British Journal of Radiology (2004) 77, 338-341
© 2004 British Institute of Radiology
doi: 10.1259/bjr/47590426
Echinococcosis of the rib with epidural extension: a rare cause of paraplegia
A A Raut, MD
A M Nagar, DMRD
R S Narlawar, DMRD
V L Bhatgadde, MBBS
M N Sayed, MBBS
and
P Hira, DNB
Department of Radiology, K.E.M Hospital, Acharya Dhonde Marg, Parel, Mumbai-400012 India
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Abstract
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Skeletal echinococcosis is a relatively rare entity and that of the rib is exceptional. Less than 50 cases of costal echinococcosis have been reported in the literature so far. Accurate pre-operative diagnosis aids in appropriate management and helps to eradicate the disease. This also prevents the dissemination of parasite and further complications. We report a case of echinococcosis of the rib with epidural extension in a young adult who presented with paraparesis and back pain. His laboratory investigations were within normal limits. Plain radiographs of the dorsal spine, CT scan of thorax and MRI of dorsal spine were performed. The imaging features were suggestive of echinococcosis involving the rib with epidural extension. The cyst was completely resected. Histopathology of the resected specimen confirmed the diagnosis of echinococcosis.
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Introduction
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Human echinococcosis is a zoonotic infection caused by Echinococcus granulosus [1]. The exact incidence is not known and depends on the endemicity of the disease. Liver and lung are the sites affected primarily, with musculoskeletal affection in only 1–4% of the cases [2, 3] and occur as an isolated finding. The course of the disease is generally slow and laboratory tests are frequently non-specific [4]. The diagnosis is made through the combined assessment of clinical, radiological and laboratory findings [4, 5]. The role of imaging in this condition is to distinguish it from aneurysmal bone cyst, giant cell tumour and metastasis so that appropriate surgical procedure can be performed to prevent anaphylactic shock, which may be a fatal complication of surgery. This also prevents surgical dissemination of the parasites [6].
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Case report
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A 28-year-old farmer presented with gradually increasing pain on the right side of the back, radiating to the infra-axillary region for a period of 6 months. There was history of gradually progressing paraparesis over 3 months. There was no history of trauma. On examination, a localized bulge over the back on the right side was noted which was tender on palpation. There was no sensory deficit, but bilateral distal motor weakness was noted. His routine laboratory investigations were normal. Frontal radiograph of the dorsal spine (Figure 1
) showed an expansile lytic lesion at the head of the ninth rib on the right side, causing destruction of the superior and inferior cortices of the rib. The right ninth pedicle was also eroded. There was no calcification, sclerosis or any periosteal reaction. Plain and contrast enhanced CT scan of the thorax (Figure 2) showed a well-defined, non-enhancing, multiloculated, expansile lytic soft tissue mass at the same level. This lesion showed increased peripheral attenuation and was completely non enhancing following contrast administration. It was also causing destruction of the right pedicle and transverse process of the D9 vertebra (Figure 3). The soft tissue mass was seen to extend into the extradural compartment causing compression of the thecal sac. Lung parenchyma and the upper abdominal structures were unremarkable. On T1 weighted MRI, there was a well-defined, multiloculated, hypointense lesion of uniform signal intensity which on T2 weighted images (Figures 4 and 5) showed a high signal intensity. The lesion could be identified extending in the extradural space, impinging on the thecal sac (Figures 4 and 5). Ultrasound examination of the abdomen and pelvis was normal. Fine needle aspiration biopsy of the lesion under CT guidance was performed which confirmed the diagnosis of echinococcosis. Patient underwent complete excision of the cyst and decompression of the cord. Post-operative recovery was uneventful. There was gradual recovery of lower limb power and patient was discharged on the 15th post-operative day on antihelminthic treatment. Gross pathological examination of the surgical specimen revealed multiple cysts ranging in size from 0.5 cm to 2 cm, pearly white in colour containing clear fluid and bone bits within. Histopathology of the specimen showed lamellated cyst wall with inflammatory reaction.
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Figure 1. Plain radiograph of the dorsal spine shows an expansile lytic lesion without cortical breakthrough along the posterior aspect of the right 9th rib.
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Figure 2. Axial contrast enhanced CT scan of thorax shows a multiloculated, sharply defined, cystic lesion along the posterior aspect of the right 9th rib with epidural extension.
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Figure 3. Axial bone window image at the same level showing expansile lytic lesion of the rib with destruction of adjacent transverse process. There is no calcification or sclerosis.
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Figure 4. Axial T2 weighted MR image showing homogeneous high intensity multicystic lesion along the posterior aspect of the right 9th rib with epidural extension and impingement of the cord.
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Figure 5. Sagittal T2 weighted MR sequence demonstrating the extradural involvement with compression of the thecal sac.
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Discussion
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Human echinococcosis is a zoonotic infection caused by larval forms (metacystodes) of genus Echinococcus inhabiting the small intestine of carnivores [1]. Genus Echinococcus comprises of two species: Echinococcus granulosus and Echinococcus multilocularis. The former is the most common frequently encountered type of hydatid disease in humans. Osteohydatidosis is caused by the larva of Echinococcus granulosus which is usually transmitted from dogs and other carnivorous animals to man. Osteohydatidosis has typically a multiloculated appearance due to the solid structure and tensile nature of bone. Graver forms of echinococcosis cause multiloculated lesions in soft tissues and viscera especially the liver. These forms are usually caused by Echinococcus multilocularis [6]. Echinococcus granulosus is extremely widespread with high rates of infection in eastern and southern Europe, Middle East, North Africa and South America [4]. The incidence of overall bone involvement in hydatid disease is 1–4% and involvement of the thoracic cage is uncommon [4]. Osseous involvement in hydatid disease is most commonly seen in the spine and pelvis, followed by the femur, tibia, humerus, skull and ribs [7, 8]. The exact incidence of rib echinococcosis is not known. In osteohydatidosis, absence of pericyst formation allows aggressive proliferation of the parasite along the lines of least resistance, especially along the bone canals [8]. The parasite growth, gradually replaces the osseous tissues between the trabeculae and eventually destroys the cortex to involve the surrounding tissues [8]. The natural course of costal echinococcosis starts when the larvae lodge in the rib and buds start vegetating out of the mother cyst to produce a multilocular cavity with diverticular extensions. This process invades the spongiosa of the bone in all possible directions. The primary rib lesion is multiloculated and osteolytic which continues to grow slowly. This lesion may then involve adjacent organs such as vertebra, pleura and soft tissues. If this lesion breaks through the cortical portion of the rib, it produces soft tissue masses or abscesses [6].
The posterior ends of the ribs are most commonly involved in costal echinococcosis. Cysts grow along the long axis of the rib causing expansion of the cortex where it meets more resistance from the solid cortical portion of the rib [5, 6].
Costal echinococcosis may be classified as an intraosseous form and an extraosseous form. The intraosseous form may be further classified into a solitary costal form and a costovertebral form. The solitary costal form represents an area of multiloculated rib destruction without periosteal reaction or soft tissue swelling. This lesion is not self limiting but gradually grows in all directions. The costovertebral form is an extension of the disease process into the adjacent vertebra. In many cases the disease involves the spine primarily and the disease extends into the neighbouring rib and costal cartilage. This form is frequently associated with paraspinal soft tissue swelling. The extraosseous form is secondary, which involves the rib by contiguity [6]. The mechanism of involvement is by pressure erosion of the rib(s). Sclerosis of the neighbouring segment of eroded rib(s) is seen in this form [6]. The extraosseous form is most commonly seen due to rupture of pulmonary cyst, either spontaneously or during surgery [9]. Plain radiographs of costal echinococcosis shows an area of multiloculated rib destruction without periosteal reaction or soft tissue swelling. The rib is expanded with preservation of the cortical margins and absence of sclerosis, but when present, it is suggestive of secondary infection [6]. Pathological fracture of the rib may also occur. The rib lesion may extend further to involve the adjacent vertebra. Plain radiograph may show soft tissue calcification in up to 38% of patients. The appearance of calcification may depend on duration of the disease and its clinical course. Calcification represents dystrophic changes in dead parasites. Intraosseous disease rarely demonstrates calcification whereas extraosseous cysts may calcify [8]. Calcification is also an exception to the rule in cases of pulmonary hydatid cysts which rarely calcify [10].
In advanced cases it is difficult to judge the epicentre of the lesion and most of such cases have been reported as primary spinal lesions [11, 12]. Early development of neurological signs may point to the primary site of infection [6]. CT scan provides the precise anatomical details of the lesion along with bone destruction and definition of paraspinal and intraspinal extension of the same [13]. Lesions of echinococcosis generally do not enhance following contrast administration [13]. Delineation of intraspinal extension is also possible with computer assisted myelography although MR scores over CT in this regard [13]. MR is helpful in verifying the extent of the disease, texture of the cyst, degree of medullary involvement [14] and viability of cyst [15].
On T1 weighted images, there is a mixed morphological appearance. High signal intensity content of the cyst may correlate with high cell or protein content which is suggestive of extensive parasite–host reaction [1]. Daughter cysts are more hypointense than the parent cyst on T1 weighted images [15]. The cyst wall or capsule is seen as a low intensity rim, which shows mild enhancement following intravenous gadolinium.
On T2 weighted imaging the daughter cysts are of slightly higher signal intensity than the parent cyst. Signal intensities may change with coexisting infection, calcification or haemorrhage. Extradural spread of the hydatid cysts through a widened neural foramen into the muscle planes may result in a "bunch of grapes" appearance. The T2 weighted sequence indicates whether a cyst is viable or not. A decrease in hyperintensity and an increase is hypointensity from collapsed cyst wall is suggestive of succumbed cyst [15]. Both CT and MR may show endovesicular daughter cysts, which are frequently observed in hepatic disease but are rare in musculoskeletal manifestations of this disease [1].
The differential diagnosis of such a radiographic picture includes giant cell tumour, osteolytic metastases, plasmacytomas, aneurysmal bone cyst and cystic neurofibromas [6].
Biopsy is contraindicated in echinococcosis due to fear of dissemination of scolices and other potentially fatal complications [6]. However, review of recent literature suggests that aspiration cytology is the procedure of choice in suspected cases of skeletal echinococcosis [2].
The gold standard in the therapy of this disease is the radical resection of the rib(s) involved. It has been proposed that better results are obtained by combining surgery with antihelminthic drugs like mebendazole or albendazole. In isolated infestation of a musculoskeletal region, extensive curative surgical treatment combined with antihelminthic treatment for a period of 3 months should be considered [1]. However there are sporadic case reports of percutaneous aspiration of these cysts using ultrasound or CT guidance with pre-medication with albendazole [16]. Large doses of antihelminthic drugs for both pre-operative treatment and postoperative prophylaxis helps in the reduction of recurrence of this disease [4].
In cases of osseous hydatidosis, even after radical removal of the parasites, the World Health Organization (WHO) suggests adjuvant chemotherapy with mebendazole or albendazole for at least 2 years after surgery. In cases where only a palliative treatment is possible, the antihelminthic drug administration can be continuous [17].
Received for publication January 23, 2003.
Revision received June 3, 2003.
Accepted for publication August 20, 2003.
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References
|
|---|
- Merkle EM, Schulte M, Vogel J, Tomczak R, Rieber A, Kern P, et al. Musculoskeletal involvement in cystic echinococcosis: report of eight cases and review of the literature. AJR Am J Roentgenol 1997;168:1531–4.[Abstract/Free Full Text]
- von Sinner WN. Case of primary osseous pelvic hydatid disease. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 1991;155:88–90.[Medline]
- Rieber A, Brambs HJ, Friedl P. CT in echinococcosis of the lumbar spine and paravertebral structures. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 1989;151:371–80.[Medline]
- Karaoglanoglu N, Gorguner M, Eroglu A. Hydatid disease of the rib. Ann Thorac Surg 2001;71:372–3.[Abstract/Free Full Text]
- Rong SH, Nie ZO. Hydatid disease of bone. Clin Radiol 1985;36:301–5.[CrossRef][Medline]
- Bonakdarpour A, Ali Zadeh YF, Maghssoudi H, Shariat S, Levy W. Costal echinococcosis. Report of six cases and review of literature. AJR Am J Roentgenol 1973;118:371–7.[Abstract]
- Pedrosa I, Saiz A, Arrazola J, Ferreiros J, Pedrosa CS. Hydatid disease: radiologic and pathologic features and complications. Radiographics 2000;20:795–817.[Abstract/Free Full Text]
- Beggs I. The radiology of hydatid disease. AJR Am J Roentgenol 1985;145:639–48.[Free Full Text]
- Ozdemir N, Akal M, Kutlay H, Yavuzer S. Chest wall echinococcosis. Chest 1994;105:1277–9.[Abstract]
- Jerray M, Benzarti M, Garrouche A. Hydatid disease of the lungs. Am Rev Respir Dis 1992;146:185–9.[Medline]
- Lagrot F, Costagliola M, Micheau P, Migueres J, Jover A. Costal echinococcosis, a rare form of bone echinococcosis. Apropos of a case. Ann Chir 1969;23:C607–14.[Medline]
- Murray RO, Haddad F. Hydatid disease of spine. J Bone Joint Surg 1959;41:499–506.
- Braithwaite PA, Lees RF. Vertebral hydatid disease: radiological assessment. Radiology 1981;140:763–6.[Abstract/Free Full Text]
- Savas R, Calli C, Alper H, Yunten N, Usten EE, Ertugrul G, et al. Spinal cord compression due to costal echinococcus multilocularis. Comput Med Imaging Graph 1999;23:85–8.[CrossRef][Medline]
- Gupta S, Rathi V, Bhargava SK. Unilocular primary spinal extradural hydatid cyst–MR appearance. Ind J Radiol Imag 2002;2:271–3.
- Brigic E, Zerem E, Terzic S. Ultrasonographic guidance of percutaneous drainage as a new method of treatment of echinococcal cysts. Med Arch 2003;57:13–5.
- Diedrich O, Kraft CN, Zhou H, Sommer T, Perlick L, Schmitt O. Othopedic aspects of osseous echinococcosis—radiologic diagnosis, current surgery and drug therapy aspects. Z Orthop Ihre Grenzgeb 2001;139:261–6.[Medline]
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Abstract
Introduction
