Clinical scenario: Focal seizures | No deficit | Ring enhancing lesion on CT
An 11-year-old boy from a rural community presents with three episodes of focal seizures involving the left arm, followed by secondary generalization over the past 2 weeks. He has no fever, headache, weight loss, or history of tuberculosis contact. His developmental milestones are normal.
On examination, he is conscious and oriented. There are no focal neurological deficits, no meningeal signs, and fundoscopy is normal.
Laboratory investigations:
- Hemoglobin: 11.8 g/dL
- WBC: 7,900/µL
- ESR: 18 mm/hour
- HIV: Negative
MRI brain shows a single 10-mm ring-enhancing lesion in the right frontal cortex with mild surrounding edema and a tiny eccentric hyperintense mural nodule within the cyst.
What is the most likely diagnosis?
A. Brain abscess
B. Neurocysticercosis
C. Tuberculoma
D. Toxoplasmosis
E. Pilocytic astrocytoma
Correct answer & Explanation:
Correct Answer: B. Neurocysticercosis
Explanation:
The child has parenchymal neurocysticercosis, caused by the larval stage of Taenia solium.
The most important clue is the eccentric mural nodule (scolex) within the cystic lesion, which is considered pathognomonic for neurocysticercosis.
Typical features include:
- New-onset focal seizures (most common presentation).
- Solitary or multiple ring-enhancing lesions.
- Mild surrounding edema.
- Minimal systemic symptoms.
- Endemic geographic region.
Why the other options are incorrect
- A. Brain abscess: Usually associated with fever, leukocytosis, marked edema, and significant mass effect.
- B. Neurocysticercosis: Correct. An eccentric scolex within a cystic lesion is highly characteristic.
- C. Tuberculoma: Often appears as a solid or conglomerate ring-enhancing lesion without a scolex and is more commonly associated with tuberculosis exposure or other supportive clinical features.
- D. Toxoplasmosis: Typically occurs in immunocompromised patients and usually presents with multiple lesions.
- E. Pilocytic astrocytoma: Generally presents as a cystic posterior fossa tumor with an enhancing mural nodule rather than a small cortical ring-enhancing lesion causing focal seizures.
Learning Point
For a child with new-onset focal seizures, the finding of a small ring-enhancing lesion containing an eccentric scolex is virtually diagnostic of parenchymal neurocysticercosis.
