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).