Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

MUSCULOSKELETAL
Year
: 2006  |  Volume : 16  |  Issue : 3  |  Page : 355--357

Pictorial essay: Spinal echinococcosis


SV Phatak 
 Prathima Institute of Medical Sciences, Nagunur road, KARIMNAGAR (A.P.)-505147, India

Correspondence Address:
S V Phatak
Consultant Radiologist, Prathima Institute of Medical Sciences, Nagunur road, KARIMNAGAR (A.P.)-505147
India




How to cite this article:
Phatak S V. Pictorial essay: Spinal echinococcosis.Indian J Radiol Imaging 2006;16:355-357


How to cite this URL:
Phatak S V. Pictorial essay: Spinal echinococcosis. Indian J Radiol Imaging [serial online] 2006 [cited 2020 Feb 28 ];16:355-357
Available from: http://www.ijri.org/text.asp?2006/16/3/355/29016


Full Text

 INTRODUCTION



Human echinococcosis is a zoonotic infection caused by larval forms of the genus Echinococcus inhabiting the small intestine of carnivores. A total of four different organisms can cause echinococcosis in humans. Echinococcus granulosus which causes cystic echinococcosis (Hydatid disease), Echinococcus multilocularis which causes alveolar echinococcosis (alveolar hydatid disease), Echinococcosis vogeli which causes polycystic echinococcosis and Echinococcus oliganthrus which causes Oliganthrus echinococcosis. [1] Hydatid disease is a significant problem in underdeveloped regions of world where animal husbandry is common but without veterinary control. [2] Hydatid disease of spine occurs in 1%of all cases with hydatidosis and is most commonly located in dorsal spine. [3] Dorsal spine is involved in approximately 50% cases. This is followed by Lumbar spine (20%), Sacral (20%) and cervical spine (10%)[2] The disease occurs either by direct extension from a pulmonary infestation or less commonly begins primarily in vertebral body. [3]

 DISCUSSION



Spinal hydatid disease is classified into five groups. Intramedullary, Intradural extramedullary, Extradural intraspinal, Vertebral and Paravertebral. [2],[4],[5] The first three groups of hydatid disease are rare. Hydatid cysts are typically multiple when located in spinal cord. CT and MR demonstrate a lesion with imaging characteristics similar to those of cerebrospinal fluid. In contrast to hydatid cysts located within brain, spinal hydatid cysts demonstrate no rim enhancement after contrast material injection. Calcification is also rare in spinal hydatid cyst. [2] There are no pathognomonic signs and symptoms of spinal hydatid disease. If spinal hydatid disease is not caused by encroaching pulmonary lesions it often begins in vertebral body. The parasite grows multilocularly because of lack of defensive reaction.of bony tissue. When the cyst breaks out of vertebral body anteriorly or laterally it may extend into extradural space or any of the paraspinal tissue [3] Hydatid disease in bone differs from soft tissue disease in that growth occurs along the line of least resistance, particularly along the intratrabecular spaces. As the larvae enlarge there is dilatation of the bony spaces in spongiosa and resorption of cancellous bone. Enlargement and spread is achieved partially by local pressure erosion of bone while pressure on blood vessels may result in local bone necrosis. Marked fragmentation and absorption is not seen prominently which is a feature in bacterial osteomyelitis and destructive neoplasm. There is no development of adventitious layer or pseudocapsule. In bone, cysts expand relatively slowly. Bony expansion does not occur; erosion through bone and periosteum into adjacent soft tissues proceed without stimulating subperiosteal new bone formation. Cysts in paravertebral soft tissue behave as they do in other soft tissues. Each cyst enlarges radially and endogenous vesiculation results in formation of daughter cysts within parent cyst. An adventitious layer forms. [5] Plain radiographic findings of spinal hydatidosis are nonspecific and may show bone destruction and sometimes-abnormal soft tissue masses in paravertebral region. CT clearly shows the destructive changes as well as paraspinal soft tissue involvement. Spinal canal cystic involvement can not be accurately evaluated due to lack of appreciable contrast difference between the dural sac and its contents.[6]MRI is highly sensitive in detecting cysts particularly in extradural and intradural compartments owing to its high contrast resolution.It is the modality of choice in evaluating the extent of the disease in the spinal and paraspinal compartments as it can precisely define detailed anatomical relationship of cystic lesions.No other lesion has similar appearance on MRI.Hydatid cysts have two dome shaped ends,no debris in their lumen and look like a flattened sausage,occasionally they are spherical.Their walls are very thin ,regular without septations.Extradurally they are always multiple and involve bone.Intradurally they may be single or multiple.[6]Cysts on T1 weighted images have inhomogenous,low signal intensity and hyperintense on T2 weighted images.[7]They are easily differentiated from arachnoiditis,which has irregular shape and is often septated.Apart from the prime modality for diagnosis and operative planning , MRI has great advantage in assessing immediate post operative results in demonstrating residual disease.[6],[7]T1 weighted sequences are highly sensitive in detection of all cysts and their relationship to various spinal compartments particularly intradural and extradural regions.[6]

References

1Elmar M.Merkle et al musculoskeletal involvement in cystic Echinococcosis: Report of eight cases and review of literatureAJR 1997; 168:1531-1534.
2Pinar Polat et al Hydatid disease from head to toe Radiographics2003; 23:475-494.
3Ismail H.Tekkok, Kemal Benli Primary spinal extradural hydatid disease: report of a case with magnetic resonance characteristics and pathological correlation Neurosurgery vol.33, No.2 August 1993:320-322.
4S.Gupta, V.Rathi, S.K.Bhargava Unilocular primary spinal Extradural hydatid cyst -MR appearance Ind.J.Radiol Imag2002 12:2:271-273.
5Peter A.Braithwaite, Richard F.LeesVertebral hydatid disease: Radiological assessment Radiology September 1981; 140:763-766.
6Mohieddine Fahl et al Magnetic resonance imaging in intradural and extradural spinal echinococcosis Clinical Imaging 1994; 18:179-183.
7Scott W.Atlas Magnetic resonance imaging of brain and spine vol.1, third edition Lippincott Williams and Wilkins 2002:1947-1952.