Patients frequently complain of dull, shooting pain that wakes them from sleep.2,9 The exact mechanism by which astrocytomas of the spinal cord cause pain is unknown;7 possible explanations include direct pressure on the dura by the enlarging spinal cord, nerve-root impingement, or abnormal muscle innervation.7 Nocturnal pain is thought to be due to increased pressure on the spinal cord from venous congestion that occurs when lying down.5,9 Other sensory complaints include paresthesias and changes in perception of pain and temperature.4,7 Dysesthesias—uncomfortable sensations of numbness and tingling or hot and cold—are also described.5

As the tumor grows and impinges on motor neurons, the child may experience motor dysfunction manifested by weakness, clumsiness, gait disturbance, and frequent falls.2,4,5,7 Younger children may exhibit regression of motor function, such as reverting to crawling after having learned to walk.5 Altered sphincter tone leading to changes in bowel or bladder function is a sign of advanced disease.1,4,5,7

Physical examination of the child reveals abnormal neurologic findings, including hyperreflexia, spasticity, decreased sensation, and decreased proprioception.4,5,7 Muscle atrophy may be noted as a consequence of prolonged weakness.3 One-third of children with astrocytoma of the spinal cord will present with a spinal cord deformity, such as scoliosis or torticollis.2,5 Scoliosis is the most common presenting sign in patients with thoracic lesions.1 Rarely, patients will present with hydrocephalus due to tumor cells in the subarachnoid space.5,7

DIAGNOSIS

MRI with or without contrast is the imaging study of choice for spinal cord tumors.2 Astrocytomas appear heterogeneous and asymmetric with poorly defined borders on MRI4 and enhance with gadolinium contrast on T1-weighted imaging.7 Also visible on MRI are surrounding spinal cord edema, scoliosis, hemorrhage, and areas of infarction.2,7 Cysts associated with the tumor, which are present in 40% of cases, do not enhance with contrast2 but are visible on T2-weighted imaging.5 If MRI is contraindicated because of previous surgery with metal implants, CT myelography is the diagnostic test of choice.5

Because spinal cord malignancy is rare and the differential diagnosis of back pain in children is broad, the workup often begins with plain radiographs.3 Nonspecific findings, such as spinal canal enlargement or scoliosis, may be noted on the plain radiographs from the initial evaluation.7 If a lumbar puncture is performed, CSF analysis may show increased protein levels. This is also a nonspecific abnormality; lumbar puncture is not useful in the diagnosis of CNS tumors.7

The final diagnostic evaluation of spinal cord astrocytomas is based on histologic tumor grading. The grading of astrocytomas is based on the World Health Organization (WHO) scale. Low-grade astrocytomas include WHO grade I (pilocytic) and grade II (diffuse) tumors. Pilocytic astrocytomas are the most common grade diagnosed in children.4 WHO grade III (anaplastic) and IV tumors (glioblastoma multiforme) are considered high-grade and show increased cellularity, anaplasia, and vascular proliferation.4,8,10 In the pediatric population, highgrade tumors make up only 7% to 25% of astrocytomas.7

Differential diagnosis The differential diagnosis of astrocytomas includes other types of spinal cord tumors as well as benign conditions that cause back pain (see Table 1), which as previously noted is a common presenting symptom  of astrocytomas in children. Back pain can be due to trauma or musculoskeletal strain (for example, from carrying a heavy backpack).11 Trauma to the back can lead to disk herniation, vertebral fractures, or epidural hematomas. Less common causes of back pain include osteomyelitis, diskitis, epidural abscess, urinary tract infection, or sickle cell crisis. Chronic back pain can be caused by inflammatory disorders, such as juvenile rheumatoid arthritis or ankylosing spondylitis.11 Careful history-taking from the child or parents is needed to determine if trauma has occurred or if the child is at risk for other causes of back pain. A history of acute or subacute onset of back pain with nighttime symptoms in the absence of trauma or a history of back pain that is prolonged or unremitting with conservative treatment raises suspicion for a neoplastic etiology.

Spinal cord tumors that differ histologically from astrocytomas include gangliomas, ependymomas, meningiomas, primitive neuroectodermal tumors, and nerve-sheath tumors.3 Although diagnosed by biopsy or excision, these lesions also have MRI characteristics that distinguish them from astrocytomas. Extramedullary malignancies that cause back pain include osteoid osteoma, osteoblastoma, Ewing's sarcoma, leukemia, and lymphoma.11,12