Arachnoid cyst with acute subdural hemorrhage

Findings

Large left frontal cystic lesion with thin septations and no enhancement. Unclear whether this lesion is intra-axial or extra-axial. No diffusion restriction (image not shown), no surrounding vasogenic edema. Also present is an acute right subdural hematoma caused by the patient's fall.

Differential diagnosis for the cystic lesion:
- Arachnoid cyst
- Ependymal cyst
- Glial cyst


Diagnosis: Arachnoid cyst. Acute subdural hemorrhage.


Key points

Arachnoid cysts are CSF containing cysts which are intra-arachnoid, and do not communicate with the ventricular system.
50-60% occur within the middle cranial fossa.
May arise as a developmental anomaly, or may be acquired as a complication of adhesions.
Small number are associated with neoplasms.
Walls of cyst are formed by splitting of the arachnoid membrane.
Usually asymptomatic. Can have headache or seizures.
The most effective surgical treatment appears to be excision of the outer cyst membrane and cysto peritoneal shunting.

Capillary telangiectasia of the pons

Findings

There is an irregular FLAIR hyperintense focus located along the left anterior aspect of the pons, demonstrating mild lacy contrast enhancement. There is no associated mass effect or restricted diffusion.

Differential diagnosis:
- Developmental venous anomaly
- Cavernous malformation
- Neoplasm
- Inflammation
- Demyelination
- Capillary telangiectasia


Diagnosis: Capillary telangiectasia of the pons


Key points

Capillary telangiectasia
- Represents clusters of dilated capillaries within normal brain
- Usually an incidental finding at imaging
- Represents 15 to 20 percent of brain vascular malformations
- Increased risk for development after brain radiation
- Associated with other vascular malformation, such as cavernous malformation or venous angioma
- Associated with hereditary hemorrhagic telangiectasia

Clinical:
- Usually an incidental finding
- Rarely associated with headache or vertigo
- Found at any age
- No treatment necessary


Imaging

Characteristically found in the pons, but may also be seen in the midbrain, medulla, and elsewhere
Usually small, average 3 cam in diameter
Poorly defined, without mass effect, edema, or restricted diffusion

CT: Usually normal

MRI:
- T1 weighted sequence = usually normal
- T2 weighted sequence = half are normal, half show fine hyperintensity
- Gradient echo = hypointense
- FLAIR = usually normal, but may show foci of hyperintensity
- Diffusion weighted image = usually normal
- Post contrast images = faint lacy or speckled enhancement
- May have associated linear vessels or draining veins if associated with venous angioma

Angiography: Usually occult

Failed back surgery syndrome

Findings

Figure 1: Axial T1 post-contrast weighted image demonstrates a low signal rim-enhancing collection with posterior compression of the thecal sac.
Figure 2: An axial T2 weighted image shows a high-signal epidural collection with posterior compression of the thecal sac.
Figure 3: Sagittal T1 weighted post contrast imaging demonstrates a prior laminectomy with an elongated, peripherally enhancing epidural fluid collection with displacement of the thecal sac anteriorly.
Figure 4: Sagittal T2 weighted image reveals a septated fluid collection with posterior compression of the thecal sac consistent with an epidural abscess.

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Figure 1: Axial T1 weighted image demonstrates a low signal epidural mass in the right neuroforamen with some mass effect on the thecal sac.
Figure 2: Axial T1 post contrast fat suppressed image demonstrates high signal scar or granulation tissue surrounding a low signal right neuroforaminal mass with mass effect on the thecal sac.
Figure 3: One slice below, an axial T1 post contrast fat suppressed image displays the right nerve root surrounded by high signal scar and/or granulation tissue.
Figure 5 and Figure 7: Pre- and post-contrast sagittal T1 image reveals the low signal right neuroforaminal mass to be continuous with the L5-S1 disk with rim enhancement and compression of the thecal sac consistent with a recurrent disk herniation.
Figure 4 and Figure 6: Axial and sagittal T2 weighted images demonstrate a low-signal herniated disk in the right neuroforamen with compression of the thecal sac.


Diagnosis: Failed back surgery syndrome


Failed back surgery syndrome (FBSS) presents with recurrent or persistent low back pain after lumbar spine surgery. Patients may present with weakness and numbness related to lumbar radiculopathy or generalized low back pain. The etiologies of FBSS are vast and include early or late phenomenon. “Early” phenomena include post-operative hemorrhage; infection leading to diskitis, osteomyelitis, meningitis, or epidural abscess; dural tear with pseudomeningocele; sequestered disk fragment; hardware malposition and surgery at the wrong level. These entities demonstrate typical imaging findings depending upon the cause. “Late” etiologies of FBSS include: foraminal or central stenosis (20-60%), instability (14%), recurrent disk herniation (7-12%), epidural fibrosis (5-25%) and arachnoiditis.

Causes of Failed Back Surgery Syndrome:
- Arachnoiditis
- Central or foraminal stenosis
- Epidural Fibrosis
- Infection
- Hematoma
- Surgical trauma to roots
- Insufficient decompression
- Mechanical instability
- Pseudoarthrosis
- Residual or recurrent disk
- Spondylolisthesis
- Surgery at wrong level


Diagnosis of FBSS is made with contrast enhanced MR imaging of the lumbar spine. Canal stenosis is manifest on MR imaging by a “trefoil” appearance of the spinal canal with a thickened ligamentum flavum. Enhancing nerve roots may be present on contrast enhanced imaging. Vertebral body instability can be diagnosed on flexion and extension views on plain radiographs by demonstrating a “dynamic slip” of greater than 3 millimeters. MR findings of instability include antero- or retrolisthesis or loss of disc height with loss of disc signal on T2 weighted images. Epidural fibrosis appears low in signal on T1 weighted images with slightly higher signal than disc on T2 images with diffuse contrast enhancement. This is in contrast to herniated disc material which demonstrates little or thin peripheral enhancement after contrast administration. Post-operative arachnoiditis appears on MR imaging as peripheral or central clumping of nerve roots with variable enhancement.

Because post-operative scarring does not warrant additional surgery, its differentiation from herniated disk is crucial. This is best demonstrated on contrast-enhanced T1 fat saturated weighted images as disc material will demonstrate no or peripheral enhancement while scar tissue will avidly enhance. Additional differentiating features include traction of the dural tube secondary to fibrosis and compression of nerve roots from disk material. MR is 96-100% accurate in detecting epidural fibrosis versus disc material.

Treatment of FBSS is dependent on the etiology. Therapeutic modalities include physiotherapy, epidural steroids, spinal cord stimulators and when warranted, repeat surgery for treatment of recurrent herniation, foraminal stenosis and instability.

Pilocytic astrocytoma

Findings

Large posterior fossa mass with central cystic portion and peripheral thick rind with enhancement and effacement of the 4th ventricle and cerebellar tonsillar herniation. There is secondary mild ventricular enlargement with transependymal edema.

Differential diagnosis:
- Medulloblastoma
- Pilocytic astrocytoma
- Ependymoma


Diagnosis: Pilocytic astrocytoma, atypical


Key points

Juvenile pilocytic astrocytomas are typically benign tumors that arise in the cerebellum, brainstem, hypothalamic region, or optic tracts. The tumor is classified as a WHO grade 1 benign lesion. Their most common site of origin is the cerebellum. It is the most common tumor to occur in the cerebellum. The medulobllastoma is more common in the posterior fossa but it has 4th ventricle origins rather than the cerebellum itself. The tumor generally is found in patients aged 5-14, but can be seen at any age more rarely. There is no sex predilection. The tumors are associated with neurofibromatosis type 1. Common presentations would include ataxia like in this patient, headache, nausea, vomiting or visual disturbances depending on where it is located. Hydrocephalus secondary to mass effect on the fourth ventricle is responsible for the majority of the presentations.

On imaging the tumors are typically well circumscribed with a large cystic component and a mural nodule. The nodule typically enhances. There can be calcification present but only up to 25% of the time. The tumors have a lot of variability in their appearance; they can be entirely solid with or without cystic degeneration. Vasogenic edema is a very uncommon finding and can be used to differentiate this tumor from others in the differential. They are typically hypo attenuating on CT which is helpful in differentiating from a medulloblastoma which is usually hyper attenuating if not at least iso- to the brain secondary to its closely packed cells.

Prognosis for the lesions is quite good. Surgical resection is the first line therapy if the lesion is accessible. Total resection is often possible in the posterior fossa lesions which can yield a 10-year survival rate is as high as 90%. No adjuvant therapy is utilized in that scenario. Even without total resection the 10-year survival rate is still as high as 45%. Radiation therapy had been employed for incomplete resections, but it remains controversial due to risk of brain radiation. Stereotactic radiation is now more commonly used and has shown some promising results. Chemotherapy is reserved for the rare pilocytic astrocytoma that continues to grow post radiation therapy.

Frontoethmoid encephalocele

Findings

Figure 1: Sagittal MR image demonstrates frontal lobe tissue protruding through a defect in the anterior calvarium. A portion of the umbilical cord is seen wrapping around the fetus’s neck.
Figure 2: Axial MR image demonstrates a soft tissue mass protruding between the orbits, with hypertelorism and bilateral hydrocephalus.


Diagnosis: Frontoethmoid encephalocele


A frontoethmoid encephalocele is herniation of intracranial contents through a defect of the skull in the nasofrontal region (1). These are usually detected first on prenatal screening or diagnostic US performed for further evaluation of prenatal screening lab abnormalities, usually elevated maternal serum alpha-fetoprotein levels (2). Sonographic clues include hypertelorism and a facial mass. The best diagnostic clue is visualizing brain parenchyma herniating through an anterior skull defect. Prenatal MR can be used to better delineate the anatomy in a suspected encephalocele, and can better determine size, location, and communication with intracranial structures (1).

Small encephaloceles can be missed on prenatal ultrasound. Other imaging clues include hypertelorism and other associated anomalies which include dysgenesis or absence of the corpus callosum, heterotopia, microcephaly, hydrocephalus, microophthalmos, beaked tectal plate, flattened basiocciput and an interhemispheric lipoma (2). In the postnatal period, they can present as a skin-covered facial or nasal mass (3).

The pathogenesis of an encephalocele is a late neurulation defect during the fourth gestational week. There is a disturbance of separation of the surface ectoderm and neuroectoderm in the midline just following neural fold closure (3). As a result there is failure of the fonticulus frontalis to close with herniation of intracranial parenchyma through persistent embryologic relationships. For unclear reasons, occipital lesions are most common (80%) in North America and Europe (1:35,000 live births) and frontoethmoidal lesions are more common in Southeast Asia (1:5000 lives births) (3).

Prognosis depends on the presence of other associated congenital or developmental brain anomalies. Prognosis is often better with frontoethmoidal lesions than occipital or parietal lesions. An overall mortality of 7-20% has been seen, with a favorable developmental outcome (3). Treatment to prevent infection and further herniation of intracranial contents involves excision of the dysplastic brain tissue with watertight closure of the dura and reconstruction of the skull defect (3). Most of the time, the glial tissue can be resected without causing additional neurological deficits. The exception is in the case of transphenoidal encephaloceles which can contain pituitary gland, hypothalamus or part of the Circle of Willis (3). Hydrocephalus should be treated first (3).

Chiari 2 malformation

Findings

There is enlargement of the lateral ventricles and third ventricle. The fetal Posterior fossa appears small with downward displacement of the cerebellar tonsils. There is discontinuity of the posterior elements beginning at the thoracolumbar junction with myelomeningocele at this level.


Diagnosis: Chiari 2 malformation


Key points

Complex deformity of the calvarium, dura, and hindbrain
Almost always associated with a myelomeningocele
Lacunar skull
Concave clivus and petrous ridge
Small posterior fossa
Fenestrated falx
Cerebellar peg
Medullary kink
Towering cerebellum
The cerebellopontine cistern and the cisterna magna are obliterated
Beaked tectum
Hydrocephalus
Prominent mass intermedia

Carbon monoxide poisoning

Findings

There are fairly symmetric foci of T2 hyper intensity and restricted diffusion in the globus pallidus bilaterally.

Differential Diagnosis:
- Anoxic injury (carbon monoxide)
- Small vessel ischemic disease
- Wilson disease
- Creutzfeldt-Jakob disease
- Leigh's disease


Diagnosis: Anoxic brain injury - Carbon monoxide poisoning


Key points

Changes are typically seen in globus pallidus, but can occur in cerebral white matter (second most common), putamen, caudate, thalamus.

Imaging:
- Hypodense on CT
- T1W can be normal, hypo- or hyperintense (edema or hemorrhage)
- T2W hyperintense
- Diffusion WI restricted diffusion.

Pathologically one sees necrosis in globus pallidus with demyelination of periventricular white matter.
Presents with nonspecific symptoms of variable severity: Nausea / vomiting, headache, confusion, cognitive impairment, seizures, coma, death.
Clinically may have persistent sequelae or resolution of symptoms depending on severity and duration of exposure.
Most common cause of U.S. accidental poisoning
Can confirm diagnosis with carboxyhemoglobin level
Treatment: Hyperbaric O2 for acute cases

Remote cerebellar hemorrhage

Findings

Figure 1, Figure 2, and Figure 3: Three axial brain CT sections reveal subarachnoid hemorrhage in the perimesencephalic, interpeduncular and ambient cisterns. There is also evidence of a right pterional craniotomy. Evidence of a cerebellar hemorrhage is apparent (Figure 2 and Figure 3), remote from the site of aneurysm clipping.
Figure 4: Single axial brain CT on bone windows reveals that the patient is status post a right pterional craniotomy/cranioplasty.


Diagnosis: Remote cerebellar hemorrhage


Remote cerebellar hemorrhage is a self-limited complication of supratentorial craniotomy. Approximately 100 cases have been reported in the literature. Remote cerebellar hemorrhage usually comes to clinical attention post-operatively when brain CT is performed to evaluate altered mental status, new motor deficits or ataxia. The finding may also be incidentally noted on routine postcraniotomy imaging.

Remote cerebellar hemorrhage may occur ipsilateral or contralateral to the craniotomy site. Friedman et al2 studied 43 case of remote cerebellar hemorrhage and concluded that it may accompany supratentorial craniotomies which require access to the ventricular system or basal cisterns. This, in turn, results in loss of cerebrospinal fluid with cerebellar sagging, with occlusion of posterior fossa bridging veins and subsequent hemorrhagic venous infarction.

Other groups3,4 concluded that remote cerebellar hemorrhage was related to the degree of postoperative CSF drainage. This CSF overdrainage results in shifting of the cerebellum caudally with tearing of the superior cerebellar vein and its tributaries, resulting in cerebellar parenchymal hemorrhage. Potential modifiable risk factors associated with remote cerebellar hemorrhage include preoperative aspirin use, perioperative hypertension and male sex.

Management of remote cerebellar hemorrhage is conservative. The hemorrhage is usually self-limiting and does not require intervention. Ventriculostomy may be necessary if hydrocephalus occurs.

Diffuse intrinsic pontine glioma

Additional clinical information: The patient has neurofibromatosis type 1


Findings

Initial CT shows a new central dorsal pontine focus of FLAIR hyperintensity, demonstrating enhancement. One year later, there has been significant increase in the size of a heterogeneously enhancing expansile pontine mass lesion, with extension into the midbrain and along the cerebellar peduncles into the right cerebellar hemisphere.

Differential Diagnosis:
- Pontine Glioma
- Neurofibromatosis Type 1 associated hamartoma or foci of signal intensity
- Brainstem encephalitis
- Acute disseminated encephalomyelitis (ADEM)
- Tuberculoma
- Histiocytosis
- Pontine myelinolysis
- Infarct
- Lymphoma


Diagnosis: Diffuse intrinsic pontine glioma


Key points

Brainstem gliomas
- Represents 12% to 15% of all pediatric brain tumors
- Several types, including diffuse pontine glioma, tectal glioma, focal tegmental mesencephalic
- Histology is usually anaplastic astrocytoma or glioblastoma multiforme
- Does not metastasize outside of the central nervous system


NF1
- Association with tectal and diffuse pontine glioma
- Clinical Presentation:
Presents with headache, ataxia, cranial nerve palsies, hemiparesis
Age of presentation is in children and young adults
No sex predilection
Results in respiratory insufficiency
Treated with chemotherapy and radiation
Poor prognosis in children, with 10 to 30% 5 year survival


Imaging characteristics for diffuse pontine glioma

CT
- Isodense or hypodense, with indistinct margins
- Rare calcification or hemorrhage
- Only 10% will have hydrocephalus
- Variable enhancement

MRI
- Low signal on T1
- High signal on T2
- High signal on FLAIR
- Variable enhancement
- Demonstrates expansion of pons, obstruction of fourth ventricle

Achondroplasia

Findings

Frontal bossing is noted in the calvarium. There is mild narrowing of the foramen magnum. The ventricles and sulci are prominent. There is no mass effect or midline shift. There is no abnormal extra-axial fluid collection. No areas of abnormal attenuation are noted.

Differential diagnosis for frontal bossing and small foramen magnum:
- Achondroplasia
- Thanatophoric dysplasia
- Achondrogenesis
- Camptomelic dysplasia
- Pseudoachondroplasia
- Metatrophic dysplasia
- Hypochondroplasia


Diagnosis: Achondroplasia (skull findings)


Key points

Achondroplasia is a short-stature skeletal dysplasia caused by mutation of fibroblast growth factor receptor-3 gene
Usually not recognized until children > 2 years old
Calvaria enlarged with frontal bossing, megalencephaly
Skull base small with narrow foramen magnum
Narrow jugular foramina may cause hydrocephalus via venous hypertension
Thoraco-lumbar gibbus or kyphosis in infancy
Cervicomedullary decompression surgery in 17%
Short petrous carotid canals
Mastoids under pneumatized
Mid-face hypoplasia, dental crowding
Urgent to treat cranio-cervical junction stenosis to prevent sudden death
Normal lifespan and intelligence

Spinal meningioma

Findings

Sagittal T1 and T2 sequences demonstrate an intradural extramedullary lesion in the midthoracic region which is soft tissue signal on T1 (Figure 1) and soft tissue signal on T2 (Figure 2). Sagittal T2 images demonstrate CSF capping above and below the lesion, which suggests an intradural extramedullary location.
Post contrast images demonstrate homogeneous enhancement of the lesion (Figure 3). A “dural tail” demonstrating the characteristic broad based dural attachment on post gad images is shown.
Incidentally, multiple hemangiomas are demonstrated on sagittal T2 images (Figure 2).


Diagnosis: Spinal meningioma


When evaluating lesions of the spinal cord, it is important to first determine in which space the lesion is located. Lesions may be intramedullary, intradural extramedullary, or extradural.

Meningiomas are the second most common tumor in the intradural extramedullary compartment (nerve sheath tumors most common). Meningiomas account for around 25% all spinal tumors and usually occur in the thoracic spine (80%). 15% of spinal meningiomas occur within the cervical spine. Occasionally, they may be purely extradural, or bridge both the intradural and extradural compartments.

Spinal meningiomas are usually located lateral or dorsolateral in the spinal canal. Since they are thought to arise from arachnoid cluster cells, their location is at the entry zone of nerve roots or the junction of dentate ligaments and dura mater. The spinal cord is usually compressed and displaced away from the lesion.

MR usually demonstrates an intradural extramedullary location. The lesions are usually isointense to the spinal cord on T1 and T2 or alternatively hypointense on T1 and hyperintense on T2. Immediate, homogeneous contrast enhancement is characteristic. Calcification may be seen. Most spinal meningiomas demonstrate broad-based dural attachment, and may show a “dural tail,” as in this case. The subarachnoid space above and below the lesion is widened, described as CSF “capping” of the lesion from below and above. This finding is important in confirming an intradural extramedullary location.

The mainstay of treatment is surgical resection, depending on the extent of the lesion. When complete resection is not possible, post-operative radiotherapy may be performed. Monitoring of symptoms is important following treatment.


Differential diagnosis for each spinal compartment

Mastoiditis with cerebellar abscesses

Additional clinical history: Patient also had ear pain and some drainage from his left ear.


Findings

There are 2 ring-enhancing lesions within the left cerebellum measuring. There is increased signal of the lesions on the DWI images (low values on ADC maps). There is surrounding edema with mass-effect on the pons and brainstem as well as narrowing of the fourth ventricle. There is also thick enhancement of the meninges adjacent to the mastoid bone. There is expansion and enhancement of the mastoid air cells on the left. Other images showed narrowing of the left sigmoid sinus without thrombosis. There is no hydrocephalus.


Diagnosis: Mastoiditis with cerebellar abscesses


Key points

Most brain abscesses are caused by pyogenic bacteria
Most commonly, infectious agents gain access to the CNS by spread from a contiguous focus of infection, such as otitis media, mastoiditis, infection of the paranasal sinuses, or dental infection.
Ring enhancement represents most active area of infection
Diffusion-weighted MR may be useful in differentiating abscess from necrotic tumor. Abscess typically shows as bright areas on DWI with corresponding dark regions of "restricted diffusion" on ADC maps. That is, ADC values should be low in areas that are bright on DWI if the cause is restricted diffusion rather than the phenomenon of T2 shine-through. Necrotic tumors usually have higher ADC values (and corresponding dark areas on DWI).