Spinal hydatid disease is an uncommon manifestation of hydatid disease, caused by the larval stage of Echinococcus granulosus, or less commonly E. alveolaris or E. multilocularis, and describes a spectrum of disease involving the spinal cord, the spine, or both.
For a general discussion, and for links to other system specific manifestations, please refer to the article on hydatid disease.
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Epidemiology
Hydatid disease is endemic in numerous regions of the world, including the Mediterranean region, the Middle East, Africa, the eastern part of Turkey, Australia and parts of South America 1,2. Spinal hydatid disease is uncommon and most commonly affects the thoracic spine, although any part of the spine can be affected 1,2.
Clinical presentation
Although often asymptomatic, clinical signs and symptoms often include 1-3:
back pain
radiculopathy
paraparesis
The most significant complication and presentation of spinal hydatid disease is spinal cord compression 1-3. Furthermore, rupture of a spinal hydatid cyst can result in a type 1 hypersensitivity reaction such as anaphylaxis 2.
Pathology
Hydatid disease is acquired via contaminated food with eggs of the Echinococcus spp. tapeworm 1,2. The oncospheres released from the eggs in the bowel enter the portal circulation, thus usually affecting the liver, but also affecting other sites via hematogenous spread 1,2.
Spinal hydatid disease is thought to occur via three possible mechanisms 1:
hematogenous spread directly to spinal structures (most common)
direct invasion from extraspinal structures
infection secondary to cerebrospinal fluid seeding due to ruptured cysts of cerebral hydatid disease
Classification
Spinal hydatid disease can be anatomically classified according to the Dew/Braithwaite and Lees classification 1,4:
type 1: intramedullary
type 2: intradural, extramedullary
type 3: extradural, intraspinal
type 4: vertebral
type 5: paravertebral
Under this classification, types 1 and 2 are very rare, with 90% of cases being instead confined to the bone and extradural space 1. However, multiple types can also co-exist 1.
Radiographic features
CT
Bony disease has very similar features to vertebral osteomyelitis, however, tends to not demonstrate any osteoporosis and sclerosis, and has an absence of damage to the vertebral discs 1,2,5. The cysts themselves have a similar density to cerebrospinal fluid and very rarely demonstrate calcification 6. CT may also reveal the underlying etiology if spinal hydatid disease is secondary to direct invasion from extraspinal structures 1,2.
MRI
MRI is a more sensitive tool for diagnosing spinal hydatid disease 1,2. Generally, spinal hydatid cysts tend to have a tube-like shape, rather than the classic spherical-shaped cysts that are seen elsewhere in the body and do not have associated perilesional edema 1,2. They also demonstrate similar signal characteristics to cerebrospinal fluid in all pulse sequences 1,2:
T1: hypointense cyst with an iso- or hypointense cystic wall
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T2: hyperintense cyst with a hypointense cystic wall
upon inactivation, it has been reported that cysts tend to lose their hyperintensity and their walls lose their hypointensity
T1 C+ (Gd): shows wall enhancement, although this may be subtle
Treatment and prognosis
The cornerstone of spinal hydatid disease management is surgery, the most common procedure being simple decompression with laminectomy 2,7. Surgery is often an emergency due to spinal cord compression either being the presenting feature or being an impending complication 2,7. Due to high rates of bone involvement in spinal hydatid disease, cyst rupture is often common during surgery which would allow for further seeding of the disease, and thus the spinal hydatid disease tends to be recurrent in nature 2. Pharmacotherapy, with agents such as albendazole, may have a role in reducing the risk of recurrence postoperatively 2.
Differential diagnosis
Considerations include 1,2,5:
vertebral pyogenic infection (osteomyelitis)
spinal malignancy or metastasis
cystic lesions of the spinal cord (large list of differentials)
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