Hydatid Cyst of the Brain: A Rare Neurosurgical Entity and Its Radiologic Diagnosis

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 Hydatid Cyst of the Brain: A Rare Neurosurgical Entity and Its Radiologic Diagnosis

뇌의 포낭낭: 드문 신경외과적 질환 및 방사선학적 진단

Keywords: cerebral hydatid cyst, brain parasitic infection, intracranial cystic lesion MRI, hydatid disease neurology, echinococcosis CNS, cerebral imaging quiz, parasitic cyst differential diagnosis

1. Introduction

Hydatid disease, or echinococcosis, is a parasitic infection caused primarily by Echinococcus granulosus. While commonly affecting the liver and lungs, involvement of the central nervous system (CNS) is exceedingly rare, accounting for less than 2% of all hydatid cases. Among these, isolated cerebral hydatid cysts, especially in adults, are considered extraordinary occurrences and pose diagnostic and therapeutic challenges.

In this expert-level column, we present a deep dive into the radiologic and clinical evaluation of intracranial hydatid cysts, with emphasis on differential diagnosis, management, and radiologic pearls. Based on the case described in the Journal of the Belgian Society of Radiology, we highlight the key MRI findings and provide quiz questions for educational reinforcement.

2. Pathophysiology and Clinical Relevance

Hydatid cysts form as a result of larval migration through systemic circulation. In cerebral involvement, larvae bypass hepatic and pulmonary filtration systems, reaching the brain, most frequently localizing in the middle cerebral artery territory. The cysts grow slowly and may remain asymptomatic for years until reaching a size large enough to cause mass effect.

Common clinical manifestations:

  • Raised intracranial pressure (ICP)

  • Headache

  • Seizures

  • Focal neurological deficits

3. Radiologic Features

3.1 MRI Characteristics

MRI remains the gold standard for evaluating intracranial hydatid disease. Typical features include:

  • T1-weighted imaging: Hypointense lesion relative to brain parenchyma

  • T2-weighted imaging: Hyperintense cystic lesion with well-demarcated margins

  • No perilesional edema (important differentiator from abscess or neoplasm)

  • No contrast enhancement unless secondary infection is present

  • Mass effect without infiltration

[Figure]

Axial T2‑ and FLAIR‑weighted images show a large intra‑axial cyst in the left frontoparietal region with signal intensity identical to cerebrospinal fluid. There is a significant mass effect with right‑sided midline shift, but remarkably little surrounding edema (arrows)


DWI images and ADC map show no diffusion restriction.

Axial and sagittal T1‑weighted images after contrast administration show slight rim enhancement at the parietal side (arrow), probably reactive to a focal breach in the cyst wall with the formation of a daughter cyst (arrowheads).


4. Differential Diagnosis

4.1 Arachnoid Cyst

  • CSF-equivalent signal on all sequences

  • Typically extra-axial and does not cause parenchymal shift unless large

4.2 Brain Abscess

  • Ring-enhancing lesion

  • Edema and restricted diffusion on DWI sequences

4.3 Cystic Glioma or Metastasis

  • Irregular walls

  • Associated solid components and contrast enhancement

4.4 Neurocysticercosis

  • Multiple small cysts, often with a visible scolex

  • Parenchymal calcifications common

5. Management

Surgical excision is the primary treatment, aiming for en bloc resection to prevent rupture and anaphylaxis reaction. Preoperative and postoperative antihelminthic therapy (e.g., albendazole) is standard to prevent recurrence.

Important surgical considerations:

  • Avoid cyst rupture to prevent dissemination

  • Use of Dowling’s technique (gravity-assisted enucleation) is preferred

Quiz

Based on the referenced image [Figure], test your diagnostic acumen with the following questions.

1. Which imaging feature strongly suggests a hydatid cyst rather than a neoplastic lesion?

A. Contrast enhancement
B. Perilesional edema
C. No enhancement with sharply demarcated margins
D. Intracystic hemorrhage

2. What is the most appropriate management approach for a large, symptomatic cerebral hydatid cyst?

A. High-dose steroids
B. Needle aspiration
C. Surgical excision with intact cyst removal
D. Gamma knife radiosurgery

3. Which of the following MRI features helps differentiate a hydatid cyst from a cerebral abscess?

A. T2 hyperintensity
B. Midline shift
C. Ring enhancement and restricted diffusion
D. Well-defined margins

Answer & Explanation

1. Correct Answer: C. Explanation: Hydatid cysts typically show no contrast enhancement and have well-defined borders, unlike tumors, which enhance and often show surrounding edema.

2. Correct Answer: C. Explanation: Surgical excision with intact cyst removal is necessary to avoid rupture and potential anaphylaxis. Needle aspiration is contraindicated due to the risk of dissemination.

3. Correct Answer: C. Explanation: Cerebral abscesses usually demonstrate ring enhancement and diffusion restriction, unlike hydatid cysts, which lack both.

6. Case Learning Points

  • Unusual presentation in adults: Consider hydatid cyst even in non-endemic regions when the lesion is cystic, well-circumscribed, and lacks enhancement.

  • MRI superiority: MRI allows clear visualization of the lesion and planning of the surgical approach.

  • No surrounding edema: A crucial radiologic clue.

  • Watch for midline shift: Despite the absence of invasion, cysts can grow large and displace critical structures.

7. Public Health and Prevention

Hydatid disease remains endemic in parts of Africa, South America, the Middle East, and the Mediterranean. CNS involvement may occur due to poor sanitation and close contact with infected canines. Public education, veterinary control, and meat inspection are vital components of control.

8. Conclusion

Cerebral hydatid cysts, although rare, should be considered in the differential diagnosis of intracranial cystic masses, especially in patients from endemic areas. Accurate radiologic identification using MRI can prevent misdiagnosis and guide life-saving surgery. Radiologists and neurosurgeons must maintain a high index of suspicion and collaborate closely for optimal outcomes.

Referencestext

[1] T. Kaya et al., “Primary cerebral hydatid cyst: case report and review,” Acta Neurochir (Wien), vol. 142, pp. 293–296, 2000.
[2] A. Arana-Iniguez and M. San Julian, “Cerebral hydatid disease: review of literature,” J Neurol Neurosurg Psychiatry, vol. 20, pp. 19–25, 1957.
[3] R. Turgut, “Hydatid disease of the CNS: diagnosis and treatment,” J Neurosurg Sci, vol. 48, no. 4, pp. 171–177, 2004.
[4] A. Elshafie, M. Ahmed, and H. Alkhawajah, “MRI findings in cerebral echinococcosis,” Neuroradiology J, vol. 26, no. 1, pp. 80–83, 2013.
[5] H. Altinors et al., “Central nervous system hydatidosis in Turkey,” Neurosurgery, vol. 24, no. 2, pp. 199–204, 1989.
[6] A. Pedrosa et al., “Hydatid disease: radiologic and pathologic features and complications,” Radiographics, vol. 20, no. 3, pp. 795–817, 2000.
[7] S. Tekin et al., “Management of brain hydatid cysts: surgical strategy and long-term outcome,” C

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