Eur. Radiol. 7, 1207–1210 (1997)  Springer-Verlag 1997

European Radiology

Original article CT and MRI in vertebral hydatid disease I. Tsitouridis, A. S. Dimitriadis Department of Radiology, AHEPA University Hospital, GR-546 36 Thessaloniki, Greece Received 16 August 1996; Revision received 12 November 1996; Accepted 15 January 1996

Abstract. We present the CT and MRI findings of 12 cases with vertebral hydatid cysts. All except 3 patients were admitted with neurological symptoms. The CT and MRI findings and their correlation with pathologic and histologic findings are included. The purpose of this study was to demonstrate the usefulness of CT and MRI in the evaluation of vertebral hydatid disease, detection of the various stages of hydatid cyst, and characterization of the lesion as well in monitoring and planning of the surgical approach. Although MRI is the method of choice, we emphasize the complementary role of these two techniques for the evaluation of vertebral echinococcosis.

with CT and MRI over the past 3 years. Plain radiographs were the first examination before CT and MRI. The CT scans were performed using an EMI 7070 and a Philips Tomoscan SR6000 (Philips, Eindhoven, The Netherlands). The slice thickness was 3 mm and we took images before and after the intravenous administration of 100 ml contrast medium. The MRI exams were performed using an MR imager at 1.5 T (Gyroscan S15/ACS, Philips, Eindhoven, The Netherlands) and T1-weighted, postgadolinium T1-weighted, T2-weighted, and gradient-echo T2weighted image sequences in transverse and sagittal planes (slice thickness 3 mm, matrix 220 × 256, field of view 12–15 cm, two acquisitions).

Key words: Echinococcus – Hydatid cyst – Spine Results Introduction Hydatid disease of the vertebral column is very uncommon, although vertebral involvement is the most common location of skeletal involvement [1]. Difficulty arises in diagnosis because bone involvement in the majority of cases is primary in origin and the Casoni and latex test are unreliable in cases of bone involvement. Computed tomography and MRI examinations determine the extent of the lesion, the relation to the spinal canal, and the preoperative planning of the surgical approach to hydatid cyst. The values and limitations of CT and MRI in the evaluation of vertebral hydatid disease are discussed. Materials and methods Twelve patients (2 women and 10 men; age range 42– 72 years) with vertebral hydatid disease were evaluated Correspondence to: I. Tsitouridis

The 12 vertebral hydatid cysts were located in various parts of the vertebral column (3 in the cervical spine, 8 in the thoracic spine, and 1 in the lumbar spine). The vertebral hydatid cyst in 9 cases involved only a part of the vertebra, with the rest of the cyst lying outside (Fig. 1). In 2 cases there was an extent into the spinal canal from the vertebral body. Many daughter cysts were in the canal and there was spread of the disease into soft tissue of the posterior parts of the vertebrae, spread into the intervertebral foramen (Fig. 2). In 1 case the hydatid cyst involved the vertebral arch and spread into the canal (Fig. 3). After contrast administration, there was minimal enhancement of the pericyst capsule of the hydatid cyst. Only one hydatid cyst revealed small foci of peripheral calcifications (Fig. 4). Between the osseous part and hydatid cysts there was a clear cut, and the bone near the cyst was normal. The CT and MRI appearances of the vertebral hydatid cyst was typical for hydatid cyst in all cases.

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I. Tsitouridis and A. S. Dimitriadis: CT and MRI in vertebral hydatid disease

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Fig. 1 a, b. Axial postcontrast CT scans which show a hydatid cyst involving the vertebral arch and the left intervertebral foramen with cystic appearance and extension into the chest cavity

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Discussion Vertebral involvement by Echinococcus granulosus is a rare localization of hydatid disease. In most cases the disease affects the liver and lungs, but many other organs may be involved such as the bone. Osseous hydatidosis occurs in 0.28–3.1 % of hydatid disease cases and involvement of the vertebral column occurs in one third to one half of osseous cases [1–3]. The echinococcus embryo reaches the vertebra via the arterial circulation and lodgement occurs preferentially in the more highly vascularized zones, such as the vertebral centrum, but it is not unusual for laminae and pedicle to be the primary site of involvement. Hydropic degeneration of the echinococcus embryo occurs over many years without an adventitium membrane and reactive osteitis, and in this early stage the

Fig. 2. a Axial postcontrast CT scans at the level of L5 and sacrum which shows a lytic area at the posterior right parts of the vertebra extending into the spinal canal and the posterior fatty tissue. b Sagittal and c, d axial MR postgadolinium T1-weighted images which reveal the multilocular nature of the lesion, the extension into the spinal canal, and the posterior fatty tissue. The huge lobulated mass extends upwards to the level of L3 and posteriorly between the muscles and the fatty tissue, and the main part of the lesion is located at the right part of the sacrum. The cyst shows minimal enhancement at the pericyst

vertebrae maintain their shape. As the vesicles enlarge, the trabecular pattern of the bone may be destroyed and progressive extension of the cyst leads to invasion of the vertebral parts. When the cyst perforate the cortex the vesicles spill into adjacent paravertebral soft tissues or the intervertebral foramen, or into the spinal canal (extradural, intradural). Primary hydatid cyst of spinal cord and primary intradural and extradural cysts are very rare [4–7]. The slow growth of the parasite explains the late onset of symptoms. Extension of a vertebral hydatid cyst into the spinal canal results in compression symptoms of the spinal cord or the other elements of the canal [8–10]. The growth of hydatid cyst occurs along the intratrabecular spaces with the formation of diverticulated cysts that may form by exogenous vesiculation [3]. Enlargement and spread of hydatid cyst is achieved partially by

I. Tsitouridis and A. S. Dimitriadis: CT and MRI in vertebral hydatid disease

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Fig. 3 a, b. Sagittal MR T2-weighted images at the right side and postgadolinium T1-weighted image, which shows vertebral hydatid cysts which enlarge the intervertebral foramen secondary to the extension of the cysts through them, destroy the vertebral bodies of TH6 and TH7, and spread into the spinal canal. After intravenous gadolinium administration there is minimal peripheral enhancement of the pericyst Fig. 4. Axial CT scan which shows a hydatid cyst from the transverse process of the C3 vertebra. The cyst has water density and at the posterior wall there are some foci of calcifications

local pressure erosion of bone, while pressure on blood vessels within the bone may cause local necrosis. Our study reveals that vertebral involvement is more often a primary process without liver and lung involvement. The radiological approach of the vertebral hydatid disease includes plain radiographs, CT, and MRI. Plain radiographs show in the advance stage the bone destruction, but the radiological features are not pathognomonic [11]. The CT technique has the capability of providing more information about the anatomical localization of the vertebral hydatid disease [12, 13]. It provides a precise assessment of the osseous part of the lesion, the extension into the soft tissues, and the calcifications of the peripheral rim of the cyst, if they exist. The MRI technique is the method of choice because of its capability for revealing precise anatomic localization and extension of the vertebral hydatid disease. The MRI technique can clearly delineate the cerebrospinal fluid and the spinal cord without contrast medium being injected intrathecally. This is very useful to pick up some small daughter cysts after an osseous hydatid cyst rupture [14]. Although previous reports suggest that MRI seems to be less helpful than CT for showing minor osteolytic changes, we believe that MRI evaluation of small vertebral involvement is better than CT, especially on T1weighted images without intravenous gadolinium administration [13]. On MRI the signal from the cysts has very high intensity on T2-weighted images and low intensity on T1weighted images, but when there is a complication in the cyst, then the signal tends to be a little lower on T2weighted images and a little higher on T1-weighted images [15].

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4 Intravenous administration of gadolinium gives more information about the presence of infection in the cyst and the reaction of soft tissue where the cyst extends after its rupture. Previous reports suggest that CT and MRI are complementary methods in the evaluation of vertebral hydatid disease, but our experience shows that MRI is the superior method in the evaluation of the whole spectrum of vertebral hydatid disease (osseous part of the lesion, extension into the soft tissues, involvement of neural structures). We believe that MRI, with the capability of scanning at different planes, gives the appropriate information for the most suitable surgical approach. The evaluation of the stages of vertebral hydatid cyst development (simple viable cyst, hydatid cyst with daughter cysts, and end-stage calcified cyst) has some difficulties because of the exogenous vesiculation of the vertebral hydatid cyst, the absence of an adventitious layer or pseudocapsule, and the peculiar form of the bone as a host stroma. Regarding differential diagnosis based on imaging findings, on MR images the diagnosis should be highly suggestive because of the multicystic nature of the disease. When hydatid cyst is unilocular and complicated, then lytic metastatic tumors should be included in the differential diagnosis. Large exophytic parts of the lesion and condensed normal bone produced by the chronic presentation of hydatid cyst are the points which lead to the correct diagnosis. On CT images, bone neoplasms, particularly metastatic, should be considered in the differential diagnosis of hydatid cysts as either unilocular or mutiloculated.

References 1. Charles RW, Gowender S, Naidoo KS (1988) Echinococcal infection of the spine with neural involvement. Spine 13: 47–49 2. Argenson C, Griffet J, Lacour C et al. (1989) Vertebral hydatid cyst. Apropos of 2 cases. Rev Chir Orthop 75: 267–270 3. Rayport M, Wisoff H, Zaiman H (1964) Vertebral echinococcosis. Neurosurgery 21: 647–659 4. Ley A, Marti A (1970) Intramedullary hydatid cyst. J. Neurosurg 33: 457–459 5. Wani M, Taheri SA, Babu MC et al. (1989) Primary spinal extradural hydatid cyst. Neurosurgery 24: 631–632

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6. Akhan O, Dincer A, Saatci I et al. (1991) Spinal intradural hydatid cyst in a child. Br J Radiol 64: 465–466 7. Bavbek M, Inci S, Tahta K, Bertan V (1992) Primary multiple spinal extradural hydatid cysts of the literature: case report and review of the literature. Paraplegia 30: 517–519 8. Apt N, Fierro J, Calderon C et al. (1976) Vertebral hydatid disease. Clinical experience with 27 cases. J. Neurosurg 44: 72–76 9. Pamir N, Akalan N, Ozgen T, Erbengi A (1984) Spinal hydatid cysts. Surg Neurol 21: 53–57 10. Kaoutzanis M, Anagnostopoulos D, Apostolou A (1989) Hydatid disease affecting the vertebrae. Acta Neurochir Wien 98 (1–2): 60–65

Book review Heller, M., Fink, A. (eds.): Radiology of Trauma. Berlin Heidelberg New York: Springer 1997. 406 pp., 450 figs. in 843 separate illustrations, (ISBN 3-540-59324-1), hard cover, DM 298.00. This book represents a comprehensive and up-to-date overview of the current state of diagnostic imaging methods in trauma patients. Trauma has been a leading cause of death, morbidity and disability in developed countries, affecting the most productive section of the population. Adequate and favourable results depend greatly on early and exact diagnosis, which is the product of efficient cooperation and teamwork of several clinical specialities. Various radiological imaging modalities play a crucial role in elucidating all the traumatic sequelaes and differentiating between minor and lifethreatening injuries. The authors state the importance of achieving a diagnosis by means of simple conventional radiological procedures whenever this is reasonable, but also stress their limitations and drawbacks and the advantages of new diagnostic modalities. The indications for ultrasonography, spiral CT, 3D CT and MRI, in some acute trauma patients, are emphasized. Special attention has been paid to the quickest and most rational ways of achieving the correct diagnosis. Therefore, the authors provide numerous diagnostic algorithms appropriate for the most common posttraumatic events. The text is written concisely, in a readable style, and offers pertinent radiological as well as clinical information required by the busy radiologist working in an emergency department. Consequently, the number of references given at the end of each chapter is reduced and includes mainly the most important works published by internationally recognized experts in their fields. The clarity of explanations has been further improved by 450 figures of excellent quality and especially by 843 illustrations which cover all the practically important injuries to different anatomic regions. The book is well organized and divided into 14 chapters. After the first chapter, General Aspects of Trauma Radiology, which

11. Braithwaite P, Lees R (1981) Vertebral hydatid disease: Radiological assessment. Radiology 140: 763–766 12. Bouras A, Larde D, Mathieu D et al. (1984) The value of computed tomography in osseous hydatid disease (echinococcosis) Skeletal Radiol 12: 192–195 13. Ogut AE, Kanberoglu K, Altug A, Cokyuksel O (1992) CT and MRI in hydatid disease of cervical vertebrae. Neuroradiology 34: 430–432 14. Mikhael M, Ciric I, Tarkington J (1985) MR imaging in spinal echinococcosis. J Comput Assist Tomogr 9: 398–400 15. Sinner W von, Strake L, Clark D, Sharif H (1991) MR imaging in hydatid disease. AJR 157: 741–745

European Radiology provides many practical hints important for achieving the best possible imaging results under difficult circumstances of non-cooperating patients and life-threatening injuries, the subsequent chapters present the radiology of trauma according to their anatomic locations. Approximately half of the book is dedicated to serious trauma of the skull, brain and face, spine, neck, chest and abdominal trauma, which often presents as an emergency situation that requires immediate surgery. The remainder of the book deals with radiological diagnosis of skeletal trauma. These injuries, which are usually not life-threatening, represent the vast majority of emergency patients, and without proper radiological diagnosis and treatment may be the cause of life-long disability. The chapters are: The Shoulder Girdle, Elbow, Distal Forearm, Wrist and Hand, Pelvis, Hip and Proximal Femur, Knee Including Distal Femur, Proximal Tibia and Fibula, Ankle and Foot. At the end of the book a complete subject index is available. This excellent work is the result of cooperation between the editors and several contributors, who are all internationally recognised experts in the field of diagnostic imaging of trauma patients. It fulfils completely the declared goal “to provide an update of modern trauma diagnostics”. Moreover, the authors have succeeded in covering this important and extensive topic concisely in a book of appropriate volume and reasonable price. Therefore, “Radiology of Trauma” represents a successful continuation of the well-appreciated series “Medical Radiology: Diagnostic Imaging and Radiation Oncology”. The book has been primarily devoted to general radiologist and radiologists in training, but it could also be of great benefit to all the clinicians who are treating reauma patients. Although there are many books dealing with the same subject, “Radiology of Trauma” should be on the bookshelves of all trauma departments. V. Jevticˇ, Ljubljana