1 Brain and Extra-axial Lesions(Table 1.5 – Table 1.6)

10.1055/b-0034-75769

1 Brain and Extra-axial Lesions(Table 1.5 – Table 1.6)

**Table 1.5 Extra-axial lesions in the posterior cranial fossa (infratentorial)**
Lesions	CT Findings	Comments
Neoplastic
Metastatic tumor Fig. 1.94a, b Fig. 1.95	Single or multiple well-circumscribed or poorly defined lesions involving the skull, dura, leptomeninges, and/or choroid plexus; low to intermediate attenuation, usually with contrast enhancement, with or without bone destruction, with or without compression of neural tissue or vessels. Leptomeningeal tumor often best seen on postcontrast images.	Metastatic tumor may have variable destructive or infiltrative changes involving single or multiple sites of involvement.
Schwannoma (neurinoma): acoustic, trigeminal, etc. Fig. 1.96 Fig. 1.97a, b	Circumscribed or lobulated extra-axial lesions, low to intermediate attenuation, with contrast enhancement. Attenuation and contrast enhancement can be heterogeneous in large lesions.	Acoustic (vestibular nerve) schwannomas account for 90% of intracranial schwannomas and represent 75% of lesions in the cerebellopontine angle cisterns; trigeminal schwannomas are the next most common intracranial schwannomas, followed by facial nerve schwannomas and multiple schwannomas seen with neurofibromatosis type 2.
Meningioma Fig. 1.98a, b Fig. 1.99a, b	Extra-axial dural-based lesions, well-circumscribed; supra- > infratentorial; intermediate attenuation signal, usually with contrast enhancement, with or without calcifications.	Most common extra-axial tumors, usually benign neoplasms, typically occur in adults (older than 40 y), women > men; multiple meningiomas seen with neurofibromatosis type 2; can result in compression of adjacent brain parenchyma, encasement of arteries, and compression of dural venous sinuses; rarely invasive/malignant types.
Hemangiopericytoma	Extra-axial mass lesions, often well circumscribed; intermediate attenuation, with contrast enhancement (may resemble meningiomas), with or without associated erosive bone changes.	Rare neoplasms in young adults (men > women) sometimes referred to as angioblastic meningioma or meningeal hemangiopericytoma; arise from vascular cells/pericytes; frequency of metastases > meningiomas.
Paraganglioma glomus jugulare Fig. 1.100a–c	Extra-axial mass lesions located in jugular foramen, often well circumscribed; intermediate attenuation, with contrast enhancement; often associated with erosive bone changes and expansion of jugular foramen.	Lesions, also referred to as chemodectomas, arise from paraganglia in multiple sites in the body and are named accordingly (glomus jugular, tympanicum, vagale, etc.).
Choroid plexus papilloma or carcinoma Fig. 1.101a, b Fig. 1.102a, b	Circumscribed and/or lobulated lesions with papillary projections, intermediate attenuation, usually prominent contrast enhancement, with or without calcifications. Locations: atrium of lateral ventricle (children) > fourth ventricle (adults), rarely other locations such as third ventricle. Associated with hydrocephalus.	Rare intracranial neoplasms. CT features of choroid plexus carcinoma and papilloma may overlap; both histologic types can disseminate along CSF pathways. Carcinomas tend to be larger, have greater degrees of mixed/heterogeneous attenuation than papillomas. Carcinomas often show invasion of adjacent brain, whereas papillomas often do not.
Lymphoma	Single or multiple well-circumscribed or poorly defined lesions involving the skull, dura, and/or leptomeninges; low to intermediate attenuation usually with contrast enhancement, with or without bone destruction. Leptomeningeal tumor often best seen on postcontrast images.	Extra-axial lymphoma may have variable destructive or infiltrative changes involving single or multiple sites of involvement.
Neurocutaneous melanosis	Extra- or intra-axial lesions usually > 3 cm in diameter with irregular margins in the leptomeninges or brain parenchyma/brainstem (anterior temporal lobes, cerebellum, thalami, and inferior frontal lobes); may show no abnormalities on CT, occasionally show zones with intermediate to slightly high attenuation secondary to increased melanin, with or without contrast enhancement. With or without vermian hypoplasia, with or without arachnoid cysts, with or without Dandy-Walker malformation.	Neuroectodermal dysplasia with proliferation of melanocytes in leptomeninges associated with large and/or numerous cutaneous nevi. May change into CNS melanoma.
Myeloma/plasmacytoma	Multiple (myeloma) or single (plasmacytoma) well-circumscribed or poorly defined lesions involving the skull and dura; low to intermediate attenuation, with or without contrast enhancement, with bone destruction.	Myeloma may have variable destructive or infiltrative changes involving the axial and/or appendicular skeleton.
Chordoma Fig. 1.103a–c	Well-circumscribed lobulated lesions, low to intermediate attenuation, with contrast enhancement (usually heterogeneous); locally invasive associated with bone erosion/destruction, encasement of vessels and nerves; skull base–clivus common location, usually in the midline.	Rare, slow-growing, malignant cartilaginous tumors derived from notochordal remnants. Detailed anatomical display of extension of chordomas by CT and MRI is important for planning of surgical approaches.
Chondrosarcoma Fig. 1.104a, b	Lobulated lesions, low to intermediate attenuation, with or without chondroid matrix mineralization, with contrast/enhancement (usually heterogeneous); locally invasive associated with bone erosion/destruction, encasement of vessels and nerves; skull base petro-occipital synchondrosis common location, usually off midline.	Rare, slow-growing tumors. Detailed anatomical display of extension of chondrosarcomas by CT and MRI is important for planning of surgical approaches.
Osteogenic sarcoma	Destructive lesions involving the skull base; low to intermediate attenuation, usually with matrix mineralization/ossification, with contrast enhancement (usually heterogeneous).	Rare lesions involving the skull base and calvarium; more common than chondrosarcomas and Ewing sarcoma; locally invasive; high metastatic potential. Occurs in children as primary tumors and adults (associated with Paget disease, irradiated bone, chronic osteomyelitis, osteoblastoma, giant cell tumor, and fibrous dysplasia).
Ewing sarcoma	Destructive lesions involving the skull base; low to intermediate attenuation; usually lack matrix mineralization, with contrast enhancement (usually heterogeneous).	Rare lesions involving the skull base; usually occur between the ages of 5 and 30 y, males > females; locally invasive; high metastatic potential.
Sinonasal squamous cell carcinoma	Destructive lesions in the nasal cavity, paranasal sinuses, and nasopharynx; with or without intracranial extension via bone destruction or perineural spread; intermediate attenuation; mild contrast enhancement; large lesions (with or without necrosis and/or hemorrhage).	Occurs in adults usually > 55 y, men > women; associated with occupational or other exposure to nickel, chromium, mustard gas, radium, and manufacture of wood products.
Adenoid cystic carcinoma	Destructive lesions in the paranasal sinuses, nasal cavity, and nasopharynx, with or without intracranial extension via bone destruction or perineural spread; intermediate attenuation; variable degrees of contrast enhancement.	Account for 10% of sinonasal tumors; arise from any location within the sinonasal cavities; usually occur in adults older than 30 y.
Arachnoid cyst Fig. 1.105a–d	Well-circumscribed extra-axial lesions with low attenuation equivalent to CSF, no contrast enhancement. Commonly located in the anterior middle cranial fossa > suprasellar/quadrigeminal > frontal convexities > posterior cranial fossa.	Nonneoplastic congenital, developmental, or acquired extra-axial lesions filled with CSF, usually mild mass effect on adjacent brain; supratentorial > infratentorial locations; men > women; with or without related clinical symptoms
Lipoma	Lipomas have CT attenuation similar to subcutaneous fat; typically no contrast enhancement or peripheral edema.	Benign fatty lesions resulting from congenital malformation often located in or near the midline; may contain calcifications and/or traversing blood vessels.
Epidermoid cyst Fig. 1.106a, b	Well-circumscribed spheroid or multilobulated, extra-axial ectodermal inclusion cystic lesions with low to intermediate attenuation, no contrast enhancement, with or without bone erosion/destruction. Often insinuate along CSF pathways; chronic deformation of adjacent neural tissue (brainstem, brain parenchyma). Commonly located in the posterior cranial fossa (cerebellopontine angle cistern) > parasellar/middle cranial fossa.	Nonneoplastic congenital or acquired extra-axial off-midline lesions filled with desquamated cells and keratinaceous debris; usually mild mass effect on adjacent brain; infratentorial > supratentorial locations. Adults: men = women, with or without related clinical symptoms.
Dermoid	Well-circumscribed spheroid or multilobulated extra-axial lesions with variable low, intermediate, and/or high attenuation, contrast enhancement, with or without fluid/fluid or fluid/debris levels. Can cause chemical meningitis if dermoid cyst ruptures into the subarachnoid space. Commonly located: at or near the midline; supratentorial > infratentorial.	Nonneoplastic congenital or acquired ectodermal inclusion cystic lesions filled with lipid material, cholesterol, desquamated cells, and keratinaceous debris; usually mild mass effect on adjacent brain. Adults: men slightly > women; with or without related clinical symptoms.
Fibrous dysplasia Fig. 1.107	Expansile process involving the skull base and calvarium with mixed intermediate attenuation with “ground glass” appearance, heterogeneous contrast enhancement.	Usually seen in adolescents and young adults; can result in narrowing of neuroforamina with cranial nerve compression, facial deformities, mono- and polyostotic forms (with or without endocrine abnormalities, such as with McCune-Albright syndrome, precocious puberty).
Paget disease Fig. 1.108	Expansile sclerotic/lytic process involving the skull with mixed intermediate and high attenuation. Irregular/indistinct borders between marrow and inner margins of the outer and inner tables of the skull.	Usually seen in older adults; can result in narrowing of neuroforamina with cranial nerve compression, basilar impression with or without compression of brainstem.
Inflammatory
Subdural/epidural abscess, empyema	Epidural or subdural collections with low attenuation, thin linear peripheral zones of contrast enhancement.	Often results from complications related to sinusitis (usually frontal), meningitis, otitis media, ventricular shunts, or surgery. Can be associated with venous sinus thrombosis and venous cerebral or cerebellar infarctions, cerebritis, brain abscess; mortality 30%.
Leptomeningeal infection/inflammation Fig. 1.109	Single or multiple nodular-enhancing lesions and/or focal or diffuse abnormal subarachnoid enhancement. Leptomeningeal inflammation often best seen on postcontrast images.	Contrast enhancement in the intracranial subarachnoid space (leptomeninges) usually is associated with significant pathology (inflammation and/or infection vs neoplasm). Inflammation and/or infection of the leptomeninges can result from pyogenic, fungal, or parasitic diseases, as well as tuberculosis. Neurosarcoid results in granulomatous disease in the leptomeninges producing similar patterns of subarachnoid enhancement.
Eosinophilic granuloma Fig. 1.110	Single or multiple circumscribed soft tissue lesions in the marrow of the skull associated with focal bony destruction/erosion with extension extracranially, intracranially, or both. Lesions usually have low to intermediate attenuation, with contrast enhancement, with or without enhancement of the adjacent dura.	Single lesion commonly seen in males > females younger than 20 y; proliferation of histiocytes in medullary cavity with localized destruction of bone with extension in adjacent soft tissues.
		Multiple lesions with syndromes such as Letterer-Siwe disease (lymphadenopathy hepatosplenomegaly), children younger than 2 y; Hand-Schüller-Christian disease (lymphadenopathy, exophthalmos, diabetes insipidus) children 5 to 10 y.
Sarcoidosis	Poorly marginated nodular and/or diffuse contrast enhancement in the leptomeninges; may be associated with intra-axial lesions with contrast enhancement, edema, and localized mass effect.	Multisystem noncaseating granulomatous disease of uncertain cause that can involve the CNS in 5% to 15% of cases. Associated with severe neurologic deficits if untreated.
Other
Vascular AVM Fig. 1.111a, b	Lesions with irregular margins that can be located in the brain parenchyma, (pia, dura, or both locations). AVMs contain multiple tortuous vessels. The venous portions often show contrast enhancement. Usually not associated with mass effect unless there is recent hemorrhage or venous occlusion. CTA can show the arterial, nidus, and venous portions of the AVMs.	Supratentorial AVMs occur more frequently (80%–90%) than infratentorial AVMs (10%–20%). Annual risk of hemorrhage. AVMs can be sporadic, congenital, or associated with a history of trauma.
Dural AVM	Dural AVMs contain multiple tortuous small vessels at the site of a recanalized thrombosed dural venous sinus. Usually not associated with mass effect unless there is recent hemorrhage or venous occlusion.	Dural AVMs are usually acquired lesions resulting from thrombosis or occlusion of an intracranial venous sinus with subsequent recanalization resulting in direct arterial to venous sinus communications. Transverse, sigmoid venous sinuses > cavernous sinuses > straight, superior sagittal sinuses.
Aneurysm Fig. 1.112a, b	Saccular aneurysm: Focal, well-circumscribed zone of soft tissue attenuation, with or without wall calcifications; usually shows contrast enhancement. Fusiform aneurysm: Tubular dilation of the involved artery.	Abnormal fusiform or focal saccular dilation of the artery secondary to acquired/degenerative etiology, polycystic disease, connective tissue disease, atherosclerosis, trauma, infection (mycotic), oncotic, AVM, vasculitis, and drugs. Focal aneurysms, also referred to as saccular aneurysms, typically occur at arterial bifurcations and are multiple in 20% of cases. The chance of rupture of a saccular aneurysm causing subarachnoid hemorrhage is related to the size of the aneurysm. Saccular aneurysms > 2.5 cm in diameter are referred to as giant aneurysms. Fusiform aneurysms are often related to atherosclerosis or collagen vascular disease.
Hemorrhagic Epidural hematoma	Biconvex extra-axial hematoma located between the skull and dura; displaced dura has high attenuation. The CT attenuation and MRI signal of the hematoma depend on its age, size, hematocrit, and oxygen tension; with or without edema (low attenuation on CT and high signal on T2-weighted images) involving the displaced brain parenchyma; with or without subfalcine, uncal herniation. Hyperacute hematoma: CT: Can have high and/or mixed high and intermediate attenuation. MRI: Intermediate signal on T1-weighted images, intermediate to high signal on T2-weighted images. Acute hematoma: CT: Can have high and/or mixed high and intermediate attenuation. MRI: Low to intermediate signal on T1-weighted images, high signal on T2-weighted images. Subacute hematoma: CT: Can have high and/or mixed high and intermediate attenuation. MRI: High signal on T1- and T2-weighted images.	Epidural hematomas usually result from trauma/tearing of an epidural artery or dural venous sinus; epidural hematomas do not cross cranial sutures; with or without skull fracture.
Subdural hematoma	Crescentic extra-axial hematoma located in the potential space between the inner margin of the dura and the outer margin of the arachnoid membrane. The CT attenuation and MRI signal of the hematoma depend on its age, size, hematocrit, and oxygen tension; with or without edema (low attenuation on CT and high signal on T2-weighted images) involving the displaced brain parenchyma; with or without subfalcine, uncal herniation. Hyperacute hematoma: CT: Can have high or mixed high, intermediate, and/or low attenuation. MRI: Intermediate signal on T1-weighted images, intermediate to high signal on T2-weighted images. Acute hematoma: CT: Can have high or mixed high, intermediate, and/or low attenuation. MRI: Low to intermediate signal on T1-weighted images, low signal on T2-weighted images. Subacute hematoma: CT: Can have intermediate attenuation (isodense to brain) and/or low to intermediate attenuation. MRI: High signal on T1- and T2-weighted images. Chronic hematoma: CT: Usually have low attenuation (hypodense to brain). MRI: Variable, often low to intermediate signal on T1-weighted images, high signal on T2-weighted images, with or without enhancement of collection and organizing neomembrane. Mixed MRI signal can result if rebleeding occurs into chronic collection.	Subdural hematomas usually result from trauma/stretching/tearing of cortical veins where they enter the subdural space to drain into dural venous sinuses; subdural hematomas do cross sites of cranial sutures; with or without skull fracture.
Subarachnoid hemorrhage Fig. 1.67a, b , p. 37	CT: Acute subarachnoid hemorrhage typically appears as poorly defined zones with high attenuation in the leptomeninges within the sulci and basal cisterns. Usually becomes isodense or hypodense after 1 week unless there is rebleeding. MRI: May not be seen on T1- or T2-weighted images, although it may have intermediate to slightly high signal on FLAIR images.	Extravasated blood in the subarachnoid space can result from ruptured arterial aneurysms or dural venous sinuses, vascular malformations, hypertensive hemorrhages, trauma, cerebral infarcts, coagulopathy, etc.

**Fig. 1.93a, b Wallerian degeneration.** Atrophy of the left cerebral peduncle (a) is seen on MRI related to prior infarction involving the left basal ganglia (b).

**Fig. 1.94a, b Metastatic tumor, breast carcinoma.** Axial CT image (a) shows a destructive lesion involving the right occipital and temporal bones. The lesion shows contrast enhancement on the axial fat-suppressed, T1-weighted MRI (b), as well as dural involvement.

**Fig. 1.95 Metastatic tumor, leptomeninges.** Postcontrast image shows diffuse tumoral enhancement in the leptomeninges from a pineoblastoma.

**Fig. 1.96 Schwannoma, eighth cranial nerve.** Postcontrast image shows an enhancing lesion in the right cerebellopontine angle cistern that extends into the right internal auditory canal (arrow).

**Fig. 1.97a, b Schwannoma, fifth cranial nerve.** Postcontrast axial CT image (a) shows enhancement of the schwannoma involving the left trigeminal nerve. Similar findings are seen on the postcontrast axial fat-suppressed MRI (arrows) (b).

**Fig. 1.98a, b Meningioma along the petrous bone.** Postcontrast axial CT image (a) shows enhancement of the meningioma along the endocranial surface of the right petrous bone and clivus. Similar findings are seen on the postcontrast axial MRI (b) (arrows).

**Fig. 1.99a, b Meningioma with dense calcifications.** Coronal (a) and axial (b) images show a calcified meningioma adjacent to the right occipital bone.

**Fig. 1.100a–c Paraganglioma/glomus tumor.** Axial CT images (**a,b**) show a soft tissue tumor eroding the right jugular foramen. The tumor has mostly high signal on the axial fat-suppressed, T2-weighted MRI (c), as well as small foci of a low-signal, “salt and pepper” pattern (arrows).

**Fig. 1.101a, b Choroid plexus papilloma.** Axial CT image (a) shows an intraventricular lesion in the fourth ventricle, which shows contrast enhancement on the axial T1-weighted MRI (b).

**Fig. 1.102a, b Choroid plexus carcinoma.** Postcontrast axial CT image (a) shows an enhancing intraventricular lesion in the fourth ventricle, which shows contrast enhancement on the sagittal T1-weighted MRI (b).

**Fig. 1.103a–c Chordoma.** Axial CT image (a) shows the chordoma along the endocranial surface of the clivus causing posterior displacement of the brainstem. The tumor has high signal on the axial fat-suppressed, T2-weighted image (b) and shows heterogeneous contrast enhancement on the axial T1-weighted image (c) (arrows).

**Fig. 1.104a, b Chondrosarcoma.** Axial CT image (a) shows the tumor destroying the clivus and causing posterior displacement of the brainstem. The tumor contains chondroid calcifications and shows heterogeneous contrast enhancement on the axial T1-weighted image (b).

**Fig. 1.105a–d Arachnoid cyst.** (a) The arachnoid cyst with CSF attenuation is located anterior to the brainstem and medial to the right temporal lobe. The cyst has an MRI signal similar to CSF on the axial T1-weighted MRI (b), axial T2-weighted MRI (c), and diffusion-weighted image (d).

**Fig. 1.106a, b Epidermoid.** The lesion is located anterior to the left middle cerebellar peduncle and left cerebellar hemisphere and has low attenuation on the axial CT image (arrow) (a). The epidermoid has high signal from restricted diffusion on the diffusion-weighted image (b).

**Fig. 1.107 Fibrous dysplasia.** Multifocal sites of skull thickening with a “ground glass” appearance are seen in this patient with polyostotic fibrous dysplasia.

**Fig. 1.108 Paget disease.** Axial image shows thickening of the skull with blurring of the margins between the diploic space and the inner and outer tables of the skull.

**Fig. 1.109 Leptomeningeal infection, tubercular meningitis.** Axial postcontrast image shows diffuse abnormal contrast enhancement in the basal meninges and sylvian and interhemispheric fissures.

**Fig. 1.110 Eosinophilic granuloma.** Axial image shows a destructive lesion involving the mastoid portion of the right temporal bone and adjacent right occipital bone.

**Fig. 1.111a, b AVM.** Sagittal CTA image (a) shows an abnormal collection of vessels involving the cerebellum (arrow) that is associated with an intraventricular hemorrhage (b).

**Fig. 1.112a, b Aneurysm.** Postcontrast axial CT image (a) shows the enhancing posterior communicating artery aneurysm indenting the left cerebral peduncle (arrow), as also seen on conventional angiography (b).

**Table 1.6 Cystic, cystlike, and cyst-containing intracranial lesions**
Lesions	CT Findings	Comments
Intra-axial
Astrocytoma	Low-grade astrocytoma: Focal or diffuse mass lesion usually located in the white matter with low to intermediate attenuation, with or without mild contrast enhancement, with or without cysts. Minimal associated mass effect. Fig. 1.113a, b	Often occurs in children and adults (20–40 y). Tumors comprised of well-differentiated astrocytes. Association with neurofibromatosis type 1; 10-y survival; may become malignant.
	Juvenile pilocytic astrocytoma, subtype: Solid/cystic focal lesion with low to intermediate attenuation, usually with prominent contrast enhancement. Lesions located in cerebellum, hypothalamus, adjacent to third or fourth ventricles, and brainstem. Fig. 1.114	Common in children; usually favorable prognosis if totally resected.
	Anaplastic astrocytoma: Often irregularly marginated lesion located in the white matter with low to intermediate attenuation, with or without contrast enhancement, with or without cysts.	Intermediate between low-grade astrocytoma and glioblastoma multiforme; ~2-y survival.
Glioblastoma multiforme Fig. 1.115a, b	Irregularly marginated mass lesion with necrosis or cyst, mixed attenuation, with or without hemorrhage, heterogeneous contrast enhancement, peripheral edema; can cross corpus callosum.	Most common primary CNS tumor; highly malignant neoplasms with necrosis and vascular proliferation; usually seen in patients older than 50 y; extent of lesion underestimated by CT; survival < 1 y.
Oligodendroglioma	Circumscribed lesion with mixed low to intermediate attenuation, clumplike calcifications, heterogeneous contrast enhancement; involves white matter and cerebral cortex, with or without cysts; can cause chronic erosion of inner table of calvarium.	Uncommon slow-growing gliomas with usually mixed histologic patterns (e.g., astrocytomas). Usually seen in adults older than 35 y; 85% supratentorial. If low grade, 75% 5-y survival; higher grade lesions have a worse prognosis.
Central neurocytoma	Circumscribed lesion located at the margin of the lateral ventricle or septum pellucidum with intraventricular protrusion, heterogeneous intermediate attenuation signal, with or without calcifications and/or small cysts; heterogeneous contrast enhancement.	Rare tumors that have neuronal differentiation; imaging appearance similar to intraventricular oligodendrogliomas; occur in young adults; benign slow-growing lesions.
Ganglioglioma, ganglioneuroma, gangliocytoma	Circumscribed tumor, usually supratentorial, often temporal or frontal lobes; low to intermediate attenuation; with or without cysts, with or without contrast enhancement.	Ganglioglioma (contains glial and neuronal elements), ganglioneuroma (contains only ganglion cells). Uncommon tumors seen in patients younger than 30 y; seizure presentation; slow-growing neoplasms. Gangliocytomas contain only neuronal elements, dysplastic brain tissue. Favorable prognosis if completely resected.
Dysembryoplastic neuroepithelial tumor	Circumscribed lesions involving the cerebral cortex and subcortical white matter, low to intermediate attenuation, with or without small cysts, usually no contrast enhancement.	Benign superficial lesions commonly located in the temporal or frontal lobes.
Pleomorphic xanthoastrocytoma	Circumscribed supratentorial lesion involving the cerebral cortex and white matter, low to intermediate attenuation, with or without cyst (s), heterogeneous contrast enhancement, with or without enhancing mural nodule associated with cyst.	Rare type of astrocytoma occurring in young adults and children; associated with seizure history.
Primitive neuroectodermal tumor	Circumscribed or invasive lesions, low to intermediate attenuation signal; variable contrast enhancement, with or without cysts; frequent dissemination into the leptomeninges.	Highly malignant tumors that frequently disseminate along CSF pathways.
Ependymoma Fig. 1.116	Circumscribed lobulated supratentorial lesion, often extra-ventricular, with or without cysts and/or calcifications; low to intermediate attenuation, variable contrast enhancement.	Occurs more commonly in children than adults; one third supratentorial, two thirds infratentorial; 45% 5-y survival
Hemangioblastoma Fig. 1.117	Circumscribed tumors usually located in the cerebellum and/or brainstem; contrast-enhancing nodule with or without cyst, or larger lesion with prominent heterogeneous enhancement with or without vessels within lesion or at the periphery; intermediate attenuation; occasionally lesions have evidence of recent or remote hemorrhage.	Occurs in adolescents, young and middle-aged adults. Lesions are typically multiple in patients with von Hippel-Lindau disease.
Metastases	Circumscribed spheroid lesions in brain can have various intra-axial locations, often at gray-white matter junctions, usually low to intermediate attenuation; with or without hemorrhage, calcifications, cysts; variable contrast enhancement, often low attenuation peripheral to nodular-enhancing lesion representing axonal edema.	Represent ~33% of intracranial tumors, usually from extracranial primary neoplasm in adults older than 40 y.
Pyogenic brain abscess Fig. 1.118a, b	Circumscribed lesion with low attenuation (with or without air-fluid level) surrounded by a thin rim of low to intermediate attenuation that shows ringlike contrast enhancement, as well as a peripheral poorly defined zone of low attenuation representing edema.	Formation of brain abscess occurs 2 weeks after cerebritis with liquefaction and necrosis centrally surrounded by a capsule and peripheral edema. Can be multiple. Complication from meningitis and/or sinusitis, septicemia, trauma, surgery, and cardiac shunt.
Fungal brain abscess Fig. 1.119a, b	Vary depending on organism; lesions occur in meninges and brain parenchyma, solid or cystic lesions with low to intermediate attenuation, nodular or ring contrast enhancement, peripheral low attenuation in adjacent brain tissue.	Occur in immunocompromised or diabetic patients with resultant granulomas in meninges and brain parenchyma. Abscess formation can occur.
Tuberculoma Fig. 1.120	Intra-axial lesions in cerebral hemispheres, basal ganglia, and brainstem (adults), and cerebellum (children). Lesions can have decreased attenuation, central zone of low attenuation with a thin peripheral rim of intermediate attenuation, with solid or rim pattern of contrast enhancement, with or without calcification. Meningeal lesions: Nodular or ring-shaped zones of basilar meningeal enhancement.	Occurs in immunocompromised patients and in inhabitants of developing countries. Caseating intracranial granulomas via hematogenous dissemination; meninges > brain lesions.
Toxoplasmosis	Single or multiple solid and/or ring-shaped lesions located in basal ganglia and/or corticomedullary junctions in cerebral hemispheres, low to intermediate attenuation, nodular or rim pattern of contrast enhancement, with or without peripheral low attenuation (edema).	Most common opportunistic CNS infection in AIDS patients; caused by ingestion of food contaminated with parasites (Toxoplasma gondii).
Cysticercosis	Single or multiple cystic lesions in brain or meninges. Acute/subacute phase: Low to intermediate attenuation, rim with or without nodular pattern of contrast enhancement, with or without peripheral low attenuation (edema). Chronic phase: Calcified granulomas.	Caused by ingestion of ova (Taenia solium) in contaminated food (undercooked pork); involves meninges > brain parenchyma > ventricles.
Hydatid cyst	Echinococcus granulosus: Single or rarely multiple cystic lesions with low attenuation with a thin wall with low to intermediate attenuation; typically no contrast enhancement or peripheral edema unless superinfected; often located in vascular territory of the middle cerebral artery. Echinococcus multilocularis: Cystic (with or without multilocular) and/or solid lesions; central zone of intermediate attenuation surrounded by a slightly thickened rim of low to intermediate attenuation, with contrast enhancement; peripheral zone of low attenuation (edema) and calcifications are common.	Caused by parasites E. granulosus (South America, Middle East, Australia, and New Zealand) and E. multilocularis (North America, Europe, Turkey, and China). CNS involvement in 2% of cases of hydatid infestation.
Demyelinating disease: ADEM, multiple sclerosis	Demyelinating lesions rarely can have a cystlike appearance. Lesions can be located in the cerebral or cerebellar white matter, brainstem, and basal ganglia; Contrast enhancement can be ringlike; usually in acute/early subacute phase of demyelination.	Multiple sclerosis is the most common acquired demyelinating disease. Other demyelinating diseases are acute disseminated encephalomyelitis/immune mediated demyelination after viral infection, toxins, or metabolic disorders.
Radiation necrosis	Focal lesion with or without mass effect or poorly defined zone of low to intermediate attenuation, with or without contrast enhancement involving tissue (gray matter and/or white matter) in field of treatment.	Usually occurs from 4 to 6 months to 10 y after radiation treatment; may be difficult to distinguish from neoplasm. PET and magnetic resonance hydrogen spectroscopy might be helpful for evaluation.
Porencephalic cyst Fig. 1.121	Irregular, relatively well-circumscribed zone with low attenuation similar to CSF, surrounded by poorly defined thin zone of low to intermediate attenuation in the adjacent brain tissue; no contrast enhancement or peripheral edema.	Represent remote sites of brain injury (trauma, infarction, infection, hemorrhage) with evolution into a cystic zone with CSF attenuation surrounded by gliosis in adjacent brain parenchyma. Gliosis (low to intermediate attenuation) allows differentiation from schizencephaly.
Neuroepithelial cyst	Well-circumscribed cysts with low attenuation signal, thin walls; no contrast enhancement or peripheral edema.	Cyst walls have histopathologic features similar to epithelium, neuroepithelial cysts located in choroid plexus > choroidal fissure > ventricles > brain parenchyma.
Extra-axial
Craniopharyngioma Fig. 1.122	Circumscribed lobulated lesions; variable low, intermediate, and/or high attenuation; with or without nodular or rim patterns of contrast enhancement. May contain cysts, lipid components, and calcifications.	Usually histologically benign but locally aggressive lesions arising from squamous epithelial rests along the Rathke cleft; occur in children (10 y) and adults (> 40 y), males = females.
Germinoma Fig. 1.123a, b	Circumscribed tumors with or without disseminated disease; pineal region > suprasellar region > third ventricle/basal ganglia; low to intermediate attenuation; with contrast enhancement of tumor and leptomeninges if disseminated.	Most common type of germ cell tumor; occurs in males > females (10–30 y), usually midline neoplasms.
Teratoma	Circumscribed lesions; pineal region > suprasellar region > third ventricle; variable low to intermediate attenuation; with or without contrast enhancement. May contain calcifications, cysts, as well as fatty components, which can cause chemical meningitis if ruptured.	Second most common type of germ cell tumors; occur in children, males > females; benign or malignant types, composed of derivatives of ectoderm, mesoderm, and/or endoderm.
Pineal cyst Fig. 1.124a, b	Well-circumscribed, extra-axial lesions with low attenuation signal similar to CSF; no central enhancement, thin linear peripheral contrast enhancement; rarely atypical appearance with proteinaceous contents; intermediate, slightly high attenuation.	Common usually incidental nonneoplastic cyst in pineal gland.
Arachnoid cyst Fig. 1.125	Well-circumscribed, extra-axial lesions with low attenuation similar to CSF; no contrast enhancement. Commonly located in the anterior middle cranial fossa > suprasellar/quadrigeminal > frontal convexities > posterior cranial fossa.	Nonneoplastic congenital, developmental, or acquired extra-axial lesions filled with CSF; usually mild mass effect on adjacent brain; supratentorial > infratentorial locations; males > females; with or without related clinical symptoms.
Leptomeningeal cyst	Well-circumscribed, extra-axial lesions with low attenuation similar to CSF, no contrast enhancement. Associated with erosion of the adjacent skull.	Nonneoplastic extra-axial lesions filled with CSF; thought to be secondary to trauma with dural tear/skull fracture; usually mild mass effect on adjacent brain with progressive erosion of adjacent skull; occasionally presents as a scalp lesion; occurs in children > adults.
Colloid cyst	Well-circumscribed spheroid lesions located at the anterior portion of the third ventricle; variable attenuation (low, intermediate, or high), no contrast enhancement.	Common presentation of headaches and intermittent hydrocephalus; removal leads to cure.
Choroid plexus cysts	Low-attenuation cystic structure similar to CSF attenuation within the choroid plexus. On MRI, cysts within the choroid plexus have signal similar to CSF, whereas xanthogranulomatous cysts often have high signal on T2-weighted images and intermediate signal on FLAIR. Xanthogranulomatous cysts have restricted diffusion on diffusion-weighted images as well as apparent diffusion coefficient (ADC) maps.	The choroid plexus can contain incidental simple cysts or xanthogranulomatous cystic lesions.
Epidermoid Fig. 1.126	Well-circumscribed spheroid or multilobulated extra-axial ectodermal inclusion cystic lesions with low to intermediate attenuation that may be similar to CSF; no contrast enhancement. Often insinuate along CSF pathways; chronic deformation of adjacent neural tissue (brainstem, brain parenchyma). Commonly located in the posterior cranial fossa (cerebellopontine angle cistern) > parasellar/middle cranial fossa.	Nonneoplastic congenital or acquired extra-axial off-midline lesions filled with desquamated cells and keratinaceous debris; usually mild mass effect on adjacent brain; infratentorial > supratentorial locations. Adults: men = women; with or without related clinical symptoms.
Dermoid	Well-circumscribed spheroid or multilobulated extra-axial lesions, usually with low attenuation, no contrast enhancement. With or without fluid/fluid or fluid/debris levels. Can cause chemical meningitis if dermoid cyst ruptures into the subarachnoid space. Commonly located at or near the midline; supratentorial > infratentorial.	Congenital or acquired ectodermal inclusion cystic lesions filled with lipid material, cholesterol, desquamated cells, and keratinaceous debris; usually mild mass effect on adjacent brain. Adults: men slightly > women; with or without related clinical symptoms.
Rathke cleft cyst	Well-circumscribed lesion with variable low or intermediate attenuation, no central contrast enhancement, with or without thin peripheral contrast enhancement. Lesion locations: 50% intrasellar, 25% suprasellar, 25% intra- and suprasellar.	Uncommon sella/juxtasellar benign cystic lesion containing fluid with variable amounts of protein, mucopolysaccharide, and/or cholesterol; arise from epithelial rests of the craniopharyngeal duct.
Epidural/subdural empyema Fig. 1.127a, b	Epidural or subdural collections with low attenuation, linear peripheral zones of contrast enhancement.	Often results from complications related to sinusitis (usually frontal), meningitis, otitis media, ventricular shunts, or surgery. Can be associated with venous sinus thrombosis and venous cerebral or cerebellar infarctions, cerebritis, and brain abscess; mortality 30%.
Meningitis Fig. 1.128	Single or multiple nodular-enhancing lesions and/or focal or diffuse abnormal subarachnoid enhancement. Leptomeningeal inflammation often best seen on postcontrast images.	Contrast enhancement in the intracranial subarachnoid space (leptomeninges) usually is associated with significant pathology (inflammation and/or infection vs neoplasm). Inflammation and/or infection of the leptomeninges can result from pyogenic, fungal, or parasitic diseases, as well as tuberculosis. Neurosarcoid results in granulomatous disease in the lepto meninges, producing similar patterns of subarachnoid enhancement.