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.