1 Introduction

Echinococcosis is a rare, severe zoonotic parasitic disease caused by infection with Echinococcus granulosus or Echinococcus multilocularis larvae.¹ Echinococcosis is distributed worldwide and occurs primarily in agricultural and pastoral areas, with a mortality rate between 0.9 and 3.6 %.² Echinococcosis most commonly occurs in the liver and lungs, which account for approximately 60–75 % and 30 % of all cases.³ Of the approximately 0.5–4% of all cases occurring in the bone, echinococcosis of the spine accounts for approximately half of cases. Lesions in the spinal canal and spinal cord are rare, and they mainly spread to the thoracic spinal cord when they are present there.⁴ Because intraspinal echinococcosis is extremely rare, the research reports are primarily limited to individual cases. Echinococcosis is characterized by an insidious onset, long incubation period, and a high disability rate. Therefore, most patients have severe lesions at the time of treatment, which can cause dysfunction and even death. With the increased development of tourism, the incidence of disease has been gradually increasing.

The current study analyzed the magnetic resonance imaging (MRI) manifestations and classification of 19 patients with intraspinal echinococcosis. The aims were to (1) explore the diagnostic value of MRI in spinal and intraspinal echinococcosis; (2) improve the early diagnosis of this disease; and (3) guide in clinical formulation of a reasonable treatment plan to improve the quality of life of patients.

2 Data and methods

3 Results

3.3

3.3 MRI findings

Enhanced MRI scan of six of the 19 patients revealed two cases (11 %) were located in the spinal cord. One case of intramedullary cystic echinococcosis showed multiple nodules at the lower end of the spinal cord and cauda equina, with beaded changes, equal or low-signal intensity on T1WI sequences, slightly high signal intensity on T2WI and fat-suppression sequences, and multiple high-signal vesicles in the center and along the periphery. The other case of intramedullary alveolar echinococcosis was located at approximately the level of the T11 vertebral body, showing a slightly thickened spinal cord, equal intensity nodular signaling on T1WI sequences, slightly lower intensity signaling on T2WI and fat-suppression sequences, and ring enhancement on an enhanced scan (Fig. 1). Nine cases (47 %) showed multiple oval-shaped long T1 and long T2 signal vesicles with a grape-like appearance, a low-signal intensity cyst wall at the edge, spinal cord compression, and subarachnoid space narrowing (Fig. 2). Several showed extramedullary subdural lesions with slightly long T1 and long T2 signals, scattered long T2 signal vesicles surrounding them, and low-signal cyst walls. Nine cases (47 %) of extradural epidural lesions showed slightly low signal intensity on T1WI sequences, slightly high-signal intensity on T2WI and fat-suppression sequences, multiple high-signal vesicles in the center and periphery, compression of the dural sac, and narrowing of the subarachnoid space (Fig. 3). Thirteen cases (68 %) simultaneously involved the adjacent vertebral body, appendages, or surrounding soft tissue, revealing vertebral expansion and osteolytic bone destruction. Multiple low or equal intensity signals on T1WI sequences, clustered or diffuse “grape-like” high-intensity signals, small vesicle-like signals on T2WI sequences, and fat suppression were observed in the vertebral body or soft tissue (Fig. 4).

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Fig. 1 Intramedullary alveolar echinococcosis was located at approximately the level of the T11 vertebral body and showed slight thickening of the spinal cord with equal-intensity nodular T1WI signaling and slightly lower-intensity T2WI and fat-suppression sequence signaling, and enhanced scanning showing annular enhancement. A–D: T1WI, T2WI, T2-STIR, and T1-enhanced sequences.

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Fig. 2 A lesion involved in the extramedullary subdural space showed multiple oval-shaped long T1 and long T2 signal vesicles of a grape-like appearance, low signal intensity cyst walls with low edges, spinal cord compression, and subarachnoid space narrowing. A–D: T1WI, T2WI, T2-STIR, and T2WI axial sequences.

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Fig. 3 Extramedullary epidural lesions showed slightly low signal intensity on T1WI sequences, slightly high signal intensity on T2WI and fat-suppression sequences, multiple high signal small vesicles in the center and periphery, compression of dural sac, and narrowing of subarachnoid space. A–D: T1WI, T2WI, T2-STIR, and T2 axial sequences.

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Fig. 4 Involvement of the vertebral body and paravertebral soft tissue manifested as vertebral expansion and osteolytic bone destruction. Multiple T1WI low or equal intensity signals were observed in the vertebral body or soft tissue, and T2WI and fat-suppression sequences showed clustered or diffuse small, high-intensity, “grape-shaped,” vesicle-like signals. A–E: T1WI, T2WI, T2-STIR, coronal T2WI, and axial T2WI sequences.

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4 Discussion

Echinococcosis is a rare but malignant growth caused by the echinococcosis tapeworm. A neglected tropical disease, this zoonotic infection has been reported on all continents except Antarctica but is more common in warmer regions, such as South America, the Mediterranean, the Middle East, New Zealand, southern and central Russia, Australia, China, and northern and eastern Africa.⁶ Exposure to echinococcosis eggs may be affected by occupational and behavioral factors,⁷ and most patients have a history of living in agricultural and pastoral areas. Echinococcosis infection is more common in the liver and lungs because these organs capture most larvae. Spinal echinococcosis is the result of echinococcosis eggs hatching into hookworms in the human intestines and invading mesenteric blood vessels before reaching the liver through the portal system and then, rarely, reaching the vertebral body through the blood circulation.⁸

A rare disease, with an incidence of less than 1 %, spinal echinococcosis mostly results from the invasion of adjacent vertebral echinococcosis. The embryo of echinococcosis usually stays in the spinal blood vessels in the vertebral body, where it produces multiple microvesicles before penetrating the bone wall. After the cyst enters the spinal canal, it compresses the spinal cord and the spinal canal root while the dura remains intact. In a very small number of primary cases, a small amount of cerebrospinal fluid spreads from the cerebral echinococcosis. Neumayr et al.^9,10 found that the average age of onset of spinal echinococcosis was 35 (range 3–77) years for all patients, 35 (range 3–76) years for male patients, and 36 (4–77) years for female patients and that the prevalence was higher in males than females. In a large case series, the average age of onset ranged from 30 to 36 years old. In this study, the age of onset of patients with intraspinal echinococcosis ranged from 28 to 65 years, with a median age of 39 years and a male-to-female ratio of 9:10. These findings may be due to the small sample size examined in this study and the bias arising from the inclusion of only patients with echinococcosis involving the spinal canal.

The clinical manifestations of spinal echinococcosis depend on the degree of vertebral involvement and stage of disease. The initial stage of primary infection is always occult, asymptomatic, non-specific, and related to the location and size of the lesion. Small cysts may be asymptomatic for many years. When the size of the lesion increases, symptoms may occur. In this study, 18 patients (95 %) had chest and back pain, and four patients (21 %) had symptoms in the lower limbs. At the same time, the symptoms of spinal echinococcosis also depend on the degree of compression of the spinal cord.¹¹ Nervous system complications arise from compression myelopathy or neuropathy caused by intradural and epidural disease components.¹² These clinical features may be non-specific and vary with the location of the lesion. The onset of symptoms can vary from acute to long term, which increases the difficulty of diagnosis. Other common symptoms include back pain, paralysis, radiculopathy, sensory disturbances, and sphincter involvement.¹³

MRI is currently the best examination method for the diagnosis of intraspinal echinococcosis because of its high soft-tissue resolution and clear spinal-cord imaging, which can show more subtle structures and microvesicles. The specific manifestations are cystic lesions with clear boundaries, low-intensity T1WI signals, and high-intensity T2WI signals. T2WI sequences can show the cyst wall surrounding the homogeneous high-signal cyst contents, which may be thin and regular, and the signal may be lower than its content. Echinococcosis is characterized by a cyst wall with significantly low T1WI and T2WI signaling intensity that may be slightly enhanced after injection of gadolinium, reflecting the vascular distribution of the peripheral cells.¹⁴ In this study, two patients (11 %) showed equal or slightly shortened T2WI signals surrounding multiple small vesicles. Sixteen cases (84 %) showed long T1WI and long T2WI signals surrounding vesicles of different sizes with a grape-like appearance, with low-intensity signals around the edge of the cyst wall, findings consistent with the literature. One case (5 %) of intramedullary alveolar echinococcosis was characterized by a slightly thickened spinal cord, equal-intensity nodular T1WI signaling, slightly lower-signal intensity signaling on T2WI and fat-suppression sequences, and ring enhancement on an enhanced scan.

In cases in endemic countries, which are typically characterized by a densely calcified edge around the lesion, the daughter cyst shows a watery signal, the mother cyst shows a muscle-like signal in in T1WI sequences, and the mother and daughter cysts show rose or wheel-like signals in T2WI sequences,¹⁴ MRI features that may indicate infection. Song¹⁵ described many typical and atypical signs, such as focal edema, uneven enhancement, diversity or separation and calcification, and various unusual manifestations caused by cyst rupture or infection. In this study, 10 cases (53 %) involved the thoracic spine. Consistent with the literature,^16,17 extramedullary subdural and extramedullary epidural spaces were observed in nine (Type II) (47 %) and nine (Type III) (47 %) cases, respectively. These findings may be attributed to the fact that the thoracic spine is considered a cavernous vertebral body with strong local vascularization and abundant blood circulation.¹⁸ Moreover, 69 % of cases involved adjacent vertebral bodies, accessories, and surrounding soft tissues simultaneously. Intraspinal echinococcosis is often accompanied by adjacent vertebral bodies and soft tissue involvement, an important feature of the disease because the spinal canal itself penetrates the dura mater and invades the vertebral body.

The differential diagnosis of intraspinal echinococcosis includes other intraspinal lesions. Intramedullary lesions include hematoma, arachnoid cyst, astrocytoma, and ependymoma; extramedullary subdural lesions include neurogenic tumors and meningioma; and extramedullary epidural lesions include metastases and lymphoma.

This study had several limitations that should be considered when reviewing the findings. The overall incidence of spinal echinococcosis is rare and lower than that of other tissues. The number of patients included in this study was small, and the recording of the results may have errors. The study was long, and only a few patients underwent MRI enhanced scan at the same time, which may have placed certain limitations on analyzing the MRI characteristics of the disease.

In conclusion, although intraspinal echinococcosis is extremely rare, it may cause significant lower back pain, weakness, and numbness in patients living in endemic areas. The disease should be considered in patients with obvious MRI features with a history of living in agricultural and pastoral areas or with a history of echinococcosis infection in other tissues. At the same time, cystic or pseudocystic intraspinal lesions of different etiologies may show overlapping clinical and imaging features. When considering the disease, the specific location, whether extramedullary epidural, extramedullary dural, or intramedullary, should first be considered, and the diagnosis should then be confirmed by serum immunological examination.

Potential conflicts of interest

All authors: no reported conflicts of interest.

Availability of data and materials

The data sets cannot be made publicly available, and restrictions apply to the availability of these data. Data can be requested from the authors and require permission from Xinjiang Medical University affiliated First Hospital.

Ethics approval and consent to participate

This study was conducted in accordance with the principles of the Helsinki Declaration. It was reviewed and approved by the First Affiliated Hospital of Xinjiang Medical University research ethics committee for exemptions and exemptions from written informed consent requirements.

Consent to publish

All authors agreed to be published in this journal.

Author contributions

H. G. and W.L.conceived the idea. Y.C. and H.G.wrote the main manuscript text, and X.H. prepared Figs. 1–4. Y.C. and X.H. collected the data.Y.C. and X.H. performed the literature search. All authors reviewed the manuscript. All authors approved the final version for submission.