3 Lesions Involving the Meninges and Skull

10.1055/b-0034-75775

3 Lesions Involving the Meninges and Skull

Meyers\, Steven P.

The cranial and spinal meninges represent three concentric contiguous membranes (dura mater, arachnoid, and pia mater) surrounding the central nervous system (CNS). The outer intracranial meningeal layer is the dura mater (pachymeninx). The outermost layer of the dura mater is a richly vascularized layer with elongated fibroblasts and large intercellular spaces that contain arteries and veins; this layer represents the periosteum of the inner table of the calvaria. The arteries and veins here form impressions on the inner table of the skull. The outer layer of the dura mater terminates at the foramen magnum. An inner layer of the dura arises from the meninx and consists of epithelial cells. This inner layer of the dura mater is contiguous with the spinal dura mater. The layers of the cranial dura separate at sites where there are large venous sinuses. Reflections of dura form the falx cerebri and tentorium cerebelli, which provide support of the normal positions of the cerebrum and cerebellum.

The arachnoid and pia mater comprise the leptomeninges. The arachnoid membrane is immediately adjacent to the inner surface of the dura. A potential space exists between the dura and the arachnoid, referred to as the subdural space. The arachnoid is thinner over the convexities than at the base of the skull. Deep to the arachnoid membrane is the subarachnoid space, which contains cerebrospinal fluid (CSF). The inner boundary of the subarachnoid space is the cranial pia mater. The cranial pia mater is a thin layer adjacent to the surface of the brain extending along the sulci. The cranial pia mater contains elastic fibers internally and collagenous fibers peripherally. Thin connective tissue strands and cellular septa extend across the arachnoid membrane to the pia except at the base of the brain, where the arachnoid membrane and pia are widely separated. These regions are referred to as the basal subarachnoid cisterns. The spinal pia mater is thicker and more adherent to the nervous tissue than the cranial pia.

The meninges (dura, arachnoid, and pia) form the extra-axial compartments of the CNS. The epidural space exists when the dura is detached from the inner table, usually from trauma/fracture and injury to a meningeal artery/epidural hematoma or occasionally from neoplasms involving the skull. The subdural space forms when a pathologic process is present, such as a subdural hematoma from trauma/skull fracture and injury of large veins, inflammatory/infectious disease, or neoplasm. Unlike the epi- and subdural compartment, the subarachnoid space exists without the presence of a pathologic process. The presence of extravascular blood in the subarachnoid space usually is associated with a ruptured intracranial aneurysm, vascular malformation, or trauma. Contrast enhancement of the dura can occur as a result of various causes, including neoplasms (primary and metastatic); inflammation/infection; and benign dural fibrosis secondary to intracranial surgery, transient hypotension (secondary to lumbar puncture), or evolving subdural hematoma. The dural enhancement follows the inner contour of the calvaria without extension into the sulci.

Contrast enhancement in the intracranial subarachnoid space (leptomeninges) is nearly always 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. Complications of infectious meningitis include cerebritis, intra-axial abscess, ventriculitis, hydrocephalus, and venous sinus thrombosis/venous cerebral infarction. Neurosarcoid results in granulomatous disease in the leptomeninges producing similar patterns of subarachnoid enhancement. Disseminated or meta-static disease involving the leptomeninges can result from CNS tumors or primary tumors outside the CNS. Lymphoma and leukemia can also result in a similar pattern of leptomeningeal enhancement. Rarely, transient leptomeningeal enhancement can occur from chemical irritation resulting from subarachnoid blood.

Skull

The skull is comprised of two major components, the neuro-cranium and viscerocranium. The viscerocranium represents the facial bony structures. The neurocranium is the portion that encloses the brain and includes the skull base (chondrocranium, endochondral bone formation) and calvarium (membranous bone formation). Chondrocranial bones of the skull base include the sphenoid bone, most of the occipital bone, petrous bones, and ethmoid bone. Sites where the chondrocranial bones of the skull base fuse are referred to as synchondroses. The calvarium originates from ossification centers derived from membranous bone. Growth of the calvarium is directly dependent on growth of the immediately subadjacent dura. The orientation of the dural fibers is related to the position of five chondrocranial structures of the skull base (both petrous crests, crista galli, and both lesser sphenoid wings). Calvarial bones include frontal bones (two), parietal bones (two), a small portion of the occipital bone, and squamous portions of temporal bones (two).

Membranous borders between calvarial bones are referred to as sutures. The coronal suture is located between the frontal and parietal bones, the sagittal suture between the parietal bones, the lambdoid suture between the parietal and occipital bones, and the metopic suture between the frontal bones. The metopic suture normally closes approximately 7 months after birth. Junction regions where three or more calvarial bones meet are referred to as fontanelles. The largest is the anterior fontanelle, which is located between the frontal and parietal bones. The other fontanelles are considerably smaller and include the posterior, posterolateral (mastoid), and anterolateral (sphenoid) fontanelles. The size of the calvarial portion of the skull is dependent on growth of the intra cranial contents (brain and ventricles). Patients with micro-cephalic brains have small-sized calvarial vaults, and those with enlarged brains (e.g., neoplasms, Alexander and Canavan diseases, and/or hydrocephalus) have enlarged calvaria. Premature closure of one or more sutures (craniosynostosis) results in various deformities of the calvaria depending on which suture is involved.

Growth of the chondrocranial bones of the skull base are less dependent on brain growth as is the calvarium. Disorders of skull base development are usually on a genetic basis (e.g., achondroplasia). Anomalies in brain formation can also affect development of the skull base. Examples include Chiari II malformations and cephaloceles. Chiari II malformations result in a small posterior cranial fossa and an enlarged foramen magnum. Cephaloceles are congenital defects in the skull through which there is herniation of the meninges and CSF or the meninges, CSF/ventricles, and brain tissue. The occipital cephalocele is the most common type in the Western hemisphere, and the frontoethmoidal type is most common in Southeast Asia. Other cephalocele locations are the parietal and sphenoid bones.

Cephaloceles can also result from trauma and surgery.

Pathologic processes involving the skull can result by direct extension from adjacent anatomical structures (sinusitis resulting in osteomyelitis, intracranial neoplasm or inflammation eventually involving the skull, etc.), hematogenous seeding of infection or neoplasm into the diploic compartment, or systemic disorders (myeloma, thalassemia, sickle cell disease, hyperparathyroidism, renal osteodystrophy, etc.). Primary pathologic conditions involving the skull include craniosynostosis, Paget disease, trauma/fracture, neoplasm, infection/inflammation, nonmalignant lesions (epidermoid, hemangioma, etc.), and dermal sinus and vascular abnormalities (e.g., sinus pericranii).

**Table 3.1 Abnormalities involving the meninges**
Lesions	CT Findings	Comments
Developmental
Cephaloceles (meningoceles or meningoencephaloceles) Fig. 3.1a, b	Defect in skull through which there is herniation of meninges and CSF (meningocele) or meninges, CSF/ventricles, and brain tissue (meningoencephaloceles).	Congenital malformation involving lack of separation of neuroectoderm from surface ectoderm with resultant localized failure of bone formation. Occipital location most common in Western hemisphere, frontoethmoidal location most common site in Southeast Asians. Other sites include parietal and sphenoid bones. Cephaloceles can also result from trauma or surgery.
Neurofibromatosis type 1 (NF1) osseous dysplasia/meningeal ectasia Fig. 3.2	NF1 associated with focal ectasia of intracranial dura, widening of internal auditory canals from dural ectasia, and dural and temporal lobe protrusion into orbit through a bony defect (bony hypoplasia of the greater sphenoid wing).	Autosomal dominant disorder (1/2500 births) representing the most common type of neurocutaneous syndromes, associated with neoplasms of the central and peripheral nervous systems and skin. Also associated with meningeal and skull dysplasias.
Neoplastic
Meningioma Fig. 3.3a, b	Extra-axial dural-based lesions, well circumscribed; supratentorial > infratentorial, parasagittal > convexity > sphenoid ridge > parasellar > posterior fossa > optic nerve sheath > intraventricular; intermediate attenuation; usually prominent contrast enhancement, with or without calcifications, adjacent skull hyperostosis.	Most common extra-axial tumor, usually benign; typically occurs in adults older than age 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 Fig. 3.4a, b	Extra-axial mass lesions, often well circumscribed; intermediate attenuation; prominent contrast enhancement (may resemble meningiomas); with or without associated erosive bone changes.	Rare neoplasms in young adults (males > females) sometimes referred to as angioblastic meningioma or meningeal hemangiopericytoma; arise from vascular cells/pericytes; frequency of metastases > meningiomas.
Metastatic tumor Fig. 3.5a, b	Single or multiple well-circumscribed or poorly defined lesions involving the skull, dura, lepto meninges, brain, 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. Primary tumors can be within or outside the CNS. Metastatic disease can result from hematogenous dissemination, direct extension from bone lesions, or via the CSF pathways.
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.
Vascular
Arterial aneurysm Fig. 3.6	Saccular aneurysm: Focal, well-circumscribed zone of low to intermediate attenuation; variable mixed attenuation if thrombosed; with or without calcifications. CTA shows contrast enhancement of the nonthrombosed aneurysm. Giant aneurysm: Focal, well-circumscribed structure with layers of low, intermediate, and high attenuation secondary to layers of thrombus of different ages, as well as a contrast-enhancing patent lumen if present. Fusiform aneurysm: Elongated and ectatic arteries; variable low to intermediate attenuation. Dissecting aneurysms: The involved arterial wall is thickened and has intermediate attenuation. CTA shows the narrowing or occlusion of the vessel lumen.	Abnormal fusiform or focal dilation of artery secondary to acquired/degenerative etiology, polycystic disease, connective tissue disease, atherosclerosis, trauma, infection (mycotic), oncotic, arteriovenous malformation (AVM), vasculitis, and drugs. Focal aneurysms are also referred to as saccular aneurysms, which typically occur at arterial bifurcations and are multiple in 20% of patients. Saccular aneurysms > 2.5 cm in diameter are referred to as giant aneurysms. Fusiform aneurysms are often related to atherosclerosis or collagen vascular disease (e.g., Marfan and Ehlers-Danlos syndromes). Dissecting aneurysms: hemorrhage occurs in the arterial wall from incidental or significant trauma.
AVM Fig. 3.7a, b	Lesions with irregular margins that can be located in the brain parenchyma (pia, dura, or both locations). AVMs contain multiple tubular vessels from patent arteries, as well as thrombosed vessels, areas of hemorrhage in various phases, calcifications, and gliosis. The venous portions often show contrast enhancement. CTA can provide additional detailed information about the nidus, feeding arteries, and draining veins, as well as the presence of associated aneurysms. Usually not associated with mass effect unless there is recent hemorrhage or venous occlusion.	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. Multiple AVMs can be seen in syndromes: Rendu Osler-Weber (AVMs in the brain and lungs and mucosal capillary telangiectasias) and Wyburn-Mason (AVMs in the brain and retina with cutaneous nevi).
Dural AVM	Dural AVMs contain multiple tortuous tubular vessels. The venous portions often show contrast enhancement. CTA can show patent portions of the vascular malformation and areas of venous sinus occlusion or recanalization. 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 sinus > straight, superior sagittal sinuses.
Moyamoya Fig. 3.8a, b	Multiple tortuous tubular vessels can be seen in the basal ganglia and thalami secondary to dilated collateral arteries, with enhancement of these arteries. Often with contrast enhancement of the leptomeninges related to pial collateral vessels. Decreased or absent contrast enhancement of the supraclinoid portions of the internal carotid arteries and proximal middle and anterior cerebral arteries. CTA shows stenosis and occlusion of the distal internal carotid arteries with collateral arteries (lenticulostriate, thalamoperforate, and leptomeningeal) best seen after contrast administration enabling detection of slow blood flow.	Progressive occlusive disease of the intracranial portions of the internal carotid arteries with resultant numerous dilated collateral arteries arising from the lenticulostriate and thalamoperforate arteries, as well as other parenchymal, leptomeningeal, and transdural arterial anastomoses. Term translated as “puffof smoke,” referring to the angiographic appearance of the collateral arteries (lenticulostriate, thalamoperforate). Usually nonspecific etiology, but can be associated with neurofibromatosis, radiation angiopathy, atherosclerosis, and sickle cell disease; usually children > adults in Asia.
Sturge-Weber syndrome Fig. 3.9a–c	Prominent localized unilateral leptomeningeal contrast enhancement usually in parietal and/or occipital regions in children; with or without gyral enhancement; mild localized atrophic changes in the brain adjacent to the pial angioma; with or without prominent medullary and/or subependymal veins; with or without ipsilateral prominence of choroid plexus. Gyral calcifications > 2 y; progressive cerebral atrophy in region of pial angioma.	Also known as encephalotrigeminal angiomatosis, neurocutaneous syndrome associated with ipsilateral “port wine” cutaneous lesion and seizures; results from persistence of primitive leptomeningeal venous drainage (pial angioma) and developmental lack of normal cortical veins, producing chronic venous congestion and ischemia.
Hemorrhagic (trauma, vascular malformation, or aneurysm)
Epidural hematoma	Biconvex extra-axial hematoma located between the skull and dura; displaced dura has high attenuation. The CT attenuation of the hematoma depends on its age, size, hematocrit, and oxygen tension. With or without edema (low attenuation on CT) involving the displaced brain parenchyma; with or without subfalcine, uncal herniation. Hyperacute hematomas: CT: Can have high and/or mixed high and intermediate attenuation. Acute hematoma: CT: Can have high and/or mixed high and intermediate attenuation. Fig. 3.10 Subacute hematoma: CT: Can have high and/or mixed high and intermediate attenuation.	Epidural hematomas usually result from trauma/tearing of an epidural artery (often the middle meningeal artery) or dural venous sinus; epidural hematomas do not cross cranial sutures; with or without skull fracture.
Hemorrhagic lesion
Subdural hematoma	Crescentic extra-axial hematoma located in the potential space between the inner margin of the dura and outer margin of the arachnoid membrane. The CT attenuation of the hematoma depends on its age, size, hematocrit, and oxygen tension. With or without edema (low attenuation on CT) 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. Acute hematoma: CT: Can have high or mixed high, intermediate, and/or low attenuation. Fig. 3.11 Subacute hematoma: CT: Can have intermediate attenuation (isodense to brain) and/or low to intermediate attenuation.	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. 3.12	Chronic hematoma: CT: Acute subarachnoid hemorrhage typically appears as poorly defined zones with high attenuation in the leptomeninges within the sulci and basal cisterns. Usually become isodense or hypodense after 1 week unless there is rebleeding.	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.
Inflammatory
Epidural/subdural abscess/empyema Fig. 3.13 Fig. 3.14	Epidural or subdural collections with low attenuation and 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, and brain abscess; mortality 30%.
Leptomeningeal infection/inflammation Fig. 3.15 Fig. 3.16a, b	Single or multiple nodular contrast-enhancing lesions and/or focal or diffuse abnormal subarachnoid contrast 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.
Postsurgical pseudomeningocele Fig. 3.17	CSF-filled collection contiguous with the subarachnoid space with or without herniated brain tissue protruding through a surgical bony defect.	Usually not clinically significant unless it becomes large or infected.

**Fig. 3.1a, b Cephalocele.** Axial computed tomography (CT) image (a) shows a frontal meningoencephalocele that traverses a skull defect, as seen on the coronal CT image (b).

**Fig. 3.2 Dural ectasia/osseous dysplasia.** Axial CT image in a patient with neurofibromatosis type 1 shows the absence of the right greater sphenoid wing with protrusion of the meninges and right temporal lobe into the right orbit.

**Fig. 3.3a, b Meningioma.** Sagittal (a) and coronal (b) postcontrast images show an enhancing meningioma along the olfactory groove.

**Fig. 3.4a, b Hemangiopericytoma.** Axial postcontrast CT image (a) and coronal postcontrast T1-weighted magnetic resonance imaging (MRI) (b) shows an enhancing extra-axial tumor.

**Fig. 3.5a, b Metastatic tumor.** Axial postcontrast images show an enhancing disseminated subarachnoid tumor from a pineoblastoma.

**Fig. 3.6 Aneurysm.** Axial computed tomography angiography (CTA) image shows an enhancing aneurysm at the lateral M1 portion of the left middle cerebral artery (arrow).

**Fig. 3.7a, b Arteriovenous malformation (AVM).** Axial (a) and coronal (b) postcontrast images show a collection of tortuous enhancing blood vessels in the upper posterior left parietal lobe representing an AVM.

**Fig. 3.8a, b Moyamoya.** Axial (a) and coronal (b) CTA images show severe stenosis of the upper right internal carotid artery with collateral leptomeningeal and lenticulostriate vessels around the M1 segment of the right middle cerebral artery (arrows).

**Fig. 3.9a–c Sturge-Weber syndrome.** Axial CT images (**a,b**) show gyriform calcifications and an enhancing pial angioma in the left occipital region, the latter of which is also seen (arrow) on a postcontrast axial T1-weighted MRI (c).

**Fig. 3.10 Epidural hematoma.** Acute epidural hematoma with high attenuation is seen in the right frontal region with compression of the right frontal lobe.

**Fig. 3.11 Subdural hematoma.** Subdural hematoma on the left is seen associated with subfalcine herniation rightward.

**Fig. 3.12 Subarachnoid hemorrhage.** Axial image shows diffuse high attenuation in the basal cisterns and subarachnoid space from acute hemorrhage.

**Fig. 3.13 Epidural empyema.** Postcontrast axial image shows an epidural empyema in the left frontal region.

**Fig. 3.14 Subdural empyema.** Postcontrast axial image shows a subdural empyema on the left (arrows) and low attenuation of the anterior right frontal lobe from cerebritis.

**Fig. 3.15 Leptomeningeal infection/tuberculosis.** Axial postcontrast image shows diffuse abnormal contrast enhancement of the basal meninges and subarachnoid space, as well as several ring-enhancing lesions.

**Fig. 3.16a, b Leptomeningeal inflammation/sarcoid.** Axial postcontrast images show abnormal enhancement involving the brain and falx from sarcoid granulomas.

**Fig. 3.17 Postsurgical pseudomeningoencephalocele.** Axial image shows a right craniectomy defect through which the brain and meninges have herniated.

**Table 3.2 Lesions involving the skull**
Tumor/Tumorlike Lesion	CT Findings	Comments
Malignant neoplasms
Metastatic tumor Fig. 3.18	Single or multiple well-circumscribed or poorly defined lesions involving the skull, dura, leptomeninges, brain, and/or choroid plexus; often show contrast enhancement, with or without bone destruction, with or without compression of neural tissue or vessels. Leptomeningeal tumor often best seen on postcontrast images.	May have variable destructive or infiltrative changes involving single or multiple sites of involvement. Primary tumors are usually from outside CNS.
Myeloma/plasmacytoma	Multiple (myeloma) or single (plasmacytoma) well-circumscribed or poorly defined lesions involving the skull and dura; low to intermediate attenuation; usually show contrast enhancement, with bone destruction.	Malignant plasma cell tumor; may have variable destructive or infiltrative changes involving the axial and/or appendicular skeleton.
Lymphoma	Single or multiple well-circumscribed or poorly defined lesions involving the skull, dura, and/or leptomeninges; low to intermediate attenuation; may show 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.
Leukemia	Single or multiple well-circumscribed or poorly defined lesions involving the skull, dura, and/or leptomeninges; low to intermediate attenuation; may show 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.
Chordoma Fig. 3.19a–c	Well-circumscribed, lobulated lesions; low to intermediate attenuation; usually shows 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 tumors at the skull base; detailed anatomical display of extension of chordomas by CT and MRI is important for planning of surgical approaches.
Chondrosarcoma Fig. 3.20a–c	Lobulated lesions, low to intermediate attenuation, with or without matrix mineralization; can show contrast enhancement (often heterogeneous); locally invasive associated with bone erosion/destruction, encasement of vessels and nerves, skull base/petrous/occipital synchondrosis common location, usually off midline.	Rare, slow-growing, malignant cartilaginous tumors; detailed anatomical display of extension of chondrosarcomas by CT and MRI is important for planning of surgical approaches.
Osteogenic sarcoma Fig. 3.21a, b	Destructive lesions involving the skull base and calvarium; low to intermediate attenuation, usually with matrix mineralization/ossification; often shows 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 Fig. 3.22	Destructive lesions involving the skull base and calvarium; low to intermediate attenuation; can show contrast enhancement (usually heterogeneous).	Malignant bone tumors that usually occur between the ages of 5 and 30, males > females; rare lesions involving the skull base; locally invasive, high meta-static potential.
Sinonasal/nasopharyngeal carcinoma Fig. 3.23a–c	Destructive lesions in the nasal cavity, paranasal sinuses, nasopharynx; with or without intracranial extension via bone destruction or perineural spread; intermediate attenuation, can show contrast enhancement; large lesions (with or without necrosis and/or hemorrhage).	Occurs in adults usually older than age 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, 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 in any location within sinonasal cavities; usually occurs in adults older than age 30 y.
Esthesioneuroblastoma	Locally destructive lesions with low to intermediate attenuation; usually shows contrast enhancement. Location: superior nasal cavity, ethmoid air cells with occasional extension into the other paranasal sinuses, orbits, anterior cranial fossa, cavernous sinuses.	Malignant tumors also referred to as olfactory neuroblastoma arise from olfactory epithelium in the superior nasal cavity. Occur in adolescents and adults, men = women.
Rhabdomyosarcoma	Lesions have low to intermediate attenuation with circumscribed and/or poorly defined margins. Areas of hemorrhage may be present. Lesions may have heterogeneous attenuation. Zones of edema may occur in the adjacent soft tissues. Tumors can be associated with destructive changes of adjacent bone; show variable degrees and patterns of contrast enhancement.	Malignant mesenchymal tumors with rhabdomyoblastic differentiation that occur primarily in soft tissue and only very rarely in bone. Occur most frequently in children.
Hemangiopericytoma	Extra-axial mass lesions, often well circumscribed; intermediate attenuation; usually show prominent contrast enhancement (may resemble meningiomas); with or without associated erosive bone changes.	Rare neoplasms in young adults (males > females) sometimes referred to as angioblastic meningioma or meningeal hemangiopericytoma; arise from vascular cells/pericytes; frequency of metastases > meningiomas.
Meningioma Fig. 3.24a, b	Extra-axial dural-based lesions, well-circumscribed; supratentorial > infratentorial; parasagittal > convexity > sphenoid ridge > parasellar > posterior fossa > optic nerve sheath > intraventricular; intermediate attenuation; typically show prominent contrast enhancement, with or without calcifications, with or without hyperostosis and/or invasion of adjacent skull.	Most common extra-axial tumors; usually benign neoplasms; typically occur in adults (> 40 y), women > men; multiple meningiomas seen with neurofibromatosis type II; can result in compression of adjacent brain parenchyma, encasement of arteries, and compression of dural venous sinuses; rarely invasive/malignant types.
Hemangioma Fig. 3.25	Circumscribed or poorly marginated structures (< 4 cm in diameter) in marrow of skull (often frontal bone) with intermediate attenuation; prominent bone trabeculae may be seen; typically show contrast enhancement, with or without widening of diploic compartment.	Benign skull lesions, adults (> 30 y).
Ossifying hemangioma Fig. 3.26a–c	Zone with low to intermediate attenuation; usually show prominent contrast enhancement.	Benign lesions within the temporal bone that involve the facial nerve and on CT are usually radiolucent, containing bone spicules. Lesions can be associated with slowly progressive or recurrent facial paralysis.
Osteoid osteoma Fig. 3.27	Intraosseous circumscribed radiolucent lesion < 1.5 cm in diameter surrounded by bone sclerosis. Lesions often have low to intermediate attenuation centrally; often show contrast enhancement, surrounded by a peripheral rim of increased attenuation from associated bone sclerosis.	Benign osseous lesion containing a nidus of vascularized osteoid trabeculae surrounded by osteoblastic sclerosis that rarely occurs in the skull. Usually occurs between the ages of 5 and 25 y, males > females. Focal pain and tenderness associated with lesion that is often worse at night, relieved with aspirin.
Osteoblastoma	Expansile radiolucent lesion often > 1.5 cm surrounded by bone sclerosis. Lesions can show contrast enhancement.	Rare benign bone neoplasm (2% of bone tumors) usually occurs between the ages of 6 and 30 y; rarely involves the skull.
Enchondroma Fig. 3.28a–c	Lobulated intramedullary lesion that usually has low to intermediate attenuation and contains areas of chondroid matrix mineralization and fibrous strands. Lesions can show contrast enhancement.	Benign intramedullary lesions composed of hyaline cartilage; represent <10% of benign bone tumors. Enchondromas can be solitary (88%) or multiple (12%).
Chondroblastoma	Tumors often have fine lobular margins and typically have low to intermediate attenuation containing chondroid matrix mineralization (50%); contrast enhancement may be seen. Cortical destruction is uncommon.	Benign cartilaginous tumors with chondroblast-like cells and areas of chondroid matrix formation that rarely occur in the craniofacial bones. The squamous portion of the temporal bone is the most common location.
Pituitary adenoma Fig. 3.29a, b	Macroadenomas (> 10 mm): Commonly have intermediate attenuation, with or without necrosis, with or without cyst, with or without hemorrhage; usually show contrast enhancement, extension into suprasellar cistern with waist at diaphragma sella, with or without extension into cavernous sinus; occasionally invades skull base.	Common benign, slow-growing tumors representing <50% of sellar/parasellar neoplasms in adults. Can be associated with endocrine abnormalities related to oversecretion of hormones (prolactin > nonsecretory type > growth hormone > adrenocorticotropic hormone [ACTH]). Prolactinomas: women > men; growth hormone tumors: men = women.
Paraganglioma/glomus jugulare Fig. 3.30a–c	Ovoid or fusiform lesions with low to intermediate attenuation. Lesions can show contrast enhancement; often erode adjacent bone.	Benign encapsulated neuroendocrine tumors that arise from neural crest cells associated with autonomic ganglia (paraganglia) throughout the body. Lesions, also referred to as chemodectomas, are named according to location (glomus jugulare, tympanicum, vagale).
Endolymphatic sac cystadenoma	Extra-axial retrolabyrinthine lesions involving the posterior petrous bone extending into the cerebellopontine angle cistern. Lesions can have low to intermediate attenuation and can show contrast enhancement. May contain blood products.	Rare solid and/or cystic benign or malignant papillary adenomatous tumors arising from the endolymphatic sac in children and adults. Tumors are slow growing and rarely metastasize; may be sporadic or associated with von Hippel-Lindau disease.
Other lesions
Osteoma Fig. 3.31a–c	Well-circumscribed lesions involving the skull with high attenuation; typically show no contrast enhancement.	Benign proliferation of bone located in the skull or paranasal sinuses (frontal > ethmoid > maxillary > sphenoid).
Epidermoid Fig. 3.32a–c	Well-circumscribed, spheroid ectodermal inclusion cystic lesions in the skull associated with chronic bone erosion; low to intermediate attenuation; no contrast enhancement.	Nonneoplastic lesions filled with desquamated cells and keratinaceous debris involving the skull.
Dermoid	Well-circumscribed, spheroid lesions in the skull associated with chronic bone erosion; usually with low attenuation, no contrast enhancement, with or without fluid–fluid or fluid–debris levels.	Nonneoplastic ectodermal inclusion cystic lesions involving the skull filled with lipid material, cholesterol, desquamated cells, and keratinaceous debris.
Aneurysmal bone cyst Fig. 3.33a, b	Circumscribed extradural vertebral lesion usually involving the posterior elements with or without involvement of the vertebral body; with variable low, intermediate, or high attenuation; with or without lobulations, with or without one or multiple fluid/fluid levels.	Expansile blood/debris-filled lesions that may be primary or occur secondary to other bone lesions, such as giant cell tumor, fibrous dysplasia, and chondroblastoma. Most occur in patients older than 30 y. These lesions rarely involve the skull.
Giant cell reparative granuloma	Lesions are radiolucent and can have heterogeneous low to intermediate attenuation.	Giant cell reparative granulomas are also referred to as solid aneurysmal bone cysts (ABCs). Histologic appearance resembles brown tumors.
Arachnoid cyst	Well-circumscribed, extra-axial lesions with low attenuation similar to CSF; no contrast enhancement. Chronic erosive changes can be seen at the adjacent skull.	Nonneoplastic acquired, developmental, or congenital extra-axial cysts filled with CSF. Cysts can be small or large, asymptomatic or symptomatic.
Inflammatory lesions
Pyogenic osteomyelitis Fig. 3.34a, b	Zones of abnormal decreased attenuation, focal sites of bone destruction, with or without complications including subgaleal empyema, epidural empyema, subdural empyema, meningitis, cerebritis, intra-axial abscess, and venous sinus thrombosis.	Osteomyelitis of the skull can result from surgery, trauma, hematogenous dissemination from another source of infection, or direct extension of infection from an adjacent site, such as the paranasal sinuses.
Eosinophilic granuloma Fig. 3.35	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; can show contrast enhancement, with or without enhancement of the adjacent dura.	Single lesions commonly seen in males > females younger than age 20 y; proliferation of histiocytes in medullary cavity with localized destruction of bone with extension in adjacent soft tissues.
		Multiple lesions associated with Letterer-Siwe disease (lymphadenopathy hepatospleno megaly), children younger than 2 y; Hand-Schüller- Christian disease (lymphadenopathy, exophthalmos, diabetes insipidus), children ages 5 to 10 y.
Sarcoidosis	Sarcoid lesions within marrow can be multiple or solitary, with or without bone expansion and/or erosions or areas of destruction of the inner and/or outer tables with extension intracranially or into the extracranial soft tissues. Lesions can have circumscribed and/or indistinct margins and usually have low to intermediate attenuation signal; can show variable degrees of contrast enhancement.	Chronic systemic granulomatous disease of unknown etiology in which noncaseating granulomas occur in various tissues and organs, including bone.
Paranasal sinus mucocele Fig. 3.36a, b	Circumscribed expansile lesion within a paranasal sinus that has variable low, intermediate, and/or high attenuation depending on contents of mucus, inspissated mucus, and protein concentration.	Lesions occurring from chronic obstruction of a paranasal sinus ostium that results in outward expansion of the osseous margins from remodeling secondary to increased pressure from accumulated secretions from the sinus mucosa. Mucoceles occur most commonly in the frontal sinuses, followed by the ethmoid, maxillary, and sphenoid sinuses.
Cholesterol granuloma Fig. 3.37a, b	Circumscribed lesion measuring between 2 and 4 cm in the marrow of the petrous bone often associated with mild bone expansion. Lesions usually have low attenuation.	Lesions seen in young and middle-aged adults and occur when there is obstruction of mucosal-lined air cells in the petrous bone. Multiple cycles of hemorrhage and granulomatous reaction result in accumulation of cyst contents with cholesterol granules, chronic inflammatory cells, red blood cells, hemosiderin, fibrous tissue, and debris.
Acquired
Aneurysm	Focal, circumscribed lesion with low to intermediate and/or high attenuation. CTA shows contrast enhancement of nonthrombosed portions of lumens of aneurysms.	Abnormal dilation of artery secondary to acquired/degenerative cause, connective tissue disease, atherosclerosis, trauma, infection (mycotic), AVM, drugs, and vasculitis.
Postsurgical pseudomeningocele Fig. 3.38	CSF-filled collection contiguous with the subarachnoid space protruding through a surgical bony defect. Gliotic brain tissue may also accompany the dural protrusion.	Usually not clinically significant unless it becomes large or infected.
Paget disease Fig. 3.39	Expansile sclerotic/lytic process involving the skull with mixed intermediate to high attenuation. Irregular/indistinct borders are seen between marrow and inner margins of the outer and inner tables of the skull.	Usually seen in older adult;, can result in narrowing of neuroforamina with cranial nerve compression, basilar impression, with or without compression of brainstem.
Fibrous dysplasia Fig. 3.40	Expansile process involving the skull with mixed intermediate and high attenuation, often in a “ground glass” appearance; can show 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).
Hematopoietic disorders	Enlargement of the diploic space with red marrow hyperplasia and thinning of the inner and outer tables.	Thickening of diploic space related to erythroid hyperplasia from anemia related to sickle cell disease, thalassemia major, and hereditary spherocytosis. Similar findings of red marrow expansion can be seen with polycythemia rubra.
Osteopetrosis Fig. 3.41a, b	Findings include generalized bone sclerosis, hyper-ostosis resulting in thickening of the skull, as well as narrowing of the foramina and optic canals.	Heterogeneous group of bone disorders with defective resorption of primary spongiosa and mineralized cartilage from osteoclast dysfunction. Results in failure of conversion of immature woven bone into strong lamellar bone and pathologic fractures. In the severe autosomal recessive form, medullary crowding from immature sclerotic bone can result in anemia, thrombocytopenia, and immune dysfunction leading to death.
Hyperostosis frontalis Fig. 3.42	Expansion of the medullary portion of the upper frontal bone extending intracranially with well-defined cortical margin of the inner table of the skull.	Benign bilateral bone overgrowth involving the inner table of the frontal bone; most often seen in elderly women.
Trauma
Cephalohematoma Fig. 3.43a, b	Hematoma located beneath periosteum of outer table; does not cross suture lines; with or without skull fracture; with or without subdural hematoma.	Results from birth trauma (complication of forceps delivery); associated with 1% of births.
Fracture Fig. 3.44	Nondisplaced/nondepressed skull fractures: With or without subgaleal hematoma, with or without epidural hematoma, with or without subdural hematoma, with or without subarachnoid hemorrhage. Depressed skull fracture: Angulation and internal displacement of fractured skull, with or without subgaleal hematoma, with or without epidural hematoma, with or without subdural hematoma, with or without subarachnoid hemorrhage.	Traumatic fractures of the skull can involve the calvarium or skull base; significant complications that can result include epidural hematoma, subdural hematoma, subarachnoid hemorrhage, CSF leakage/rhinorrhea, and otorrhea.
Congenital abnormalities
Cephaloceles (meningoceles or meningoencephaloceles) Fig. 3.45a, b	Defect in skull through which there is herniation of meninges and CSF (meningocele) or meninges, CSF/ventricles, and brain tissue (meningoencephaloceles).	Congenital malformation involving lack of separation of neuroectoderm from surface ectoderm with resultant localized failure of bone formation. Occipital location most common in Western hemisphere; frontoethmoidal location most common site in Southeast Asians. Other sites are parietal and sphenoid bones. Cephaloceles can also result from trauma or surgery.
Chiari II malformation/lückenschädel skull Fig. 3.46a, b	Multifocal scalloping at the inner table of the skull.	Also referred to as lacunar skull or craniolacunae, dysplasia of membranous skull/calvarium in Chiari II with multifocal thinning of the inner table from nonossified fibrous bone from abnormal collagen development and ossification.
Craniosynostosis Fig. 3.47a, b Fig. 3.48a–c Fig. 3.49a, b	Premature closure; metopic suture results in trigonocephaly (wedge-shaped skull), sagittal suture results in scaphocephaly (long, narrow-shaped skull), coronal or lambdoid suture results in oxycephaly, and unilateral closure of coronal or lambdoid sutures result in plagiocephaly.	Premature closure of the cranial sutures results in abnormal skull shape. Can be primary from abnormal development or secondary from external forces of intrauterine compression, lack of brain growth, and/or teratogens; 15% are associated with other anomalies; 80% involve one suture. Closure of multiple sutures is often associated with genetic etiology.
Achondroplasia Fig. 3.50	The calvarium/skull vault is enlarged in association with a small skull base and narrow foramen magnum. Cervicomedullary myelopathy and/or hydrocephalus can result from a narrowed foramen magnum.	Autosomal dominant mutation (fibroblast growth factor gene 3; 1/10 000 births) in which the mutated gene impairs endochondral bone formation, resulting in decreased longitudinal lengthening of long bones.
Basiocciput hypoplasia Fig. 3.51	Hypoplasia of the lower clivus results in primary basilar invagination.	The lower clivus is a portion of the occipital bone (basiocciput) that is composed of four fused sclerotomes. Failure of formation of one or more of these sclerotomes results in a shortened clivus and primary basilar invagination (dens extending > 5 mm above the Chamberlain line).
Condylus tertius Fig. 3.52	Ossicle seen between the lower portion of a shortened basiocciput and the dens/atlas.	Condylus tertius or third occipital condyle results from lack of fusion of the lowermost fourth sclerotome (proatlas) with the adjacent portions of the clivus. This third occipital condyle can form a pseudojoint with the anterior arch of C1 and/or dens and can be associated with decreased range of movement.
Atlanto-occipital assimilation	Often seen as fusion of the occipital condyle with one or both lateral masses of C1.	Occurs from failure of segmentation of the occipital condyle and the C1 vertebra.
Neurofibromatosis type 1 (NF1) Fig. 3.53a, b	NF1 associated with focal ectasia of intracranial dura, widening of internal auditory canals from dural ectasia, dural and temporal lobe protrusion into orbit through bony defect (bony hypoplasia of greater sphenoid wing), bone malformation, or erosion from plexiform neurofibromas.	Autosomal dominant disorder (1/2500 births) representing the most common type of neurocutaneous syndromes; associated with neoplasms of central and peripheral nervous systems and skin. Also associated with meningeal and skull dysplasias.