• Typically secondary to hematogenous dissemination
• Lung, breast, melanoma, renal, and colorectal cancer represent the most common primary sites
• Although less common, parenchymal metastases can arise in the setting of direct extension from head and neck primary tumors
• Gross specimen appears as round, circumscribed, tan or grayish-white nodules
• Associated features, including hemorrhage, peritumoral edema, necrosis, and mucinous material, and specific histology vary depending on the primary tumor

• Symptoms
  • Presenting symptoms are highly variable, ranging from asymptomatic (up to 75% of the time) to severe neurological deficits
  • Patients with symptoms typically present with headache, seizure, and/or focal neurological deficits
  • Specific neurological deficits directly related to the particular anatomic site of parenchymal metastases
• Prognosis
  • Parenchymal metastatic disease overall portends a very poor outcome
  • Detection of parenchymal metastases is of critical clinical importance, because treatment strategy often drastically changes based on presence of metastatic disease

• General
  • Parenchymal metastases typically located at the gray–white junction
  • Majority occur within the cerebral hemispheres (80%), with the cerebellum (15%) and basal ganglia (3%) less commonly involved
  • A few primary malignancies, however, such as uterine and prostate cancer, may show predilection for the posterior fossa
  • Parenchymal metastases can be solitary (50%), occur as 2 lesions (20%), or present as 3 or more lesions (30%)
  • Variable size; most are <1.5 cm
• Modality specific
  • CT
    • Predominant feature of parenchymal metastases is marked surrounding vasogenic edema (white matter hypodensity abutting adjacent peripheral gray matter) and can be the only visible feature
    • Majority of metastases, if visualized, are hypodense to isodense relative to adjacent brain parenchyma
    • Metastases with a high nuclear-to-cytoplasmic ratio can appear hyperdense
    • Associated hyperdense hemorrhage can be seen, particularly with melanoma, thyroid, renal cell, choriocarcinoma, and breast primaries
    • Avid enhancement is a typical feature on contrast-enhanced CT imaging
  • MRI
    • T1WI
      • Metastases are usually mildly hypointense to isointense on T1WI
      • Exceptions include T1 hyperintense melanotic melanoma metastases and hemorrhagic metastases with variably increased signal depending on the age of the blood products
    • T2WI/FLAIR
      • Typically T2 hyperintense, although tumors with a high nuclear-to-cytoplasmic ratio can be hypointense
      • Associated vasogenic edema appears as white matter T2/FLAIR hyperintensity surrounding metastasis
    • DWI
      • Parenchymal metastases have variable appearance on DWI, with high-cellularity tumors more likely to show restricted diffusion (high DWI/low ADC signal)
    • SWI
      • Melanoma and hemorrhagic metastases appear as low signal “blooming” on SWI
    • Contrast
      • Most parenchymal metastases demonstrate avid enhancement, particularly compared to the surrounding brain parenchyma with its intact blood–brain barrier
      • Enhancement patterns are usually solid, nodular, or ring-enhancing
• Imaging recommendations
  • Modality of choice depends on the clinical scenario and the acuity of symptoms
  • Noncontrast CT is often performed in emergent situations to evaluate for hemorrhage and to assess sequelae of mass effect
  • If nonemergent, MRI without and with intravenous contrast is the preferred imaging modality for completely characterizing the extent of metastatic disease and monitoring for treatment response or progression
• Mimics
  • Infectious
    • Focal nodular and ring-enhancing lesions at the gray–white junction also often seen with infectious etiologies, such as cerebral abscesses and septic emboli
    • Central restricted diffusion more commonly seen with abscesses/emboli
  • Neoplastic
    • Solitary metastases in particular can be difficult to differentiate from primary central nervous system neoplasms such as glioblastoma
    • Glioblastomas more likely centered in deep white matter and demonstrate infiltrative appearance versus the demarcated appearance and peripheral gray–white location of metastases
  • Demyelinating
    • Demyelinating lesions, such as in patients with multiple sclerosis, more likely to be located in deep and periventricular white matter
    • Incomplete ring enhancement is classic pattern for demyelinating lesions
  • Ischemic
    • Small subacute strokes might enhance, mimicking metastatic lesion
    • Enhancement pattern with ischemia more likely to be nodular or ring-enhancing

• Typically occurs in setting of direct extension from adjacent calvarial metastases
• Additional proposed mechanisms include retrograde seeding through valveless vertebral venous plexus, hematogenous dissemination, and lymphatic seeding
• Most common primary sites include breast, prostate, head and neck, lung, and hematologic malignancies
• Dural metastases appear as focal nodules or plaquelike sheets

• Symptoms
  • Range from asymptomatic, with dural metastases incidentally discovered on imaging, to those with significant neurological symptoms
  • Patients with symptoms typically present with headaches, cranial neuropathy, seizures, altered mentation, and/or visual disturbances
• Prognosis
  • Presence of dural metastatic disease forebodes a poor prognosis with most patients eventually demonstrating disease progression
  • Disease progression typically manifests as local dural progression, distant dural spread, and leptomeningeal or intraparenchymal extension

• General
  • Dural metastases involve dura-arachnoid immediately subjacent to the calvarium
  • May occur from direct extension from an adjacent calvarial metastasis or hematogenous spread
  • Presence of single dura-based metastasis usually due to extension from calvarial metastatic disease
  • Most commonly, hematogenous spread to the dura presents as multiple dura-enhancing lesions
• Modality specific
  • CT
    • Limited assessment for dura-based metastases
    • Bone algorithm helpful for evaluating presence of associated calvarial metastases
  • MRI
    • T1WI
      • Focal nodular or diffuse dural thickening with usually hypointense or isointense signal relative to adjacent cortex
      • Associated calvarial metastases are T1 hypointense, replacing the normal bright marrow fat
    • T2WI/FLAIR
      • Dural metastases have variable T2/FLAIR signal
      • T2/FLAIR hyperintensity of the adjacent brain parenchyma can occur with presence of vasogenic edema secondary to compression, direct invasion, or impaired venous drainage
    • DWI
      • High-cellularity metastases can show restricted diffusion (high DWI/low ADC signal)
    • Contrast
      • Foci of dural thickening demonstrate avid enhancement
      • Enhancement pattern can be smooth, nodular, or a combination of both
• Imaging recommendations
  • Modality of choice depends on the clinical scenario and the acuity of symptoms
  • Noncontrast CT is often performed in emergent situations
  • If nonemergent, MRI without and with intravenous contrast is the preferred imaging modality
• Mimics
  • Meningioma
    • Focal dural metastasis can have an essentially identical appearance to a meningioma on imaging
    • Presence of associated skull metastasis and bony erosive changes and parenchymal lesions suggest metastatic disease
    • Previous imaging very helpful for evaluating stability
  • Diffuse dura-arachnoid thickening
    • Many nonneoplastic processes can result in diffuse pachymeningeal thickening, such as chronic subdural hematomas, intracranial hypotension, autoimmune dural thickening, and infectious meningitis
    • Clinical context is often of critical importance

• Often occur secondary to hematogenous dissemination; breast cancer, lung cancer, and melanoma represent the most common primary tumor types
• Leptomeningeal metastases from intracranial primary tumors
  • In adults, most commonly seen with glioblastoma
  • In children, most commonly seen with medulloblastoma and other embryonal tumors
• Multifocal tumoral deposits coating the pia mater and filling the subarachnoid spaces

• Symptoms
  • Highly variable depending on particular site of involvement
  • Typical general symptoms include headache, confusion, nausea, and vomiting
  • Cranial and spinal neuropathies are common, with diplopia, facial weakness, and hearing impairment frequent symptoms secondary to involvement of cranial nerves VI, VII, and VIII (abducens, facial, and vestibulocochlear nerves)
• Prognosis
  • Leptomeningeal metastatic disease portends a poor prognosis; average survival, 2 to 4 months

• General
  • Leptomeningeal metastases involve the subarachnoid spaces and pial layer along the parenchymal surface following the gyri and sulci
  • Hydrocephalus can be present as a complication of leptomeningeal metastatic debris or secretions obstructing at the level of the arachnoid granulations
• Modality specific
  • CT
    • Often normal but may see hydrocephalus and subtle effacement of the cerebral sulci and cisterns
    • With more pronounced involvement, can see enhancement of the cerebral sulci and cisterns
  • MRI
    • T1WI
      • Often normal, but subtle increased signal in the cerebral sulci might be seen
    • T2WI/FLAIR
      • Leptomeningeal metastases often similar in signal to cerebrospinal fluid (CSF) on T2WI
      • Unlike CSF, leptomeningeal metastases will not lose signal on FLAIR, resulting in increased signal within the sulci and cisterns
    • Contrast
      • Postcontrast T1WI will demonstrate miliary, sheet-like, or nodular enhancement of the leptomeninges resulting in enhancement of the sulci and cisterns
      • Contrast-enhanced T2 FLAIR imaging
        • Highly sensitive for detection of leptomeningeal metastases
        • Demonstrates hyperintense “enhancement” in the involved CSF spaces due to incomplete CSF signal suppression
• Imaging recommendations
  • Modality of choice depends on clinical scenario and acuity of symptoms
  • Noncontrast CT often performed in emergent situations
  • If nonemergent, MRI without and with intravenous contrast is the preferred imaging modality
• Mimics
  • Diffuse leptomeningeal thickening and enhancement
    • Many nonneoplastic processes can demonstrate diffuse leptomeningeal thickening and enhancement, such as infectious meningitis and neurosarcoidosis
    • Clinical context, history, and CSF analysis are critical for distinguishing etiologies, although CSF analysis is often falsely negative for leptomeningeal disease
  • Diffusely increased signal within the subarachnoid spaces on FLAIR; many conditions can contribute to diffusely increased signal within the sulci on FLAIR, mimicking diffuse leptomeningeal metastatic disease
    • Propofol for anesthesia
    • Hyperoxygenation
    • Previous intravenous gadolinium administration
    • Subarachnoid hemorrhage
    • Infectious meningitis
  • Clinical context and history critical for distinguishing etiologies

• Typically secondary to hematogenous spread to the choroid plexus
• Lung and kidney represent the most common primary sites in adults, whereas neuroblastoma, Wilms tumor, and retinoblastoma are the most common etiologies in children

• Intraventricular metastases are relatively uncommon, representing only 0.9% to 4.6% of cerebral metastases
• Symptoms
  • Intraventricular neoplasms in general result in various presentations based on particular location
  • Nausea, vomiting, and headache are more likely in the setting of hydrocephalus and elevated intracranial pressure
• Prognosis
  • Presence of intraventricular metastatic disease generally indicates a poor prognosis

• General
  • Mass-like enlargement of the choroid plexus
  • Involvement is most common in the lateral ventricle and second most common in the third ventricle
  • Choroid plexus metastases are often hemorrhagic
• Modality specific
  • CT
    • Isodense to hyperdense enlargement of the choroid plexus
    • Avid, heterogeneous enhancement post-contrast
  • MRI
    • T1WI
      • Usually hypointense on T1WI
      • Variable signal with hemorrhagic metastases
    • T2WI/FLAIR
      • Typically T2/FLAIR hyperintense
      • Might show edema of the adjacent brain parenchyma
    • SWI
      • Hemorrhagic metastases demonstrate hypointense signal on SWI
    • Contrast
      • Avid, heterogenous enhancement
• Imaging recommendations
  • Modality of choice depends on the clinical scenario and on the acuity of symptoms
  • Noncontrast CT is often performed in emergent situations
  • If nonemergent, MRI without and with intravenous contrast is the preferred imaging modality
• Mimics
  • Choroid plexus/intraventricular metastases are often indistinguishable from intraventricular meningiomas and from primary choroid plexus papillomas and carcinomas
  • Age of the patient and presence of a known primary malignancy should influence concern for metastatic disease
  • Previous imaging very helpful for documenting stability of nonmetastatic lesions

• Occurs most commonly from hematogenous spread of extracranial malignancies, with lung (most common), breast, kidney, and gastrointestinal tract representing the most common primary sites

• Symptoms
  • Pineal neoplasms in general result in symptoms arising from mass effect on nearby structures
  • Compression of the tectal plate can result in Parinaud syndrome (vertical gaze paralysis, pupillary dysfunction, blepharospasm)
  • Obstruction of cerebral aqueduct contributes to hydrocephalus and increased intracranial pressure with headache, nausea, and vomiting

• General
  • Mass involving the pineal gland
  • Often solitary without additional intracranial metastases
  • Variable appearance on CT and MR images but likely to demonstrate avid enhancement
  • Associated obstructive hydrocephalus commonly seen
• Imaging recommendations
  • Modality of choice depends on clinical scenario and acuity of symptoms
  • Noncontrast CT often performed in emergent situations
  • If nonemergent, MRI without and with intravenous contrast is the preferred imaging modality to completely characterize the extent of metastatic disease and to monitor for treatment response or progression
• Mimics
  • Pineal metastases having similar imaging characteristics of other primary pineal neoplasms (eg, pineoblastoma or pineocytoma), making clinical history of critical importance

• Usually occurs secondary to hematogenous spread of extracranial primary malignancies, with breast and lung representing the most common primary sites

• Symptoms
  • Patients often present with diabetes insipidus due to predilection for metastases to involve the posterior pituitary lobe and infundibulum
  • Anterior hypopituitarism can also occur, although it is less likely
  • Visual deficits can be seen secondary to compression of the optic chiasm

• General
  • Sellar-based mass with variable associated mass effect on adjacent suprasellar or parasellar structures, such as the optic chiasm, and with bony changes
  • Predilection for local invasion and rapid growth
• Modality specific
  • CT
    • May see erosive bony changes of the sella turcica
  • MRI
    • Sella-based mass with usually avid enhancement
    • Can have thickening and enhancement of the infundibulum
    • Often have loss of normal T1 bright spot of the posterior pituitary
    • Can see cavernous sinus invasion
• Imaging recommendations
  • Modality of choice depends on clinical scenario and acuity of symptoms
  • Noncontrast CT often performed in emergent situations
  • If nonemergent, MRI without and with intravenous contrast is the preferred imaging modality
  • Dynamic sella protocol MRI could be helpful
• Mimics
  • Pituitary and infundibular metastases can be difficult to distinguish from other primary neoplastic processes such as a macroadenoma, and nonneoplastic processes such as sarcoidosis and lymphocytic hypophysitis
  • Presence of diabetes insipidus and rapid growth are more suggestive of metastasis
  • Clinical context and presence of known systemic malignancy are of critical importance

Contributor: Benjamin Gray, MD

DOI: https://doi.org/10.18791/nsatlas.v1.03.01.29