Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (103 page)

Cytologic evaluation of the CSF may provide sufficient diagnostic material to avoid brain biopsy in some patients. The meninges are involved in <30% of patients with malignant lymphoma. Involvement is most prevalent in diffuse large cell (“histiocytic”), lymphoblastic, and immunoblastic lymphoma and occurs in 30–50% of patients with Burkitt lymphoma and 15–20% of patients with nonHodgkin lymphoma.
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Hodgkin disease seldom involves the CNS.

Evaluation of the CSF often reveals an elevated protein and a lymphocytepredominant pleocytosis. The glucose level is usually normal but may be decreased if there is leptomeningeal disease. Abnormal cells found in the CSF may be differentiated by immunohistochemistry, immunofluorescence, or flow cytometry. PCR may also be used for identification of clonality. The demonstration of neoplastic lymphocytes in the CSF on cytologic evaluation or flow cytometry is sufficient for the diagnosis of CNS lymphoma.
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References

1.  Fischer L, Martus P, Weller M, et al. Meningeal dissemination in primary CNS lymphoma: prospective evaluation of 282 patients.
Neurology.
2008;71:1102.

2.  Abrey LE, Batchelor TT, Ferreri AJ, et al. Report of an international workshop to standardize baseline evaluation and response criteria for primary CNS lymphoma.
J Clin Oncol.
2005;23:5034.

SPINAL CORD TUMOR

   Definition

Spinal cord tumors occur within the cord parenchyma or membranes adjacent to the cord. They may be primary or metastatic. Primary spinal cord tumors account for 2–4% of all primary CNS tumors. Extradural tumors are usually metastatic and can cause spinal cord compression.
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Tumors arising within the dura, outside of the spinal cord, are termed intradural–extramedullary and comprise the nerve sheath tumors and meningiomas. Tumors arising within the spinal cord itself are called intramedullary tumors, predominantly gliomas (astrocytomas or ependymomas).
^2,3

   Clinical Presentation

Patients present with progressive symptoms that vary based on the location of the compression of the cord and spinal nerve roots. Symptoms range from pain to loss of sensation or motor function and decreased sensitivity to heat or cold and bowel or ladder dysfunction.

   Laboratory Findings

Evaluation of the CSF reveals increased protein. The level may be very high and is associated with xanthochromia when there is a block of the subarachnoid space. The protein concentration is higher with complete block in cord tumors located at lower levels. Tumor cells may be demonstrable. Definitive diagnosis is made on tissue evaluation at biopsy (see eBook Figure 4-21).

References

1.  Duong LM, McCarthy BJ, McLendon RE, et al. Descriptive epidemiology of malignant and nonmalignant primary spinal cord, spinal meninges, and cauda equina tumors, United States, 2004–2007.
Cancer.
2012;118(17):4220–4227.

2.  Kim MS, Chung CK, Choe G, et al. Intramedullary spinal cord astrocytoma in adults: postoperative outcome.
J Neurooncol.
2001;52:85.

3.  Reimer R, Onofrio BM. Astrocytomas of the spinal cord in children and adolescents.
J Neurosurg.
1985;63:669.

CONGENITAL DISORDERS OF THE CNS

NEURAL TUBE DEFECTS

   Definition

Neural tube defects (NTD) are due to a failure of the closure of the embryonic neural tube. They are second only to cardiac malformations as the cause of congenital anomalies. The supplementation of folic acid for all pregnant women has decreased the incidence of NTD markedly in the United States. Neural tube defects range from the most severe (anencephaly) to mild spinal defects (spina bifida) (see eBook Figure 4-22).

   Clinical Presentation

The risk factors for NTD include folic acid deficiency, certain drugs (valproic acid, carbamazepine, and methotrexate), diabetes, obesity, and hyperthermia. Genetic factors may be associated with NTD, and fetuses with NTD have a high rate of karyotypic abnormalities. Trisomy 18 is the most common chromosomal abnormality found in NTD.
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   Laboratory Findings

Screening for NTD in all pregnant women should include alpha-fetoprotein(AFP) in the maternal serum. Screening should occur between 15 and 20 weeks, and results are expressed as multiples of the median (MoM) for each gestational week. Values >2.0–2.5 MoM are abnormal. AFP is more reliable for open neural tube defects, and the detection rate for anencephaly has been reported as high as 95%.
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Care should be taken in the interpretation of this test as it is affected by gestational age, maternal weight, maternal diabetes, multiple gestation, and race. In addition to laboratory testing, ultrasound is an excellent means for the identification of NTD.

References

1.  Kennedy D, Chitayat D, Winsor EJ, et al. Prenatally diagnosed neural tube defects: ultrasound, chromosome, and autopsy or postnatal findings in 212 cases.
Am J Med Genet.
1998;77:317.

2.  Wang ZP, Li H, Hao LZ, et al. The effectiveness of prenatal serum biomarker screening for neural tube defects in second trimester pregnant women: a meta-analysis.
Prenat Diagn.
2009;29:960.

TRAUMA AND VASCULAR DISORDERS OF THE CNS

CENTRAL NERVOUS SYSTEM TRAUMA