IMAGING FINDINGS-
Axial T1w MR images shows multiple small focal lesions in supra & infratentorial brain showing small hypointense centre
Few lesions in rt.parietal region shows minimal perilesional edema in coronal FLAIR images
Axial contrast enhanced T1W MR image shows thin peripheral type of enhancement.
Diagnosis – Neurocysticercosis.
- Most common parasitic CNS infestation and also one of the commonest causes of ring enhancing lesion of the brain.
- The larval form of the pork intestinal tapeworm Taenia solium is the agent.
- Humans are the definitive host and usually harbor the adult tapeworm in the small intestine as an asymptomatic infestation.
- Ingestion of the eggs by the intermediate host, pig or man produces oncospheres or primary larvae.
- These bore into the intestinal mucosa and enter the circulation. Hematogenous spread occurs to the neural, muscular and ocular tissue. Once inside the brain, the oncospheres develop into secondary larvae, the cysticerci.
- CNS is infested in 60-90 % of patients.
- Epilepsy- intense inflammatory reaction stimulated by dead larvae.
- Arachnoiditis secondary to invasion of the archnoid by the cysticerci leads to meningeal fibrosis and obstructive hydrocephalus.
- If the inflammatory reaction is florid, a vasculitic syndrome ensues with multiple infarctions.
Four patterns of NeuroCysticercosis:
· Parenchymal
· Subarchnoid,
· Intraventricular
· Mixed.
The parenchymal type is most common, the corticomedullary junction is the primary location.
STAGES:
Manifestations are divided into four stages, patient may have multiple lesions of different stages.
1. Vesicular stage:
Cysticercus consists of a thin capsule that surrounds a viable larva and its fluid containing bladder. The fluid is clear, and little or no inflammatory reaction is present.
On imaging larvum appears as a round CSF like cyst with a mural nodule that represents it scolex.
Edema and contrast enhancement are rare.
Isointense to CSF in all MR sequences. The bright signal of CSF on T2W may obscure the scolex, which is best seen on proton density images.
2. Colloidal vesicular stage:
Larva die, begins to degenerate, cystic fluid becomes turbid and cyst shrinks as its capsule thickens. Degenerating larvum releases metabolic products that disrupt blood brain barrier therefore host imflammatory reaction ensuses & leads to edema and cyst wall enhancement
Cyst fluid hyperintense to CSF on MR imaging.
3. Granular nodular stage:
The cyst retracts, its capsule thickens and the scolex calcifies.
On CT there is isodense cyst with hyperdense calcified scolex. Surrounding edema and contrast enhancement persists.
Iso to brain on T1W and iso to hypo on T2W.
Nodular or micro ring enhancement is common, suggesting granuloma.
Target or bull’s eye appearance with calcified scolex in the centre of the lesion.
4. Nodular calcified stage:
Here Granulomatous lesion has contracted to a fraction of it initial size and is completely mineralized.
Small calcified nodule is seen. No mass effect or enhancement is seen.
Differentials
- Tuberculomas
- Pyogenic Abscess
- Metastases
- NeuroCysticercosis
Tuberculoma
It can be seen as a ring enhancing lesion with calcified nodules
Points against are-
- Cortical, sub cortical and basal ganglia lesions
- Marked cerebral edema common
- Meningitis is commonly seen
· It usually produces the mass effect
Pyogenic Abscess
Can be seen as ring enhancing lesion typically at CMJ
Points against are-
- Cortico medullary junction is the common site
- Marked cerebral edema common
- Abscess rim is thickest near the cortex and thinnest near the ependyma
- Meningitis is commonly seen
- It usually produces the mass effect.
METASTASIS
Points against are-
- Calcification is rare (untreated mets)
- Usually of thick wall
- Location –corticomedullary junction
- H/O known malignancy
(lung>breast>melanoma>GI/GU tumours)