Fact-sheet: Echinococcus of bone
Updated on 04/19/2018 at 8:10 AM
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Definition
Osseous echinococcosis is an anthropozoonosis caused by the larval form of a cestode of the species Echinococcus granulosus.
A rare localization of this parasitic infection.
The parasite must successively pass through the hepatic and pulmonary selective filters before it can become established in bone tissue.
Osseous hydatid cysts do not present a pericystic membrane.
Involvement predominates at the vertebral level.
Clinical features
Nonspecific clinical signs:
- Local swelling, rapidly enlarging, most often painless.
- Radicular or spinal cord deficit syndrome.
CT
Bone lesions:
- Hypodense lytic images of variable size and shape, more or less well-defined, without enhancement after contrast injection.
- Paraosseous extension: simple cystic/abscess/heterogeneous pseudotumoral appearance
- Possible contiguous joint involvement
MRI
MRI is the imaging modality of choice for spinal locations and for follow-up after treatment.
- Hydatid vesicles of oblong shape, resembling a "flattened sausage," with thin walls. Pure fluid signal. Vesicles are always multiple in extradural locations.
- Homogeneous or heterogeneous appearance, isointense on T1 and hyperintense on T2*/T2.
- Sometimes a multiloculated appearance with numerous vesicles of fluid signal.
Management
Ultrasound- or CT-guided puncture is contraindicated due to the risk of seeding.
Diagnosis = pathological examination of a surgical resection specimen or percutaneous biopsy.
Differential diagnosis
- Primary or secondary malignant bone disease (given the poorly defined osteolysis).
- Infectious involvement (tuberculosis, pyogenic, actinomycotic)
- Benign bone tumor (Lodwig type IA)