Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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November 30, 2017
Intraorbital Hydatid Cyst
- Background:
- The infestation of the orbit by Echinococcus is an extremely rare phenomenon. The prevalence is estimated to be about 0.61-2/100000 population. It is widespread in some regions, such as the Middle East, New Zealand, Australia, South America and the Mediterranean region, and is related to breeding cattle and dogs together.
- There is capsular fibrosis due to sluggish growth in the wall, which has 2 layers—an outer, laminated ectocyst that functions as a barrier layer and an inner, germinal layer that contains daughter cysts.
- Clinical Presentation:
- Presents with variable symptoms depending on the areas/organ involved
- Key Diagnostic Features:
- Type I: simple, clear cyst with no internal architecture
- Type II: cyst with daughter cyst(s) and matrix
- Type II A: daughter cysts at the periphery
- Type II B: irregular, large daughter cysts occupying almost the entire volume of the mother cyst
- Type II C: oval-shaped with scattered calcifications and few daughter cysts
- Type III: calcified cyst or dead cyst
- Type IV: reserved for ruptured cysts
- Separation of the laminated membrane from the pericyst produces a split wall or floating membrane appearance.
- Differential Diagnoses:
- Abscess: These show a thick, regular-enhancing wall with central diffusion restriction. There are associated inflammatory changes in the soft tissues. Superior ophthalmic vein may be thrombosed.
- Mucocoele: Nonenhancing cystic mass that is usually low on T1W and high on T2W, with occasional heterogeneous signals depending on inspissated secretions. There is associated bone remodelling.
- Lymphangioma: There are multiple loculations with fluid-fluid levels. There is no diffusion restriction and no susceptibility artifact.
- Lacrimal tumors: These are solid, enhancing masses arising from the lacrimal gland at the superolateral aspect of the orbit. Diffusion restriction may vary according to the histology and cellular density (lower in lymphomas than in parenchymal tumors), but is not as pronounced as in abscesses. Susceptibility on SWI is not usually seen.
- Treatment:
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Surgery is the first treatment choice.
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