Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Metastatic Disease and the Nervous System
The entire nervous system is potentially vulnerable to metastatic disease, typically occurring in the setting of a known disseminated systemic malignancy. Approximately 45 percent of patients with systemic cancer and neurologic deficits are found to have metastatic involvement of the nervous system. The most common cancer-related neurologic diagnosis is brain metastasis (16%), followed by bone metastasis (10%) and epidural metastasis (9%). The incidence of metastatic involvement of the nervous system continues to rise due to improved treatment strategies directed toward primary cancers and systemic metastases. In 2019, estimated new cancer cases in the United States exceeded 1.7 million.
Metastatic involvement of the central nervous system, including its overlying structures, and the peripheral nervous system causes significant neurologic morbidity and mortality. The skeletal muscles are affected only rarely. Early diagnosis and treatment may prevent disability in these groups of patients, most of whom have a limited life expectancy.
Metastases to the Central Nervous System and Related Structures
Brain
Epidemiology
In the United States between 2010 and 2013, 217,687 out of 1.3 million patients with malignancy were diagnosed with one or more metastases. A total of 26,430 patients, 2 percent of all patients with cancer and 12.1 percent of those with metastatic disease, were found to have brain metastases at diagnosis. The estimated incidence of identified brain metastases among patients with newly diagnosed cancer is 23,598 annually. Patients with small cell and nonsmall cell lung cancer have the highest rate of brain metastasis at the time of cancer diagnosis. Among patients with metastatic disease, patients with melanoma (28.2%), lung adenocarcinoma (26.8%), nonsmall cell lung cancer not otherwise specified/other lung cancer (25.6%), small cell lung cancer (23.5%), squamous cell lung carcinoma (15.9%), bronchioloalveolar carcinoma (15.5%), and renal cancer (10.8%) have the highest incidence proportion of brain metastases. Brain metastases are more common in Hispanics or Asians than other ethnic groups. The incidence of brain metastasis is increasing and this has been related to improvements in systemic therapy and to greater utilization of appropriate imaging studies.
Pathophysiology
The most common mechanism of spread to the brain is hematogenous dissemination. The “anatomic or mechanical” hypothesis states that the distribution of metastases is related to the amount of blood flow to the brain. This phenomenon explains the predilection for brain metastases to involve the cerebral hemisphere in 80 percent, cerebellum in 15 percent, and brainstem in 5 percent of cases. As cancer cells travel through the arterial circulation, they become trapped in the end arteries at the gray–white matter junction ( Fig. 26-1 ). Only about two-thirds of metastases can be explained by blood flow alone, suggesting that other factors play a role. The “seed and soil” mechanism postulates that appropriate tumor cells or “seeds” grow in site-specific hosts or “soil.” Brain metastases are hypothesized to result from neurotropic factors facilitating “brain-homing” and direct interaction with neural substance. The vascular basement membrane of pre-existing blood vessels promotes nonsprouting angiogenesis and proliferation of metastatic tumor cells by means of tumor cell vascular endothelial growth factor (VEGF).
Clinical studies have detected specific genomic mutations present in brain metastases, but not in the primary tumor or in extracranial metastases. In a comprehensive genomic study of matched brain metastases, primary tumors, and normal tissues, over 50 percent of brain metastases had additional targetable mutations that were not found in the matched clinically sampled primary tumors. These additional oncogenic alterations may have driven the proliferation or survival of a prometastatic subclone within the primary tumor, leading to metastases. Contiguous brain invasion from intracranial dural and skull-base metastases is another mechanism by which brain metastases occur.
Pathology
Grossly, metastatic tumors in the brain are well-circumscribed and surrounded by edematous white matter; cystic degeneration, necrosis, and hemorrhage can be seen. Metastatic lesions from melanoma, choriocarcinoma, and renal cell carcinoma have a high tendency for intratumoral hemorrhage. Microscopically, brain metastases are usually well-demarcated and generally appear histologically similar to the primary tumor. Vascular proliferation within the lesions and reactive astrocytosis in the surrounding brain parenchyma may be encountered. Metastases from breast, kidney, and colon are usually solitary, whereas multiple metastases are common from melanoma and lung carcinoma. Molecular genetic analysis can provide information in determining metastatic cancers of unknown origin. Molecular studies also define oncogenic pathways such as in lung cancer (ALK, C-MET, ROS1, RET), breast cancer (Her2/Neu), and melanoma (BRAFV600E, NRAS, CKIT) that can be targeted for therapy.
Clinical Features
Neurologic manifestations in patients with brain metastases may be focal, resulting from local displacement or destruction of the surrounding parenchyma by the tumor or edema, or generalized due to increased intracranial pressure (ICP) or hydrocephalus. Patients usually present with subacute or chronic progressive neurologic signs and symptoms. Headache, typically worse in the morning, is the most common presenting symptom, affecting approximately 50 percent of patients. Focal neurologic deficits are present in 30 to 40 percent of patients, cognitive dysfunction in 30 to 35 percent, and seizures as a presenting feature in 15 to 20 percent. Another 5 to 10 percent of patients present with acute “stroke-like” symptoms due to intratumoral hemorrhage. Nearly 15 percent are asymptomatic.
Over 80 percent of patients diagnosed with brain metastases have a known systemic malignancy (metachronous presentation). In up to 30 percent of patients, brain metastases are diagnosed at the same time as the primary malignancy (synchronous presentation) and in another 5 to 10 percent the brain metastases are the presenting manifestation (precocious presentation). A majority of patients (more than 30%) have multiple metastases with more than four lesions, 20 to 30 percent have two to three lesions (“oligometastases”), and another 20 to 30 percent have a solitary metastasis.
Diagnostic Studies
Magnetic resonance imaging (MRI) is the diagnostic modality of choice for the evaluation and monitoring of patients with brain metastases and is much more sensitive than computed tomography (CT) in detecting the number, size, location, and secondary effects of the lesions. Brain metastases tend to be multiple, spherical, and located at the gray–white matter junction, with surrounding vasogenic edema. These lesions appear isointense or hypointense on precontrast T1-weighted MRI sequences and enhance avidly upon contrast administration due to a disrupted blood–brain barrier. The surrounding edema is hyperintense on T2-weighted and fluid-attenuated inversion recovery sequences ( Fig. 26-1 ). The amount of surrounding edema is often disproportionate to the size of the lesions. Intratumoral hemorrhage within the tumor, when present, is evident on precontrast T1 and gradient recalled echo sequencing ( Fig. 26-2 ). CT studies are generally utilized in acute settings to determine the presence of hemorrhage, herniation, or hydrocephalus. For patients previously treated with radiation, the differentiation of tumor recurrence from radiation effects with routine MRI may be challenging. Increased glucose metabolism with [ 18 F]fluorodeoxyglucose positron emission tomography (FDG-PET) studies is characteristic for brain metastases, whereas lesions composed of radiation necrosis are frequently hypometabolic. Increase in relative cerebral blood volume on MR perfusion imaging may also allow this distinction. MR spectroscopy often shows lower choline-to-creatinine ratio in brain metastases than in high-grade gliomas.
A search for primary malignancy should be performed in patients with suspected brain metastases without a known systemic cancer. CT of the chest takes precedence over abdominal and pelvic evaluation because of the high frequency of brain metastases originating from the lungs. Whole-body FDG-PET is also helpful in investigating the primary source, although it has low specificity in differentiating malignant from benign inflammatory lesions. Biopsy of tumors discovered upon systemic evaluation is often easier than biopsy or resection of the brain lesion.
Differential Diagnosis
Several conditions mimic the radiologic findings of brain metastases including high-grade glioma, lymphoma, abscess, stroke, and demyelinating disorders. Different imaging techniques and special characteristics of the lesions may help distinguish between these clinical entities. An elevated cerebral blood volume in perfusion studies reflects tumor vascularity and is diminished in edema, radiation necrosis, or infarct. MR spectroscopy detects the metabolic characteristics of these lesions, differentiating spectra of metastases, gliomas, vasogenic edema, or gliosis, and other mass lesions. Diffusion-weighted imaging (DWI) detects areas of the brain with decreased proton mobility, while the apparent diffusion coefficient (ADC) characterizes the rate of diffusional motion; unrestricted diffusion in DWI and high ADC value in the center of a ring-enhancing mass are suggestive of a necrotic mass as seen in metastasis or high-grade glioma. Restricted diffusion represents cytotoxic edema in an acute infarct, and is also seen in highly cellular lesions such as cerebral abscess, infectious encephalitis, or primary CNS lymphoma. In many cases, brain biopsy is required for definitive diagnosis.
Prognostic Variables
Classifying patients with brain metastases based on prognosis helps clinicians maximize survival while avoiding unnecessary treatments. Important factors that predict outcomes are age, performance status, status of primary tumor, and extent of extracranial disease. The Radiation Therapy Oncology Group used recursive partitioning analysis (RPA) to categorize patients into three prognostic classes. Patients harboring all four favorable prognostic factors [age less than 65 years, Karnofsky performance status (KPS) of at least 70, controlled primary tumor, and no extracranial metastases] had the best prognosis, with expected median survival of 7.1 months. Patients with KPS of 70 or more but at least one other unfavorable factor have an intermediate prognosis, with expected median survival of 4.2 months. A KPS of less than 70 is a poor-prognostic factor, with median survival of 2.3 months ( Table 26-1 ). Important prognostic factors also vary depending on tumor type. KPS, number of brain metastases, extracranial metastasis, and hemoglobin are important prognostic factors for renal cell carcinoma. The updated Disease-Specific Graded Prognostic Assessment (DS-GPA) which incorporated gene and molecular alteration data with clinical factors identified KPS, age, presence of extracranial metastases, number of brain metastases, and the presence of EGFR or ALK gene alterations for lung cancer and BRAF status for melanoma as significant prognostic factors, whereas in breast cancer, the hormonal status (estrogen receptor and progesterone receptor), human epidermal growth factors receptor (EGFR) 2 status, KPS, and age are important factors, but not the number of brain metastases or status of systemic disease.
Table 26-1
Recursive Partitioning Analysis (RPA) Categorization of Patients into Three Prognostic Classes
Further details are provided by Gaspar LE, Scott C, Murray K, et al: Validation of the RTOG recursive partitioning analysis (RPA) classification for brain metastases. Int J Radiat Oncol Biol Phys 47:1001, 2000.
| RPA Class | Factors | Median Survival |
|---|---|---|
| 1 |
|
7.1 months |
| 2 | All patients not in class 1 or 3 | 4.2 months |
| 3 | KPS <70 | 2.3 months |
KPS, Karnofsky performance status.
Treatment
Management includes supportive care for palliation of symptoms and definitive treatment directed toward the metastases, aiming to prolong survival while preserving quality of life. Most patients die from their systemic disease rather than from their metastases.
Supportive Treatment
Dexamethasone is the corticosteroid of choice in controlling vasogenic edema, as it has a long half-life, the best CNS penetration, the fewest mineralocorticoid side effects, and is the least protein bound. The recommended starting dose is 4 to 8 mg daily for symptomatic patients, and this can be increased to 16 to 32 mg daily for patients presenting with acute signs of increased ICP or with severe symptoms. Its therapeutic effects are usually evident within 24 to 72 hours in up to 75 percent of patients. Once clinical benefit occurs, dexamethasone should be titrated down to the lowest possible dose that provides relief of symptoms, in order to minimize adverse effects. Prophylactic treatment for peptic ulcers is generally not recommended, except for patients with a history of previous ulcer, those taking concurrent nonsteroidal anti-inflammatory drugs, or the elderly. Among patients with brain metastases, 20 percent experience seizures, and antiepileptic drugs (AEDs) should be given when they occur. Older AEDs such as phenytoin, phenobarbital, and carbamazepine induce cytochrome P-450 hepatic enzymes, which potentially can accelerate the metabolism of many chemotherapeutic agents. Because of these drug interactions, nonenzyme-inducing AEDs such as levetiracetam are preferable. Evidence has failed to show benefit of prophylactic AEDs in decreasing the incidence of new-onset seizures, and therefore prophylaxis is not recommended. The benefit for prophylactic AEDs in the perioperative period has not been proven; when AEDs are utilized in this manner, they should be discontinued 1 to 2 weeks postoperatively.
Surgery
Resection of brain metastases is performed to achieve local disease control, provide a histologic diagnosis, promote decompression from elevated ICP, and allow tapering of corticosteroids. Three randomized controlled trials have examined the benefit of surgery combined with whole-brain radiation therapy (WBRT) compared to WBRT alone in patients with a solitary brain metastasis; a fourth randomized trial compared both treatments to surgery alone. These studies demonstrated significant benefits in local disease control and prolongation of functional independence from combination treatment compared to resection or radiotherapy alone, when given to patients with a single metastasis who were 60 years old or less and had controlled systemic disease and good KPS ( Table 26-2 ). For patients with more than one metastasis, surgery is generally limited to removal of the dominant, life-threatening lesion, and to obtain a histologic diagnosis.
Table 26-2
Randomized Controlled Trials of Patients with Single Brain Metastasis Treated With Surgery, Radiotherapy, or Both
Data from *Patchell RA, Tibbs PA, Walsh JW, et al: A randomized trial of surgery in the treatment of single metastases to the brain. N Engl J Med 322:494, 1990; ¶ Vecht CJ, Haaxma-Reiche H, Noordijk EM, et al: Treatment of single brain metastasis: radiotherapy alone or combined with neurosurgery? Ann Neurol 33:583, 1993; ¥ Mintz AH, Kestle J, Rathbone MP, et al: A randomized trial to assess the efficacy of surgery in addition to radiotherapy in patients with a single cerebral metastasis. Cancer 78:1470, 1996; § Patchell RA, Tibbs PA, Regine WF, et al: Postoperative radiotherapy in the treatment of single metastases to the brain: a randomized trial. JAMA 280:1485, 1998.
| Population Studies | Median Survival | Duration of Functional Independence | ||||
|---|---|---|---|---|---|---|
| Test Group | Standard | Result | Test Group | Standard | Result | |
| Surgery+WBRT vs. WBRT* | 40 weeks | 15 weeks | S | 38 weeks | 8 weeks | S |
| N =48 | ||||||
| Surgery+WBRT vs. WBRT ¶ | 12 months | 7 months | S | 9 months | 4 months | S |
| N =63 | ||||||
| Surgery+WBRT vs. WBRT ¥ | 5.6 months | 6.3 months | NS | – | – | – |
| N =84 | ||||||
| Surgery+WBRT vs. Surgery § | 48 weeks | 43 weeks | NS | 37 weeks | 35 weeks | NS |
| N =95 | ||||||
WBRT, whole-brain radiotherapy; S, significant; NS, not significant.
Whole-Brain Radiotherapy
Treatment with WBRT targets both gross and microscopic metastases. Significant reduction of local and remote intracranial recurrence has been demonstrated in patients with solitary and oligometastases who received WBRT following surgical resection or stereotactic radiosurgery; however, overall survival and preservation of functional independence did not differ between those treated with or without adjuvant WBRT. An individual patient data meta-analysis of three randomized trials assessing stereotactic radiosurgery with or without WBRT demonstrated a survival advantage for stereotactic radiosurgery alone in patients with one to four brain metastases, KPS of 70 or higher, and age of 50 or younger. Furthermore, in this cohort, no apparent increased risk of new brain metastases was observed, supporting stereotactic radiosurgery alone in patients with up to four brain metastases in this age group. In older patients (>50 years old), WBRT decreased the risk of new brain metastases, but did not affect survival. A phase III trial randomizing patients with one to three brain metastases to stereotactic radiosurgery alone or followed by WBRT demonstrated a more frequent neurocognitive decline in patients who received WBRT after stereotactic radiosurgery without significant difference in survival. For patients with multiple metastases not amenable to surgery or stereotactic radiosurgery, or patients with poor-prognostic factors and limited life expectancy, WBRT is used for palliation of symptoms, prolonging overall survival for up to 3 to 6 months. A phase III randomized trial (QUARTZ) demonstrated that optimal supportive care (OSC) is as effective as OSC with WBRT in patients with nonsmall cell lung cancer with brain metastases unsuitable for surgery or stereotactic radiosurgery. Because of the lack of significant benefit in overall survival and reported neurocognitive toxicity, it is recommended to withhold WBRT after local control with either surgery or stereotactic radiosurgery. The addition of memantine and hippocampal avoidance with WBRT may reduce the risk of neurocognitive decline without a significant difference in intracranial progression-free survival and overall survival.
Stereotactic Radiosurgery
Stereotactic radiosurgery is focused radiotherapy in which high-dose, single-fraction irradiation is directed at metastases while sparing the surrounding normal brain tissues from radiation exposure. It can be delivered by linear accelerator or gamma knife. It is beneficial in treating lesions less than 3 cm in size that are located in the eloquent areas, in the deep structures of the brain, or both, when these are not amenable to surgery. Hypofractionated radiosurgery (2 to 5 fractions of smaller doses) is used for larger metastases to decrease the risk of radionecrosis. The risk of radiation-induced neurocognitive dysfunction is markedly less than with WBRT. Retrospective studies comparing surgery and stereotactic radiosurgery report similar outcome. Therefore, the choice between surgery and stereotactic radiosurgery for local control depends on the number, location, and size of brain metastases, neurologic symptoms, and patient and physician preferences.
For patients with unresectable solitary or oligometastases with good prognostic factors (RPA class I), stereotactic radiosurgery following WBRT confers better local control of lesions and stabilization or improvement of performance status compared to WBRT alone, but survival advantage has been demonstrated only in patients with a single metastasis. The addition of stereotactic radiosurgery to WBRT seems in fact to confer survival benefit for patients with a good prognosis regardless of whether they have one, two, or three brain metastases; however, the survival benefit does not extend to patients with a poor prognosis. Randomized controlled trials comparing stereotactic radiosurgery alone or followed by WBRT showed improved local and remote intracranial control with combined treatment, without significant difference in overall survival and performance status. Based on these randomized trials, close monitoring without WBRT following stereotactic radiosurgery is recommended for patients with one to four brain metastases and good performance status.
Postoperative stereotactic radiosurgery is another approach to decrease the risk of local recurrence while avoiding the neurocognitive toxicity from WBRT. A phase III randomized trial concluded that stereotactic radiosurgery to the surgical cavity results in improved cognitive outcome, better preservation of quality of life and functional independence compared to postsurgery WBRT, without significant difference in overall survival. Stereotactic radiosurgery should be considered one of the standards of care as a less toxic alternative to WBRT after resection of a brain metastasis.
Chemotherapy
Chemotherapy is recommended as first-line treatment for chemosensitive brain metastases such as germ cell tumors and non-Hodgkin lymphoma. Response rates to cytotoxic chemotherapy are high in small cell lung cancer (30 to 80%), intermediate rates in breast cancer (30 to 50%) and nonsmall cell lung cancer (10 to 30%), and low rates in melanoma (10 to 15%); responses in the brain do not always parallel those of systemic disease. Treatment response is higher for chemotherapy-naïve tumors, but as most of these patients have already failed previous chemotherapy, radiotherapy is a more effective option in the treatment of brain metastases. Various chemotherapeutic agents in combination with two or three other agents and radiation therapy have been used ( Table 26-3 ).
Table 26-3
Evolving Systemic Treatment Options for Brain Metastases From Three Common Malignancies
| Malignancies | Agents |
|---|---|
| Cytotoxic Chemotherapies | |
|
|
| Targeted therapies | |
|
|
| Immunotherapies | |
|
|
NSCLC, Nonsmall cell lung cancer; EGFR-TKI, epidermal growth factor receptor-tyrosine kinase inhibitor; ALK, anaplastic lymphoma kinase; CDK, cyclin-dependent kinase; ADC, antibody–drug conjugate; PD1, programmed death receptor 1; CTLA4, cytotoxic T-lymphocyte-associated protein 4; MEK, mitogen-activated protein kinase.
Targeted Therapies
Molecular targeted therapies have shown promising roles in the treatment of brain metastases, including gefitinib, erlotinib, afitinib and osimertinib [epidermal growth factor receptor (EGFR) inhibitors] and crizotinib (ALK and ROS1 inhibitor) for nonsmall cell lung cancer; lapatinib (EGFR and HER2 inhibitors) for HER2-positive breast cancer; and dabrafenib and vemurafenib (BRAF inhibitor) and trametinib (MEK inhibitor) for melanoma ( Table 26-3 ).
Immunotherapy
Immunotherapy has shown promising results in treating brain metastases. Emerging data suggest that immune checkpoint inhibitors (ICI) can stimulate T cells peripherally, resulting in antitumor effects in the central nervous system. ICI blocking programmed cell death protein 1 (PD-1) and its ligand (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) have shown efficacy in brain metastases ( Table 26-3 ). Pembrolizumab (anti-PD1) monotherapy has shown intracranial response rates of 20 to 30 percent in patients with melanoma and nonsmall cell lung carcinoma; while combination of nivolumab (anti-PD-1) and ipilimumab (anti-CTLA-4) has demonstrated an intracranial response in 55 percent of patients with brain metastases from melanoma. Radiation therapy with immunotherapy augments antitumor immune responses at a local site as well as at distant metastatic site, known as the abscopal phenomenon.
Prophylactic Cranial Irradiation
In malignancies with a high predilection to metastasize to the brain such as small cell lung cancer (SCLC), prophylactic cranial irradiation (PCI) may be used. Patients with limited-stage SCLC who achieve complete response to chemotherapy have a decreased incidence of brain metastases (relative risk 0.46; 95% CI 0.38 to 0.57) and absolute decrease in 3-year cumulative incidence of brain metastases (33% vs. 59%) with PCI. However, while PCI can decrease the incidence of symptomatic brain metastases in extensive-stage SCLC, the impact of PCI on overall survival is uncertain due to differences in the results between two phase III randomized trials. Thus, individualized discussion is recommended in patients with extensive-stage SCLC due to the risk of radiation-induced side effects and insufficient evidence on survival benefit of PCI. This prophylactic strategy has not shown the same degree of benefit in NSCLC.
Skull Base
Definition and Epidemiology
The base of the skull forms the floor of the cranial cavity and is composed of the ethmoid, sphenoid, occipital, paired frontal, and paired parietal bones. Metastases to the skull base may involve the cranial nerves and blood vessels that pass through foramina in these bones. Skull-base metastases occur in 4 percent of cancer patients, frequently late in the course of the disease. The most common responsible primary malignancies are prostate (38.5%), breast (20.5%), lymphoma (8%), and lung (6%).
Pathophysiology
The skull base may become involved directly from hematogenous spread of malignant cells or by retrograde seeding through the Batson plexus, a common route in prostate carcinoma. Osseous metastases may entrap and compress the nearby cranial nerves and vessels, producing neurologic signs and symptoms. Direct extension from head and neck malignancies may also involve the skull base.
Clinical Features
Skull-base metastases produce symptoms when they enlarge and compress surrounding structures, causing pain and neurologic deficits. The development of cranial neuropathies or craniofacial pain in patients with malignancy should raise the suspicion of skull-base metastases. Cranial neuropathies are the presenting symptom in 28 percent of patients with such metastases. The extraocular motor nerves are most commonly involved, followed by the trigeminal and hypoglossal nerves. The anatomic location involved can lead to specific clinical syndromes, including orbital syndrome in 12.5 percent, parasellar and sellar syndromes in 29 percent, middle fossa syndromes in 6 percent, jugular foramen syndromes in 3.5 percent, and occipital condyle syndrome in 16 percent of patients ( Table 26-4 ).
Table 26-4
Skull-Base Syndromes, Associated Cranial Neuropathies, Accompanying Findings, and Most Common Primary Malignancies
Derived from Harrison RA, Nam JY, Weathers SP, et al: Intracranial dural, calvarial, and skull base metastases. Handb Clin Neurol 149:205, 2018.
| Skull-Base Syndromes | Cranial Neuropathies | Associated Findings | Common Primary Malignancies |
|---|---|---|---|
| Orbital syndrome | CN II, III, IV, VI, and V-1 | Supraorbital frontal headache, pain, diplopia, proptosis, periorbital swelling, decreased vision | Prostate cancer Lymphoma Breast cancer |
| Parasellar/cavernous sinus syndrome | CN III, IV, VI, V-1, and V-2 | Supraorbital frontal headache, no proptosis, vision may be affected late in the course | Lymphoma |
| Middle fossa/Gasserian ganglion syndrome | CN V-2 and V-3 sensory and motor roots; CN III, IV, VI, and VII (less common) | Lightning-like facial pain, sparing the forehead; headache is uncommon | Breast cancer Lung cancer |
| Jugular foramen syndrome | CN IX, X and XI (Vernet syndrome) plus CN XII (Collet–Sicard syndrome) | Unilateral occipital and postauricular pain; dysphagia; hoarseness; Horner syndrome | Breast cancer Melanoma Ewing sarcoma Prostate cancer |
| Occipital condyle | CN XII | Occipital pain, stiff neck | Breast cancer Prostate cancer |
| Numb chin syndrome | Mental nerve | Unilateral anesthesia of chin and lower lip | Breast cancer Lymphoma Melanoma Lung cancer Prostate cancer |
Diagnostic Studies
Advances in MRI techniques have greatly improved the identification and evaluation of the extent of skull-base metastases, including bone marrow invasion, perineural spread, and cranial nerve, leptomeningeal, and brain parenchymal involvement ( Fig. 26-3 ). Radionuclide bone scanning can detect skull-base metastases in 30 to 50 percent of these patients, but it has a relatively poor sensitivity in detecting purely lytic lesions. CT using bone windowing is the best means of detecting lytic bone destruction. Dual-isotope single-photon emission computed tomography (SPECT) may show increased uptake in the skull base. CSF examination and biopsy, including endoscopic and minimally invasive techniques, are sometimes indicated to establish the diagnosis of skull-base metastases.
Differential Diagnosis
Primary skull tumors, such as osteoma and chondrosarcoma, and benign tumor-like lesions including fibrous dysplasia may appear radiographically similar to skull-base metastases. Patients with metastases are generally older, with a median age of 70 years, have shorter duration of symptoms (median of 2 months), and present less frequently with neurologic deficits than patients with these other lesions.
Treatment
Radiation therapy is the standard treatment, providing pain relief, improvement of cranial nerve dysfunction and local control. The beneficial effects parallel the timing of irradiation—87 percent of patients who receive radiation within 1 month of symptom onset show clinical improvement compared with 25 percent of patients treated after 3 months. Stereotactic radiosurgery provides clinical improvement in 62 percent and tumor control in 67 to 95 percent of patients, and can be used as an initial treatment, especially for lesions near neural structures and for previously irradiated tumors. For chemosensitive tumors such as breast and prostate carcinomas, chemotherapy and hormonal therapy in combination with radiation therapy offer survival benefits. Surgery may be considered for radioresistant tumors such as melanoma, renal cell carcinomas, and sarcomas, as well as in patients with rapid neurologic decline, such as visual loss, with the goal of preserving neurologic status and symptom relief.
Prognosis
Skull-base metastases are typically seen in disseminated malignancies, and the overall median survival is 31 months. Patients with metastases from breast carcinoma have the best survival (60 months); prostate carcinoma and lymphoma, intermediate survival; and lung and colon carcinomas the worst survival (2.5 and 2.1 months, respectively).
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here