Radiography
Findings
On radiographs, calcified cysticerci appear as multiple elongated lesions shaped like cigars or grains of rice. These lesions are arranged in the direction of the muscle fibers in affected skeletal muscle. Calcified cysticerci are easily visualized on soft tissue images. Calcified intracranial cysts are occasionally seen on skull images.
Radiographs have been used as part of the evaluation during ventriculography for the diagnosis of intraventricular neurocysticercosis (NCC) and during myelography for the diagnosis of intraspinal NCC.
Degree of Confidence
CT is more sensitive than plain radiography in detecting intracerebral calcification.
False Positives/Negatives
The presence in the skeletal muscles of multifocal calcifications resembling grains of rice is suggestive of cysticercosis, particularly in patients from endemic areas. A solitary calcification is nonspecific and is of no diagnostic significance.
Computed Tomography
Findings
An inactive lesion represents a dead organism. Such lesions are densely calcified, with no enhancement. CT reveals 1 or more sites of calcification, typically 2-10 mm in diameter (see Image 1).
Active parenchymal neurocysticercosis (NCC) is the most common form of disease. The viable cyst appears as a thin-walled fluid-filled cyst with a mural nodule (live scolex); the cyst causes no inflammatory reaction or edema, and it does not enhance (see Image 2). Symptomatic infection develops when the cysticercus loses the ability to control the host's inflammatory and immune responses.
In the colloid stage, the cyst is encapsulated; it contains a high-protein fluid, and it demonstrates ring enhancement. Often, associated edema or enhancement is noted in the brain parenchyma (see Image 3). As the cysticercus becomes fibrotic or collapses, a focal area of enhancement suggestive of granuloma is seen (granular-nodular stage) (see Image 4). Finally, a focal area of calcification appears. At any stage, solitary or multiple lesions may exist. Multiple cysts are found in 80% of patients (see Image 5). Cysticercal encephalitis results from infection with a large number of cysticerci that induce an intense inflammatory response in the brain parenchyma. Its appearance is that of diffuse cerebral edema with small, slitlike ventricles.
Intraventricular cysts remain clinically silent until they degenerate. The symptomatic form results in obstructive hydrocephalus. Cysticerci may be seen in any of the ventricles. CT scans may reveal evidence of obstructive hydrocephalus or dilatation or distortion of the involved ventricle. CT scans obtained after the intraventricular administration of contrast material delineate the cyst and the site of the obstruction (see Image 6).
There are 3 subtypes of subarachnoid NCC:
- In the first subtype, NCC is located in the gyri of the cerebral convexities; in this subtype, the appearance and presentation of cysticerci may resemble that of active parenchymal NCC.
- In the second subtype, cysticerci are found in the fissures (eg, sylvian fissure); they may measure several centimeters in diameter and are termed giant cysticerci (see Image 7). Giant cysticerci may produce a mass effect or parenchymal inflammation. They are readily detected on CT scans, but small cisternal cysticerci may not be seen.
- In the third subtype, cysticercosis involves the basal cisterns. This subtype is characterized by arachnoiditis; it appears as focal or diffuse meningeal enhancement or as vasculitis with stroke. Patients often develop communicating hydrocephalus (see Image 8).
Spinal NCC may be localized to the subarachnoid space or spinal cord. Degenerating cysticerci become fixed at one level and induce inflammation. CT myelography may demonstrate an extramedullary block or filling defects in the intrathecal contrast column.
Ocular involvement may be intravitreal or subretinal. CT may demonstrate cysts in the extraocular muscles (see Image 9).
Degree of Confidence
In most patients, the diagnosis of neurocysticercosis (NCC) may be reliably made on the basis of CT findings; this is particularly true for patients with multifocal parenchymal disease. In the vesicular stage, MRI is more accurate than CT in detecting an eccentric scolex. Intraventricular cysts are more clearly depicted with CT ventriculography or MRI.
False Positives/Negatives
In most cases, CT scans help in the detection of structural disease, but lesions in the brainstem and small cisternal and intraventricular lesions may be missed. If CT is performed without contrast enhancement, isoattenuating lesions may not be detected. In some asymptomatic individuals, CT findings may be suggestive of neurocysticercosis (NCC).
For cases involving small, ring-enhancing lesions in association with vasogenic edema, the differential diagnosis includes metastases, cerebral abscess, parasitic infection, primary neoplasm, and resolving subacute infarction and hematoma.
Magnetic Resonance Imaging
Findings
On MRIs, the contents of live cysts (vesicular stage) are isointense relative to cerebrospinal fluid (CSF) on T1-weighted images (T1WI) and T2-weighted images (T2WI).14,15
T1WIs clearly show an eccentric, hyperintense, 2- to 5-mm scolex with a pea-in-the-pod appearance (see Image 10). The demonstration of a scolex is pathognomonic of neurocysticercosis (NCC). When the larva begins to die (colloid vesicular stage), the fluid in the cyst becomes more turbid, and it is mildly hyperintense to CSF on both T1WIs and T2WIs. The surrounding edema is hypointense on T1WIs and hyperintense on T2WIs. On T2WIs, the hypointense cyst wall stands out between the hyperintense cyst fluid and edema (see Image 11). The cyst wall may be enhancing in the granular-nodular stage.
Calcified cysts are seen as areas of signal void, especially on gradient-echo images.
All the stages may be seen simultaneously in the same patient.
Cisternal cysts (see Image 12) and intraventricular cysts (see Image 13) are visualized better on MRIs than on CT scans because they stand out in comparison to CSF as a result of the relative T1 shortening. If the cysts induce meningitis, arachnoiditis, or ependymitis, contrast enhancement is clearly noted.
Intraspinal NCC commonly involves the subarachnoid space and, less often, the cord or epidural space.
Contrast-enhanced MRI clearly defines intramedullary and extramedullary cysticerci. Intramedullary NCC usually occurs as a single lesion in the thoracic cord.
Degree of Confidence
MRI is superior to CT in imaging the lesions of neurocysticercosis (NCC), but it is less available than CT in regions of the world where NCC is endemic. MRI is better in detecting cystic lesions in the base of the brain, CSF spaces (eg, ventricular NCC, cisternal NCC), and intramedullary lesions. The scolex may be more readily apparent on MRI than on CT. MRI is superior in demonstrating inflammation around the cyst. The differential diagnosis of spinal intramedullary NCC includes other infectious granulomas and neoplasms.
False Positives/Negatives
A parenchymal cysticercus cyst without a scolex may mimic other cystic lesions. A ring-enhancing lesion with surrounding edema may represent neurocysticercosis (NCC), tuberculosis granuloma, fungal abscess, pyogenic abscess, neoplasm, or resolving hematoma and/or infarct. Rarely, cyst walls are indistinguishable from the CSF in the ventricle or cisterns; in such cases, a preoperative diagnosis may be difficult.
Ultrasonography
Findings
US is useful in the diagnosis of ocular neurocysticercosis (NCC). The cysts are well delineated when they occur in a subretinal location. The cyst wall is well depicted against the vitreous humor, and the cyst elevates the retina.
Degree of Confidence
The degree of confidence in the diagnosis of ocular neurocysticercosis (NCC) depends on expertise of the ultrasonographer. An experienced ultrasonographer can diagnose most NCC lesions of the eyes.
False Positives/Negatives
A cyst without a scolex cannot be differentiated from other cystic lesions of the eye.
Nuclear Imaging
Findings
Nuclear medicine studies are not helpful in the diagnosis of neurocysticercosis (NCC).
Angiography
Findings
Cerebral angiography may be useful in the evaluation of vasculitis resulting from cisternal neurocysticercosis (NCC). Narrowing, occlusion, and the beading of vessels may be seen.
Degree of Confidence
Findings of vasculitis are nonspecific for the diagnosis of neurocysticercosis (NCC).
False Positives/Negatives
Angiographic findings of vasculitis are nonspecific and may be seen in cases of tubercular meningitis, chronic meningitis, and vasculitis related to collagen vascular disease.
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References
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Further Reading
Keywords
CNS cysticercosis, neurocysticercosis, NCC, pork tapeworm, Taenia solium, T solium, CNS parasite, tapeworm, tape worm, cysticercus disease, taeniasis, teniasis, cestode infection, helminthiasis, parasitic disease, meningeal cysts, parenchymal cysts, ventricular cysts
