Mucopolysaccharidoses (MPS) / Hurler disease

Findings

Figure 1: T1-weighted image showing dilated perivascular spaces.
Figure 2: Abnormal T2-signal in surrounding white matter. T2-weighted image showing dilated perivascular spaces.


Diagnosis: Mucopolysaccharidoses (MPS) / Hurler disease


Mucopolysaccharidoses (MPS) are inherited disorders of metabolism which are characterized by the inability to break down glycosaminoglycan (GAG) because of an enzyme deficiency. This results in an accumulation of toxic intracellular substrate. There are multiple MPS, classified from MPS 1-9, depending upon the specific enzyme deficiency. The prototype is MPS 1H, which is Hurler disease. This is caused by alpha-L-Iduronidase deficiency.

On noncontrast CT there is macrocrania. The dilated perivascular spaces are rarely visible on CT. There is progressive hydrocephalus and atrophy. On contrast enhanced CT there is often enhancing pannus associated with the ligaments and dura at the craniocervical junction.

A classic diagnostic imaging finding on MRI is dilated perivascular spaces (PVS) or Virchow-Robin spaces. This will appear as dark on T1WI and bright on T2WI. The dilated PVS are usually under 5 mm, but can be larger, and range from one to many. The most common locations are the corpus callosum and peritrigonal white matter, but can occur anywhere. On T2WI, there is often increased signal of the white matter surrounding the dilated PVS, which is a result of gliosis, edema, demyelination or dysmyelination. On FLAIR, there may be increased signal surrounding the PVS.

Hemangioblastoma

Findings

There is a right parasagittal lesion along the medial aspect of the cerebellum. The cystic mass has pronounced mass-effect on the dorsal brainstem and tectum. Extending from the cyst wall along one of the septations is an enhancing nodule.

Differential diagnosis:
- Hemangioblastoma (given patient age, the most likely diagnosis)
- Medulloblastoma
- Pilocytic astrocytoma


Diagnosis: Hemangioblastoma


Key points

The hemangioblastoma (HB) is a vascular neoplasm of unknown etiologycular. Cerebellar hemangioblastoma is the most common primary brain neoplasm involving the infratentorial space in adults. This benign tumor is readily curable by surgery. More than 85% of hemangioblastomas occur in the cerebellum, with the remainder occurring in the spinal cord, medulla, and cerebrum in a 4:2:1 ratio. Approximately 10% of posterior fossae masses are hemangioblastomas. Men are more commonly affected than females, and patients are usually young adults. The common symptoms are headache, nausea, vomiting, ataxia, and vertigo. In 40% of patients, polycythemia is present secondary to increased erythropoietin produced by the tumor (more common in solid tumors). A spinal hemangioblastoma may present with subarachnoid hemorrhage.

The classic findings of an HB are that of a cystic mass with a solid mural nodule (60% of cases), which is highly vascular and has serpentine signal voids of feeding vessels. However, 40% of HBs are solid. Less commonly, these tumors may be purely cystic. Overall, HB is a rare tumor representing 1-2.5 % of primary CNS neoplasms; 10-20% of all cases are associated with with von-Hippel-Lindau syndrome; converesly, 45% of patients with VHL develop HBs.

Treatment: Treatment frequently requires removal of the mural nodule only, since the cyst is not truly neoplastic. Preoperative embolization aids in resection of the highly vascular tumors. Prognosis is very good with 5-year a survival rate of more than 85%.


Radiology

Angiography: Vascular nodule with intense, prolonged stain; +/- avascular cyst.
CT: Low-density cyst with strongly enhancing mural nodule that abuts a pial surface (75%)
MRI: Cyst slightly hyperintense to CSF on T1WI; hyperintense to brain on T2WI; mural nodule variable but typically enhances strongly

Acute subdural hematoma

Findings

There is acute subdural hematoma along the tentorium. This extends along the posterior interhemispheric fissure. The ventricles are prominent out of proportion to the sulci raising the possibility of obstructive hydrocephalus. The fourth ventricle is normal in size. No definite tectal mass is appreciated.

Differential diagnosis: "Bright tentorium"
- Subdural hematoma
- Epidural hematoma
- Aneurysmal bleed
- Metastatic disease to the cerebellum with local bleeding
- Isodense primary CNS tumor (meningioma) with focal bleeding

Other subdural fluid collection
- Hygroma (clear CSF, no encapsulating membranes)
- Effusion (xanthochromic fluid from extravasation of plasma from outer membrane; 20% evolve into chronic SDH)
- Empyema (peripheral enhancement, restricted diffusion centrally)

Epidural Hematoma
- Biconvex extra-axial collection
- Often associated with fracture
- May cross dural attachments, limited by sutures
- Pachymeningopathies (thickened dura)

Chronic meningitis (may be indistinguishable)
- Post-surgical (shunt, etc)
- Intracranial hypotension ("slumping" midbrain, tonsillar herniation)
- Sarcoid (nodular, "lumpy-bumpy")

Tumor
- Meningioma, lymphoma, leukemia, metastases
- Dural based, enhancing mass
- ± Skull involved


Diagnosis: Acute subdural hematoma


Key points

Acute (± 6 hrs-3 days) hemorrhagic collection in subdural space
Diagnostic clue: Crescent-shaped, homogenously hyperdense on CT, extra-axial collection that spreads diffusely over affected hemisphere
May cross sutures, not dural attachments
May extend along falx & tentorium
Compresses & displaces underlying brain
Recurrent, mixed-age hemorrhage in a child raises suspicion of non accidental trauma!
CT density & MR signal intensity vary with age & organization of hemorrhage
Protocol advice: Use wide window settings (150-200 HU) to identify small SDH

Etiology
- Trauma most common
Stretching & tearing of bridging cortical veins as they cross subdural space to drain into dural sinus
Both nonimpact as well as direct injury
Trauma may be minor, particularly in elderly

- Less common etiologies include
Dissection of intraparenchymal hematoma into subarachnoid, then subdural space
Aneurysm rupture
Vascular malformations: Dural AVF, AVM, cavernoma
Coagulopathy

Predisposing factors
- Atrophy
- Shunting (leads to increased traction on superior cortical veins)
- Arachnoid cyst (middle fossa most common site)

Epidemiology: SDH found in 10-20% imaged & 30% autopsy cases following craniocerebral trauma
Associated abnormalities: > 70% of aSDH have other significant associated traumatic lesions

Persistent Trigeminal Artery (PTA)

Findings

In Figure 1, an artery can be seen branching from the cavernous portion of the left internal carotid artery and joining the basilar artery. Notice the absence of this vessel on the right.


Diagnosis: Persistent Trigeminal Artery (PTA)


In the 3-5 mm human embryo, approximately 29 days after ovulation, four important arterial anastamoses join the dorsal aorta (the future internal carotid artery) to the bilateral longitudinal neural arteries (the future basilar artery). They are the trigeminal, otic, hypoglossal and proatlantal intersegmental arteries. The largest of these is the trigeminal artery. These arteries persist about a week and regress as the posterior communicating and vertebral arteries develop. For reasons that are not fully understood, these arteries sometimes fail to regress.

The most common persistent carotid-vertebrobasilar anastamotic artery is the trigeminal artery. The incidence has been reported to be about 0.2%, but if undiagnosed and unreported cases are taken into account, this number may approach 1%. There are two main classifications of a persistent trigeminal artery based on its anatomic position; lateral and medial. The lateral type leaves the cavernous sinus to course with the trigeminal root on the lateral side of the sella turcica in a groove of the posterior petrosal process and joins the basilar artery between the origin of the anterior inferior cerebellar artery and superior cerebellar artery. The medial type penetrates the sella turcica to run in its own groove and perforates the dura near the clivus to join the basilar artery.

A persistent trigeminal artery is usually an incidental finding, but has been reported to present with several clinical manifestations. Patients with a persistent trigeminal artery are at an increased risk of developing aneurysms. These aneurysms can be located either at their origin from the internal carotid artery or at their connection with the basilar artery. Depending on the artery’s anatomic location relative to the trigeminal and abducens nerves, patients can present with trigeminal neuralgia or sixth nerve palsies. Patients can present with vertigo and ataxia from embolization of a carotid atherosclerotic plaque through a persistent trigeminal artery into the posterior circulation. Patients can present with the same symptoms with a carotid occlusion which can cause a vascular steal phenomenon from the basilar artery to the carotid system through a persistent trigeminal artery. Patients with complications from a persistent trigeminal artery can be treated with endovascular or surgical interventions.

Right cerebellar infarct demonstrating luxury perfusion

Findings

CT shows right cerebellar hemispheric hypoattenuation with edema, mass effect, and effacement of the 4th ventricle. Angiogram shows contrast blush in the right inferior cerebellar hemisphere with an early draining vein ("luxury perfusion"). Anterior and inferior displacement of the right PICA branch. No evidence of vertebral dissection or vascular malformation.


Diagnosis: Right cerebellar infarct demonstrating luxury perfusion


Key points

Luxury perfusion is a term used to describe increased circulation through an area of infarcted brain.
Thought to be due do vasodilation secondary to lowered oxygen tension and decrease tissue pH. (Loss of normal CBF autoregulation).
Angiographically seen as capillary blush and early filling of local veins.
The blush may simulate a tumor
Luxury perfusion can be seen in minutes to hours after infarction, usually resolves in 3-5 days. Never seen after 2 weeks.

Repeat selected MR image





Findings

Figure 1: Initial CT of the head showed an intraparenchymal bleed in the left frontal subcortical region.
Subsequent MRI showed the bleed to be predominantly isointense on T1-WI (Figure 2) and heterogeneously bright on T2-WI (Figure 3), suggestive of hyperacute to acute stage. Mild perilesional edema is seen with no abnormal adjacent flow voids. Generalized volume loss is also noted. Gradient echo images (Figure 4 and Figure 5) show multiple, patchy areas of hemorrhage in the bilateral superficial, subcortical white matter appearing as areas of susceptibility.
Follow-up MRI shows the intraparenchymal bleed as high-signal on T1-WI (Figure 6) and hyperintense on T2-WI (Figure 7) suggestive of late-subacute nature of bleed.


Diagnosis: Cerebral amyloid disease (angiopathy)


Cerebral amyloid disease is a localized form of amyloidosis characterized by extracellular deposition of ß-amyloid in the brain, and it is not associated with systemic amyloidosis. It is found at autopsy in 33% of 60–70 year olds and the prevalence increases to 75% of people older than 90 years. Cerebral amyloid deposition occurs in three morphologic varieties, with cerebral amyloid angiopathy (CAA) being the most common with deposition of ß-amyloid protein in the media and adventitia of small and medium-sized vessels of the cerebral cortex, subcortex, and leptomeninges. Amyloidoma and diffuse encephalopathic white matter involvement are rare.

Many cases of CAA are asymptomatic. When symptomatic, typical presentations include acute intracranial hemorrhage, symptoms resembling a transient ischemic attack (TIA), or dementia. However, these symptoms are not specific for CAA and are often not readily associated with CAA. With continued aging of the population, CAA will become even more prevalent, making correct characterization of imaging findings important.

The deposition of ß-amyloid in the vessel wall is associated with fibrinoid necrosis, focal vessel wall fragmentation, and microaneurysms, which all predispose the patient to repeated episodes of blood vessel leakage or frank hemorrhage. Luminal narrowing may occur at sites of fibrinoid necrosis, which can lead to ischemic change. Histologically, ß-amyloid deposits stained with Congo red show classic yellow-green birefringence under polarized light.

Nonenhanced head CT is the preferred initial imaging modality as it provides crucial information regarding the characteristics of the intracranial hemorrhage, including size, location, shape, and extension to the extra axial spaces. MRI is best suited for identification of small or chronic cortical hemorrhages and ischemic sequalae of this disease, exclusion of other causes of acute cortical-subcortical hemorrhage, and assessment of disease progression. GRE is currently the most sensitive MR imaging sequence for detection of the chronic cortical-subcortical microhemorrhages. Local magnetic field inhomogeneity related to the presence of hemosiderin causes a marked loss of signal on T2*-weighted GRE imaging.

CAA-related ICH represents only 2% of all ICH but is an important cause of hemorrhage in normotensive elderly patients without trauma, representing 38% to 74% of ICH cases in the elderly. CAA-related ICH exhibits a distinctive cortical-subcortical distribution that generally spares the deep white matter, basal ganglia, and brainstem. Angiography does not play a role in the evaluation of CAA.

CAA should be considered in the broad differential diagnosis of leukoencephalopathy, especially if associated with cortical-subcortical hemorrhage(s) or progressive dementia. In CAA, atrophy is most likely the result of chronic small vessel ischemia related to ß-amyloid deposition and is usually seen in association with leukoencephalopathy.

There is no current treatment to halt or reverse ß-amyloid deposition. Patients with CAA have an increased risk of bleeding while taking warfarin, even when the level of anticoagulation is in the therapeutic range. The risk-benefit ratio of anticoagulation and thrombolytic therapy in CAA patients should be carefully considered on an individual basis.

Olivopontocerebellar degeneration

Findings

Figure 1, Figure 2 and Figure 3: Axial T2 images exhibit reduced brainstem and cerebellar volume, and enlargement of the 4th ventricle and perimesencephalic cistern. Note the normal appearance of the supratentorial brain (Figure 3).
Figure 4 and Figure 5: Sagittal T1 images demonstrate reduced brainstem and cerebellar volume, flattening of the pons, a narrow middle cerebellar peduncle, and enlargement of the 4th ventricle.


Diagnosis: Olivopontocerebellar degeneration


Olivopontocerebellar degeneration (OPCD), once known as Dejerine-Thomas syndrome, is a neurodegenerative disorder caused by progressive infratentorial neuronal loss. The clinical presentation is variable; however, certain features predominate: parkinsonism, pyramidal dysfunction, autonomic dysfunction, and cerebellar ataxia. There is significant overlap with other neurodegenerative disorders including Shy-Drager syndrome, progressive supranuclear palsy, and striatonigral degeneration. These disorders sometimes being referred to as the “Parkinson Plus” syndromes.

Differentiation from Parkinson disease can be extremely difficult with clinical findings alone. It is also important to exclude other causes of progressive neurological decline, such as malignancy, multiple sclerosis, or cerebrovascular disease. Accurate diagnosis is crucial for purposes of patient management, prognosis, and genetic counseling.

The imaging findings of OPCD include pronounced degenerative changes throughout the brainstem and cerebellum as evidenced by flattening of the pons, reduced volume of the medullary olives and middle cerebellar peduncle, and enlargement of CSF spaces including the fourth ventricle and perimesencephalic cistern. This atrophy should be disproportionate to that found throughout the remainder of the brain. Occasionally, demyelination of the transverse pontine fibers may result in a cruciform shaped region of hyperintensity on T2WI, irreverently termed the “Hot Cross Bun” sign.

Evaluation of the middle cerebellar peduncle width is helpful in confirming the diagnosis of OPCD. A measurement of less than 8mm in the sagittal plane has been shown to be both highly sensitive and specific for the disease. Not necessary for diagnosis, but of potential academic interest- these patients will generally demonstrate reduced FDG metabolism on PET and depressed NAA/Cr ratios on MR spectroscopy in the affected areas.