Neurocysticercosis

Findings

Figure 1: CT scan demonstrates a right-sided parietal lobe intraaxial cystic structure with a central “dot” representing a scolex.
Figure 2: CT scan reveals multiple cysts at the level of the brainstem and right temporal lobe. These cysts show wall enchancement on postcontrast imaging with surrounding edema. These findings, combined with the patient’s acute symptoms, are consistent with the diagnosis of cysts in the colloidal vesicular stage.
Figure 3, Figure 4, and Figure 5: T1 , FLAIR and T1 postcontrast images, respectively, show cysts with surrounding edema in the region of the brainstem that enhance with contrast.


Diagnosis: Neurocysticercosis


Neurocysticercosis is an intracranial parasitic infection caused by the pork tapeworm, Taenia solium. The parasite is endemic in parts of Mexico, Central and South America, Asia, Africa, and Eastern Europe. The parasite is acquired by ingestion of insufficiently cooked pork containing the encysted larvae or through fecal-oral route. The larva develops into adult tapeworms within the human intestinal tract. The oncospheres (active embryo) released from the ova of the adult tapeworm by gastric digestion burrow through the intestinal tract to the bloodstream.

The most common presenting symptom is seizure; however, the interval between the date of infection and symptoms varies from less than one year to 30 years. Symptoms do not present until larval death. Once the larva dies, there is an acute inflammatory response that may cause meningitis. Disease presentation varies depending on the location of the cysts. Cysts in the subarachnoid space can produce basal meningitis, hydrocephalus, and mass lesions. However, cysts in the suprasellar cistern, cerebellopontine angle, and sylvian cistern may cause cerebral arteritis with subsequent infarction of the middle cerebral or posterior cerebral distribution.

There are four stages of cyst formation that parallel the imaging findings:
1) Vesicular stage: The larvae are alive and the cyst contains clear fluid. There is minimal edema and the cyst has a thin capsule. The cyst is isointense to CSF on MR, and an eccentric scolex can be identified as a mural nodule.
2 & 3) Colloidal vesicular and granular nodular stage: The fluid within the cyst becomes turbid as the larvae dies and leaks into the surrounding tissue, causing a strong inflammatory response. Imaging studies show ring enhancement and capsular thickening. The cyst shrinks in the granular nodular stage to approximately 33% of its original size and shows nodular enhancement. Cysts are usually isodense or hyperintense to CSF on T1-weighted imaging and T2-weighted imaging or FLAIR.
4) Nodular calcified stage: During this stage, CT is more specific than MR. There will be low-density cysts with focal calcifications.

Completion of the four stages ranges from two to 10 years, with an average of five years. Serologic testing of serum or CSF for specific antibodies, or ELISA, aid in determining a diagnosis. Travel history is often essential in reaching a diagnosis.

Chiari I malformation

Findings

Figure 1 and Figure 2: Sagittal T1 and Sagittal T2 images showing tonsillar herniation, as well as the presence of syringomyelia at the level of the cervical cord.
Figure 3 and Figure 4: Axial imaging demonstrates the presence of a cervical syrinx on T1 and T2.


Diagnosis: Chiari I malformation


Chiari malformations are a spectrum of anomalies associated with a reduction of posterior cranial fossa volumes and CSF while conserving overall brain volume. Chiari I malformations refer to a greater than 5 mm herniation of the cerebellar tonsils down through the foramen magnum. The cerebellar vermis and ventricular system are typically unaffected, and the fourth ventricle is usually normal. In its pure form, the tonsils fall to the C1-C2 level, with the brain stem seen in normal position.

Hydromyelia (a dilatation of the central canal within the spinal cord) or syringomyelia (paracentral canal dilatation) is seen in 20% to 70% of Chiari I individuals. In symptomatic patients with herniation greater than 5 mm, syringomyelia has been seen in approximately 50% of the cases. Dilatation occurs, as there is backup of CSF and increased pressure within the affected canal. In addition, 20% of Chiari I patients have hydrocephalus.

Chiari I is also associated with numerous skeletal abnormalities. Unlike Chiari II malformations, Chiari I is not associated with myelomeningocele.

A genetic basis for Chiari I has been suggested by its association with achondroplasia, Hadju-Cheney syndrome (a very rare connective tissue and bone disorder affecting skull base, mandible, and fingers), and Klippel-Feil syndrome (C2-C3 fusion), along with reports of familial pattern of occurrence and concordance in monozygotic twins.

Patients typically present in the second or third decade of life with suboccipital headaches, retro-orbital pressure or pain, clumsiness, dizziness, vertigo, tinnitus, muscle weakness, and lower cranial nerve symptoms. Women are more frequently affected than men.

X-ray will show the associated skeletal anomalies, such as skull base invagination, scoliosis, kyphosis, cervical ribs, and many other skeletal anomalies. Axial images with CT may demonstrate an obliterated cisterna magna, tonsillar ectopia, and a normal fourth ventricle. CT may be useful in patients who have contraindications to MRI. MRI is the study of choice, as tonsillar position and configuration are easily identified along with other associated findings, such as syringomyelia. Most findings are best viewed in the sagittal plane.

Giant paraclinoid ICA aneurysm

Findings

Noncontrast CT: Peripheral calcifications. High density lumen (Figure 1) representing nonthombosed blood in the aneurysm lumen.
T1-weighted MRI (Figure 2), T2-weighted MRI (Figure 3): Hemorrhage of varying ages in aneurysm wall including T1 bright, T2 bright crescent-shaped hyperacute periluminal blood in wall (Figure 2 and Figure 3) representing methemoglobin. Pulsation artifact due to blood flow in patent lumen (Figure 2 and Figure 3).


Diagnosis: Giant paraclinoid ICA aneurysm


Giant cerebral aneurysms, defined as cerebral aneurysms greater than 2.5 cm in size, typically occur in the fifth to seventh decade with slight female preponderance. These aneurysms commonly present with symptoms related to subarachnoid hemorrhage – severe headache, nausea, vomiting, and loss of consciousness – or progressive neurologic dysfunction due to mass effect. Patients may also present with signs and symptoms caused by cerebral ischemia secondary to dislodged intramural thrombus.

Partially thrombosed giant aneurysms have a characteristic MRI appearance due to its dual component nature (thrombosed portion with layering clot, and patent portion with flowing blood). Typically, they appear as well-circumscribed mass lesions with mixed signal intensities and varying ages of clot in the thrombosed portion of the aneurysm. The patent portion will demonstrate evidence of flow including signal void, enhancement, and pulsation artifact.

Giant aneurysms are classified as saccular, fusiform, or serpentine giant types:
1) Saccular aneurysms are believed to arise from smaller saccular aneurysms. Proposed mechanisms include turbulent flow, which induces endothelial damage from turbulent flow that induces recurrent scarring, and mural thrombus formation. Another theory is that there are recurrent hemorrhages in the aneurysm wall, causing expansion.

2) Fusiform aneurysms develop from artherosclerotic degeneration of the arterial wall and involve longer segments of intracranial arteries.

3) Serpentine aneurysms are a type of fusiform aneurysm with irregular, tortuous lumen. Development is not well understood.

Treatment options are varied and are dependent on each individual case, including direct clipping of the neck (particularly for narrow-necked saccular aneurysms), surgical ligation, endovascular treatment, and surgical bypass

Sturge-Weber syndrome (SWS)

Findings

Plain films (Figure 1 and Figure 2) show “tram track” calcification in the right frontal region. The gyral or subcortical calcification is better seen in the CT image (Figure 3).
Axial T1 image (Figure 4) demonstrates volume loss in the right frontal area with thickened diploic space in this region. Sagittal SE image (Figure 5) shows multiple round signal voids, which are dilated deep medullary veins.
Postcontrast images (Figure 7 and Figure 8) show leptomeningeal enhancement, suggestive of increased venous collaterals and prominence of the right transmantle (transcerebral) veins (Figure 6). Also note the enlarged ipsilateral right choroid plexus (Figure 7).
GRE (Figure 7) shows “blooming” in the right frontal area corresponding to the area of calcification seen on CT.
MRV (Figure 9) findings demonstrate a hypoplastic right transverse sinus as well as a very small right-sided jugular vein.


Diagnosis: Sturge-Weber syndrome (SWS)


SWS, also known as encephalotrigeminal angiomatosis or meningiofacial angiomatosis, is a rare neurocutaneous syndrome that includes a facial port wine stain and associated leptomeningeal angiomatosis. The pial angiomatosis may be bilateral in 20% of cases.

It is generally considered nonhereditary. Embryologically, the abnormality most likely develops at gestational weeks four to eight. It is hypothesized that impaired venous outflow, caused by loss of normal connections between cortical veins and dural and calvarial circulation, results in persistent, primitive vascular plexus. This results in poor venous drainage from the cerebral cortex and progressive cortical damage.

Seizures often begin in the first year of life. It is the presenting feature in 80% of patients and may be generalized or partial. Hemiparesis may occur in up to 30% of cases resulting from hemiatrophy of brain. Developmental delay is common.

The port wine stain (nevus flammeus) usually occurs in the distribution of first and second division of trigeminal nerve. The choroid of eye may be involved with patients developing glaucoma.

The impaired venous drainage results in progressive ischemia of underlying brain and, eventually, progressive cortical atrophy and calcification. The cortical calcifications are rarely identified at birth. The most common area involved is the parieto-occipital region. Skull radiographs may show the typical “tram track” calcifications in apposing gyri. CT may also show enlargement of adjacent diploic space, hyperpneumatizaton of ipsilateral sinuses, and mastoid air cells.

MRI may show signs of ischemia and gliosis in early stages, but parenchymal atrophy over time. Gadolinium-enhanced MRI is highly sensitive to meningeal enhancement. Calcifications are better detected with gradient echo techniques. Enlargement of the ipsilateral choroid plexus may be secondary to hyperplasia or angiomatous involvement.

MR venogram may show enlarged deep collateral (medullary or subependymal) veins with lack of superficial cortical veins.

PET may show increased metabolism in early stages, which can be helpful in surgical planning.

Pachygyria

Findings

CT (Figure 1) and MR (Figure 2) imaging demonstrate the classic patterns of pachygyria, including:
- Smooth and markedly thickened cortex (Figure 1 and Figure 2)
- Broad, flat gyri with shallow sulci (focal or widespread)
- Vertically-oriented and shallow Sylvian fissures
- “Figure-of-eight” appearance of the brain on axial imaging


Diagnosis: Pachygyria


The findings in this case are consistent with pachygyria, which falls under the classification of an embryologic neuronal migration disorder. With pachygyria (synonymous with incomplete lissencephaly), there are focal areas of broad, flat gyri interrupted by a smooth and markedly thickened cortex. The etiology in some cases is linked to genetic abnormality, including mutations in chromosome 17 or Xq22, while others demonstrate no genetic abnormalities. Alternative etiologies for the development of this disorder include intrauterine insult (ischemic, metabolic, or viral such as CMV) during the 12th to 24th week of embryologic development. This results in damage to the germinal matrix and radial glial cells. Radial glial cells act as mechanical guides by which neurons are transported to the outer cortex during development. Damage to these cells results in subsequent malfunction of neuronal cell migration to the outer cortex.


Clinical findings

Onset and severity of symptoms varies, depending on the amount of cortical involvement. However, muscle spasms, hyperreflexia, refractory epilepsy, developmental delay, and mental retardation are common in children afflicted with the disorder.


Radiographic findings

Although CT is adequate in making the diagnosis, as in this case, MRI is more effective in evaluating and differentiating between neuronal migration disorders.

CT and MR imaging demonstrate the classic patterns of pachygyria, including:
- Smooth and markedly thickened cortex
- Broad, flat gyri with shallow sulci (focal or widespread)
- Vertically oriented and shallow Sylvian fissures
- “Figure-of-eight” appearance of the brain on axial imaging

Subarachnoid hemorrhage (SAH) due to left PICA aneurysm

Findings

High attenuation within basilar cisterns and subarachnoid spaces, extending to the Sylvian fissures consistent with hemorrhage. SAH was not seen to extend over the convexities (Figure 1, Figure 2 and Figure 3).
Vertebral artery injection digital subtraction angiography demonstrates an aneurysm of the Left PICA origin.
Figure 6 shows classic “teat” at site of rupture.


Differential diagnosis for subarachnoid hemorrhage (CT findings are diagnostic):
- Trauma
- Aneurysm rupture
- AVM
- Angioma
- Neoplasm
- Cortical thrombosis
- Dissection from intraparenchymal hematoma

Differential diagnosis for cerebral aneurysm (angiographic findings are diagnostic)
DD for saccular aneurysms:
- Developmental/degenerative
- Traumatic pseudoaneurysm
- Mycotic
- Oncotic
- Flow related
- Vasculopathy related
- Drug related)

DD for fusiform aneurysms: Atherosclerosis

DD for dissecting aneurysms:
- Trauma
- Vasculopathy


Diagnosis: Subarachnoid hemorrhage (SAH) due to left PICA aneurysm


SAH is most commonly due to trauma. In the absence of trauma history or correlative findings, presence of SAH necessitates investigation for a cause. Nearly two thirds of these cases will be due to ruptured aneurysm. Clinically, patients experience severe headache. Patients often describe a “sentinel” headache, or prodrome indicating earlier bleeding. Less often, focal or global neurologic findings are present.

SAH is graded based on clinical presentation:
Grade 1) being mild headache
Grade 2) severe headache
Grade 3) mild mental status changes
Grade 4) obvious altered mental status or neurologic change
Grade 5) comatose or posturing

Long-term outcome directly correlates with grade at initial presentation. Of all patients with SAH, roughly 40% die within 24 hours and an additional 10% to 25% within six months. Of the survivors, half will have major long-term neurologic deficits.

Radiographically, high attenuation within subarachnoid spaces (sulci, ventricles, basal cisterns) on a noncontrast CT is the principal finding. Multidetector CT is up to 98% sensitive in the first 24 hours. Degree of SAH is also graded and has prognostic value, as does location of hemorrhage.

Complications of SAH include hydrocephalus, rebleeding, and vasospasm. Hydrocephalus is due to obstructing clot within the ventricular system and may be early or delayed. Early evidence is enlargement of the temporal horns. Rebleeding most often occurs within the first 24 hours, but can occur up to 2 weeks after initial insult. This is found in 20% to 30% of untreated patients and carries up to an 85% mortality. Vasospasm is the most feared complication, resulting in the greatest degree of morbidity and mortality, and affects nearly 40% of all patients. Peak time frame, according to the literature, is four to 12 days, although anecdotal experience from our institution suggests this is often seen earlier. Vasospasm can lead to ischemic events and progression of neurologic deficits.

As discussed, primary nontraumatic SAH is most commonly due to aneurysm rupture. Saccular aneurysms are true aneurysms and are the most common. These are thought to be congenital areas of weakening in arterial walls, which develop over many years into an aneurysm. Fusiform and dissecting are the other two major categories, and are much less common. Aneurysms have a fairly predictable distribution: 35% anterior communicating artery, 30% posterior communicating artery, 20% MCA bifurcation, and 15% vertebrobasilar system. Location of SAH is often a clue to aneurysm location. While no aneurysm is too small to exclude rupture, 4 to 7 mm appears to be the critical size. Aneurysms larger than 10 mm are at much higher risk. A patent aneurysm appears as an outpouching of contrast, while a thrombosed aneurysm may have a normal appearance. Lobulation or irregularity of aneurysm dome (“teat”) is an indication of possible rupture site, especially in the presence of multiple lesions.

Treatment of aneurysms has significantly progressed with intraarterial coil embolization. In the past, the only option was open surgical intervention. Timing of treatment is divided into two phases: early (within two to three days) and late (after ten to 14 days), avoiding the peak incidence of vasospasm. No significant outcome difference has been proven, however, proponents of early intervention for low-grade aneurysms cite the ability for aggressive treatment to lower risk of vasospasm once the aneurysm is controlled. Treatment for asymptomatic, unruptured aneurysms is even more controversial, due to postprocedural complications. Typically, lesions less than 5 mm are followed, while larger lesions are often treated.

Labyrinthitis ossificans

Findings

There is osseous obliteration of the visualized cochlea (Figure 1), vestibule, and lateral semi-circular canal (Figure 2).


Diagnosis: Labyrinthitis ossificans


The most common causative factor is inflammation of the inner ear, secondary to bacterial meningitis and subsequent purulent labyrinthitis. Other, less common causes include labyrinthectomy, temporal bone trauma, autoimmune inner ear disease, sequela of mumps or measles, and otitis media with associated suppurative labyrinthitis.

Ossification in labyrinthitis ossificans commonly occurs primarily at the basal turn of the cochlea, which is the insertion site of the electrodes of cochlear implant devices, and subsequently may interfere with full insertion and successful results. MRI is used to assess for early fibrosis prior to the formation of calcification.