Neoplasms that spread to the CNS
Primary neoplasms of the skull and spine may impinge upon the CNS, and (primary) neoplasms in other organs may metastasize to the CNS, its coverings, or its bony surroundings (Fig. 46.1).
Neoplasms that spread to the CNS, particularly intracerebral and intravertebral metastases, are common. Their reported incidence varies widely, and reflects whether authors have surveyed necropsy data or clinicopathologic data from centers that deal with different aspects of patient care (neurosurgery, radiotherapy, hospice care). The frequency of CNS metastasis also varies according to the site of primary neoplasm (Fig. 46.1).
SECONDARY CNS NEOPLASMS
Account for approximately 15% of intracranial neoplasms (in neurosurgical centers).
Are eventually present in approximately 30% of patients with disseminated cancer.
Present most frequently in the sixth and seventh decades.
Are solitary in approximately 50% of patients.
Are derived most commonly (50% of patients) from primary neoplasms in the lung.
Present before the primary neoplasm in approximately 15% of patients.
NEOPLASMS IN TISSUES SURROUNDING THE CNS
Primary and secondary neoplasms of the skull and spine produce symptoms and signs by destroying bone and compressing nervous system structures, either elements of the CNS or proximal cranial and spinal nerves (Fig. 46.2). Similar problems are caused on the occasions when mediastinal and retroperitoneal neoplasms invade the extradural space around the spinal cord.
Secondary carcinoma is the commonest neoplasm to impinge upon the CNS from surrounding structures, but other types of neoplasm at these sites behave similarly. Diagnosis is facilitated by consideration of the patient’s medical history, assessment of hematologic indices, and a range of imaging studies, in conjunction with histologic examination of biopsies (Figs 46.3–46.5).
46.3 Metastatic carcinoma in the spine.
(a) Multiple deposits of metastatic carcinoma are present in the vertebrae. A tumor mass may extend from the bone to compress the spinal cord, but more commonly the pathology causes collapse of the vertebra, which itself compresses the cord. (b) This shows a vertebral deposit of adenocarcinoma from a primary tumor in the prostate gland, which presented with cord compression. An acinar architecture is evident. Common secondary carcinomas in the spine are from primary sites in the breast, lung, and prostate gland. Prostatic carcinoma that has metastasized to bone is commonly osteoblastic, in contrast to metastases from other carcinomas, which tend to be osteolytic. If the origin of a metastatic carcinoma is unknown, immunohistochemistry should be used, along with imaging studies, to investigate possible primary sites; this tumor was immunoreactive for prostatic specific antigen and prostatic acid phosphatase.
46.4 Plasmacytic lymphoma (plasmacytoma).
(a) This lymphoreticular neoplasm shows plasma cell differentiation and, in this case, was a solitary lesion in the spine, causing local pain and compression of CNS structures. About 50% of solitary osseous plasmacytic lymphomas progress to multiple myeloma, which is the commonest primary neoplasm within bone to cause CNS symptoms. (b) This plasmacytic lymphoma labeled with an antibody to CD79a, a pan-B cell marker. (c) Light chain restriction can sometimes be demonstrated in plasmacytic lymphoma/multiple myeloma by immunohistochemistry. In this case, cells labeled with a λ antibody (as shown here), but not a κ antibody. In situ hybridization for light chain mRNA is an alternative method for demonstrating clonality. (d) Plasmacytic lymphoma may rarely react with antibodies to epithelial membrane antigen (as shown here), leading potentially to an erroneous diagnosis of metastatic carcinoma. Normal plasma cells are immunoreactive for EMA. CD79a antibodies are helpful in this situation because they should not label carcinomas. With low-grade lymphoid neoplasms comprising well differentiated cells, the issue of whether the pathology is neoplastic or inflammatory sometimes arises. In this situation, establishing immunophenotype or the presence of tumor cell clonality will assist the diagnosis, along with other investigations, such as plasma electrophoresis.
46.5 Chordoma.
About 80% of chordomas arise in the sacrum or the clivus, growing slowly into the spinal canal or base of the brain respectively. (a)
