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La radiologia medica https://doi.org/10.1007/s11547-019-00988-z
MAGNETIC RESONANCE IMAGING
Differentiation between intraspinal schwannoma and meningioma by MR characteristics and clinic features
Xiaodong Zhai1 · Ming Zhou1 · Hongwei Chen1 · Qunfeng Tang1 · Zhimin Cui1 · Yong Yao2 · Qihua Yin1
Received: 24 August 2018 / Accepted: 7 January 2019 © Italian Society of Medical Radiology 2019
AbstractObjectives To retrospectively review the MRI characteristics and clinic features and evaluate the effectiveness of MR imag-ing in differentiating intraspinal schwannomas and meningiomas, with the excised histopathologic findings as the reference standard.Materials and methods One hundred and four schwannomas (M/F, 57:47) and 53 meningiomas (M/F, 13:40) underwent MR examinations before surgical treatment. Simple clinic data and imaging findings were considered:(a) location (craniocaudal and axial), (b) size, (c) morphology, (d) dural contact, (e) signal characteristics, (f) enhancement degree and patterns. The usefulness of the algorithm for differential diagnosis was examined between the two tumors.Results Interobserver agreement was good (κ = 0.7–0.9). Ten cases meningiomas demonstrated multiple lesions. There was a female predominance in the meningiomas (P < 0.001). Meningiomas predominantly were located in the ventral or anterolateral areas of thoracic regions, while schwannomas in the posterolateral areas of the thoracic and the lumbar regions (P < 0.001). Mean size of the lesions was 1.47 ± 0.36 cm for meningioma, and 2.02 ± 1.13 cm for schwannoma (P < 0.001). A dumbbell shape with intervertebral foramen widening could detect schwannomas, while the “dural tail sign” did menin-giomas (P < 0.001). Hypointense and miscellaneous signal implied meningioma on T1WIs (P < 0.001). Isointense was more frequently observed in the meningiomas, while the fluid signal intensity and miscellaneous signal in the schwannomas on T2WIs (P < 0.001). Schwannomas usually manifested rim enhancement, while meningiomas diffuse enhancement (P = 0.005). There were six variables including the logistic equation (age, size, dural tail sign, morphology, T2WI, and axial location). The accuracy of the algorithm in diagnosis of schwannomas was 87.1%.Conclusions Combination of clinic data and MRI performs significantly for differentiating between intraspinal meningiomas and schwannomas.
Keywords Spinal meningioma · Schwannoma · Magnetic resonance imaging
Introduction
Schwannoma and meningioma are the two most frequent spi-nal intradural extramedullary tumors (comprising 55%) [1]. Clinicians and radiologists have made attempts to differenti-ate the two lesions based on computed tomography (CT) and magnetic resonance imaging (MRI) appearances. However, this may be formidable in a host of cases due to significant overlap in features on conventional imaging and in the clini-cal settings [2]. Thus, differentiation of spinal meningiomas and schwannomas is not always reliable and remains a mat-ter of debate. Preoperative differential diagnosis between the two is critical due to the operative approach and prognosis differences. The surgical treatment of schwannomas requires incision of both the dura mater and arachnoid membrane,
Yong Yao and Qihua Yin have contributed equally to this work.
* Yong Yao [email protected]
* Qihua Yin [email protected]
Xiaodong Zhai [email protected]
1 Department of Radiology, The Affiliated Wuxi People’s Hospital of Nanjing Medical University, No.299, Qingyang Road, Wuxi 214000, Jiangsu Province, China
2 Department of Ophthalmology, The Affiliated Wuxi People’s Hospital of Nanjing Medical University, No.299, Qingyang Road, Wuxi 214000, Jiangsu Province, China
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because the tumors reside in the subarachnoid space. To pre-vent postoperative leakage of cerebrospinal fluid (CSF), the dura mater and arachnoid membrane are sutured to produce a watertight dural closure. Meanwhile, meningiomas reside intradurally in the extra-arachnoid space. The attachment site of the meningioma to the dura mater must be resected with the tumor to remove any residual tumor cells; thus, preservation of the arachnoid membrane helps prevent post-operative CSF leakage. Meningiomas exhibit a higher rate of recurrence than schwannomas. As preventive methods such as coagulation or total durotomy of the attachment site are essential in patients with meningioma [3–6]. To solve this issue, we conducted this retrospective study to develop the usefulness of MR imaging for the differential diagnosis of these two entities.
Materials and methods
Population data
This retrospective study was approved by our institutional review board, and the requirement for informed consent was waived. One hundred and eighty-four consecutive patients were reviewed between January 2009 and December 2017 who had undergone MRI prior to tumor resection at our hospital. The following inclusion criteria were: (a) pathol-ogy-proven meningiomas or schwannomas, (b) patients with multiparametric MR imaging including T1WI, T2WI, and enhanced T1WI sequences, and (c) patients with surgical resection.
Of these, 27 patients were excluded for the following reasons: (a) patient with operation before (n = 4), (b) neu-rofibromatosis (n = 5), (c) unsatisfactory imaging quality for review (n = 6), (d) main part of lesion-located para-vertebral region (n = 4), or (e) without enhancement MR images (n = 8). Therefore, a final cohort of 157 patients was included.
We reviewed each case with respect to age, gender, the nature of preoperative symptoms, duration of the symptoms, location of the tumor and MRI findings.
Imaging data
All MR examinations in all 157 patients were performed on 1.5-Tesla MR scanner (65 cases, Magnetom Aera; Siemens Healthcare, Erlangen, Germany) or 3.0-Tesla MR scanner (92 cases, Siemens Magnetom Trio Tim, Erlangen, Ger-many), and surface coils were used for all patients.
Including T1WI spin-echo (SE) sagittal (for 1.5T, TR/TE = 550/11 ms, NEX = 4, for 3.0T TR/TE = 500/9.5 ms, NEX = 4), and fast spin-echo (FSE) T2-weighted sequences (TR/TE = 3000/500 ms for 1.5T; TR/TE = 2500/100 ms for
3.0T) sequences T2WI axial (for 1.5T, TR/TE = 500/12 ms, NEX = 4; for 3.0T, TR/TE = 470/11 ms, NEX = 4), and fol-lowed by enhanced fat-suppressed T1WI in the axial plane, the sagittal and the coronal plane. Matrix used for examina-tion ranged from 128 × 256 to 256 × 512 pixels. The slice thickness was 3 mm with 0.3 mm interslice gap for the sagit-tal and coronal image and 4 mm with 1 mm interslice gap for the axial image. The enhanced images were obtained using intravenous paramagnetic contrast medium (Gadopentetate dimeglumine) injection at a dose of 0.1 mmol/kg.
All images were transferred to Syngo via 102,230 work-stations and reviewed retrospectively by two radiologists (10 and 8 years of experience, respectively, with spine MR imaging). Both of them were blinded to age, gender, clinical history, symptoms and histopathologic results at the time of interpretation.
Following items were evaluated on MR images
It’s location
(a) Craniocaudal: cervical region, cervicothoracic region, thoracic region, thoracolumbar region, lumbar region, lum-bosacral region or sacral region; and (b) Axial location: anterolateral, posterolateral or lateral, and ventral (midline anterior) or dorsal (midline posterior).
Size
As the average of long and short axes more accurately reflects three-dimensional tumor volume [7]. The size of lesion used the average of long- and short-axis diameters on the same slice, whichever plane reveals the greatest dimen-sions. The greatest diameter of each tumor was obtained on the contrast-enhanced images.
Morphologic characteristics
(1) Oval or round shape (mainly depending on sagittal/coro-nal images), (2) Dumbbell type, (3) Intervertebral foramen widening, (4) the Ginkgo leaf sign.
The ginkgo leaf sign: The shape of the deformed cord and the streak resembled a ginkgo leaf on contrast-enhanced axial MR images [8].
Dural contact
The “dural tail sign” was considered according to the follow-ing criteria [9]: (1) the tail should be identified at least on two successive sections through the tumor, (2) the tail should taper smoothly away from the tumor, and (3) the tail has an
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enhancement greater than that of the tumor itself, with bone signal abnormalities occasionally.
Signal characteristics on T1WI (precontrast) and T2WI
The signal intensity of the lesions was compared with that of the spinal cord. The lesion was identified as homogeneity or heterogeneity, and the signal intensity was classified by the main part (more than 80%). Signal intensity was categorized into four groups on T1WI (precontrast) and five groups on T2WI. (1) Hypointense was lower than spinal cord, not equal to CSF, (2) Isointense was equal to spinal cord, (3) Hyper-intense was higher than spinal cord and (4) Miscellaneous signal was formed by of different signs but not classified as any of the aforementioned, and (5) Cystic degeneration (for T2WI) as indicated by signal intensity equal to that of the cerebrospinal fluid, exhibiting low intensity on T1WI and high intensity on T2WI.
Enhancement degree and patterns on T1WI
1. Enhancement degree was classified as: (a) Marked enhancement was more than vertebral body signal as high as that of the subcutaneous fat (regardless of the fat’s enhancement pattern), (b) Moderate enhancement was equal to (comparable) to the vertebral body signal, and (c) None when the was signal lower than the verte-bral body.
2. Enhancement pattern was classified as: (a) Diffuse, when the appearance of most of lesion was homogene-ous (> 80%); (b) Rim, when it was peripheral or ring-enhancing (with or without septal enhancement), (c) Focal, when the heterogeneous enhancing part inside the lesions (< 25%); and (d) as None (i.e., no enhance-ment).
Histopathologic analysis
The diagnosis of meningioma and schwannoma was based on the histopathologic studies by macroscopical observation, subsequently with electron microscopy as well as immuno-histochemical examination of the tissue excised by surgery.
Statistics
Differences characteristics in quantitative were analyzed using an independent sample t test, while the qualitative characteristics were analyzed using Chi-square tests. And a multivariate logistic regression analysis was performed to assess which factors affected the diagnosis results between schwannomas and meningiomas based on the performance of MR image findings and simple clinic data. Diagnostic
parameters—sensitivity (SE), specificity (SP), positive pre-dictive value (PPV) and negative predictive value (NPV)—were calculated on a lesion and a patient basis for MR imaging.
Interobserver agreement analysis with k statistic was performed to determine consistency between the two radi-ologists for detection of tumor for the different MR imag-ing findings. The k values were interpreted as follows: 0.00–0.20, slight agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, substantial agreement; and 0.81–1.00, almost perfect agreement (28). All statistical analyses were performed using SPSS version 22.0 for Windows (IBM, Armonk, NY, USA). A P value of < 0.05 was considered statistically significant.
Results
Their clinical symptoms were nonspecific. Most of the patients had progressive transverse spinal cord lesions, such as progressive paraparesis, nerve palsy, shoulder and back pain, sciatica, impotence, and bowel dysfunctions. Table 1 demonstrates a summary of the clinic manifestation and MR characteristics of the schwannomas and meningiomas.
Patient characteristics
Of the 157 cases of spinal intradural extramedullary tumors, 53 cases were confirmed to be meningiomas (male vs. female, 13:40) with an age ranging from 30 to 86 years (61.4 ± 13.2, mean ± SD). Among the meningioma group, there was a predominance in the female group (40 cases, 75.5%), and there were 43 (81.1%) patients with the age of 61–87 years. There was no meningioma with the age of less than 31 years old.
And 104 cases were confirmed to be schwannomas (male vs. female, 57:47) with an age ranging from 20 to 79 years (51.1 ± 15.2, mean ± SD). There were only 12 (11.5%) patients with the age of 20–30 years old, and most of the schwannomas were found with the age of 31–70 years old (83 cases, 79.8%). There was no significant predisposed fac-tor based on the gender (Table 1).
There was a significant difference in the proportion of women between the two groups (χ2 = 13.028, P = 0.000), while there was no significant difference in mean age (F = 1.941, P = 0.166).
MRI findings of meningioma and schwannoma
Tumor location
In the axial plane, 20 (33.7%) meningiomas were ven-tral or anterolateral (5 cases, 9.4%; 15 cases, 28.3%,
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right-anterolateral/left-anterolateral, 4:1), 13 (24.5%) meningiomas were dorsal or posterolateral (3 cases, 5.7%; 10 cases, 18.8%, right-posterolateral/left-posterolateral, 4:1), and 20 (37.7%) meningiomas were lateral (right/left, 3:1). Concerning schwannomas, 9 cases (8.6%) were ventral or anterolateral (one case, 0.96%; 8 cases, 7.6%, right-anterolateral/left-anterolateral, 3:1), 42 cases (40.4%, right-posterolateral/left-posterolateral, 4:3) were postero-lateral, while there was no case identified in the dorsal region, and 43 (41.4%) schwannomas were lateral (right/left, 22:21). However, due to multiple lesions in intraspinal canal, 10 (9.6%) cases were not evaluated (Fig. 1).
Statistical analysis manifested significant difference between the two groups (χ2 = 47.33, P < 0.001). Meningi-omas often occurred in the ventral or anterolateral, while schwannomas in the posterolateral region.
Craniocaudal distribution evaluations were demonstrated as follows: 6 (11.3%) meningiomas and 20 (19.2%) schwan-nomas were in the cervical region, 46 (86.8%) meningi-omas and 31 (29.8%) schwannomas in the thoracic region, 1 (1.9%) meningioma and 28 (26.9%) schwannomas in the lumbar region, and 2 (1.9%) schwannomas in the sacral region, but no meningioma in the sacral region (Fig. 1). For the schwannomas, there were 13 (12.5%) cases in the ver-tebral junction regions (cervical-thoracic, thoracic-lumbar and lumbosacral: 3, 6 and 4 cases, respectively), and mul-tiple schwannomas (10 cases, 9.6%) occurred in anywhere of intraspinal canal (cervical, thoracic, thoracic-lumbar and lumbosacral: 5, 3, 1 and 1 cases, respectively), of which features were not manifested in the meningiomas group.
Statistical analysis demonstrated difference between the two groups: Meningiomas seldom occurred in the vertebral junction regions. Meningiomas were predominantly located
Table 1 Patients clinical characteristics
Meningioma Schwannoma P(n = 53, %) (n = 104, %)
Gender Male 13 (24.5%) 57 (54.8%) < 0.01Female 40 (75.5%) 47 (45.2%)
Age (years) Mean ± SD (range) 61.4 ± 13.2 (30–86) 51.1 ± 15.2 (20–79) = 0.166≤ 20 0 (%) 1 (%) /21–30 0 (%) 11 (%) /31–40 4 (%) 15 (%) /41–50 6 (%) 19 (%) /51–60 16 (%) 27 (%) /61–70 13 (%) 21 (%) /≥ 71 14 (%) 10 (%) /
Size Mean ± SD 1.47 ± 0.36 2.02 ± 1.13 <0.01
Fig. 1 a The craniocaudal distribution of tumors. Meningiomas were predominantly located thoracic regions (46, 86.8%), while schwan-nomas in the thoracic regions (31, 29.8%), the lumbar regions (28, 26.9%) and cervical regions (20, 19.2%). Tumors in the vertebral junction regions and multiple lesions were only demonstrated in the
schwannoma group. b The axial plane distribution of tumors. Menin-giomas were most in the ventral or anterolateral regions (20, 33.7%) and the lateral regions (20, 37.7%), while schwannomas in the poste-rolateral regions (42, 40.4%) and the lateral region (43, 41.4%). Mul-tiple lesions were only manifested in the schwannoma group
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thoracic regions, while schwannomas in the thoracic and the lumbar regions (χ2 = 42.93, P < 0.001).
Size of tumor
Mean size of the lesions was 1.47 ± 0.36 cm (range, 0.75–3.0 cm) for meningiomas, and 2.02 ± 1.13 cm (range, 0.70–8.45 cm) for schwannomas. When it came to the mul-tiple lesions, the maximum lesion was analyzed. (Table 1) Independent test demonstrated that there was significantly different between two groups (t = −4.52, P = 0.000).
Although the size of meningiomas was more than 1.88 cm in only five patients, the schwannomas was in 44 patients. And the size (> 1.88 cm) was used for the unique reference value of schwannomas, and PPV, NPV, SE, SP and accuracy were 90.6%, 44.4%, 42.3%, 90.6% and 58.6%, respectively (Table 2).
Morphologic characteristics
Almost all meningiomas manifested oval or round shape, except that three cases demonstrated the type of growth along the intervertebral foramen with slight intervertebral foramen extension. Oval or round shape was observed in 63 cases of schwannomas, and a dumbbell shape with interver-tebral foramen widening was manifested in 31 cases (multi-ple lesions not involved). The proportion of dumbbell-type lesions was significantly higher in the schwannomas group (Fig. 2a). Of 10 multiple cases of the schwannomas group, one lesion presented a dumbbell shape with intervertebral foramen widening, and the others presented oval or round shape (Fig. 3).
The morphology of the tumors was statistically differ-ent between two groups (χ2 = 33.48, P < 0.001). Overall, the sign of a dumbbell shape with intervertebral foramen widening was able to detect schwannomas with SE, SP,
Table 2 Accuracy of MRI findings for differential diagnosis between two entities
IFW intervertebral foramen widening, SE sensitivity, SP sensibility, PPV positive predictive value, NPV negative predictive value
Tumor SE (%) SP (%) PPV (%) NPV (%) Accuracy (%)
Size of tumor (> 1.88 cm) Schwannoma 42.3 90.6 90.6 44.4 58.6Dumbbell shape with IFW Schwannoma 33.0 94.3 91.2 44.2 55.1Dural tail sign Meningioma 60.4 93.6 84.2 80.7 81.6Hypointensity (T1WI) Schwannoma 53.8 94.3 94.9 51.0 67.5Miscellaneous signal (T1WI) Schwannoma 5.8 100 100 35.1 37.5Fluid signal intensity (T2WI) Schwannoma 30.0 87.7 24.2 81.6 48.4Miscellaneous signal (T2WI) Schwannoma 18.3 100 100 38.4 45.9Rim enhancement Schwannoma 32.7 86.8 82.9 39.6 51.0Diffuse enhancement Meningioma 86.8 37.5 41.4 84.8 54.1Multivariate logistic regression Schwannoma 92.6 77.4 87.9 85.4 87.1
Fig. 2 a The morphologic characteristics of tumors. IFW = interver-tebral foramen widening. The morphology of the tumor was statisti-cally different between the two groups (χ2 = 33.48, P < 0.001). Menin-giomas and schwannomas shared the imaging features of solid, round or oval, well-circumscribed lesions (meningioma vs. schwannoma, 50 vs. 63). A dumbbell shape with intervertebral foramen widening
almost occurred in the schwannoma group (meningioma vs. schwan-noma, 3 vs. 31). b The dural tail of sign of tumor. Thirty-two (60.4%) meningiomas demonstrated the “dural tail sign,” and only 6 (6.8%) schwannomas did the “dural tail sign” on contrast-enhanced T1WI. The “dural tail sign” was highly significant difference between the two groups (χ2 = 51.55, P < 0.001)
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PPV NPV and accuracy of 33.0%, 94.3%, 91.2%, 44.2% and 55.1%, respectively. (Table 2) Only 2 (2/53, 3.8%) of meningiomas were positive for the “ginkgo leaf sign,” and the sign was negative in the schwannoma group (Fig. 3).
Dural contact
Thirty-two meningiomas (32/53, 60.4%) demonstrated a “dural tail sign” on contrast-enhanced T1WIs. Only six schwannomas (6/88, 6.8%, multiple lesions not involved) presented the “dural tail sign.” The “dural tail sign” was highly significant between two groups (χ2 = 51.55, P < 0.001) (Figs. 2b, 3). The “dural tail sign” may detect meningioma with SE, SP, PPV, NPV and accuracy of 60.40%, 93.6%, 84.2%, 80.7% and 81.6%, respectively (Table 2). There was no the “dural tail sign” in multiple schwannomas in our work.
Signal intensity on T1WI (precontrast) and T2WI
On precontrast T1WIs, 3 (5.7%) meningiomas were hypoin-tense, and 50 (94.3%) cases were isointense (hetero-/homog-enous, 15/35). Of the schwannomas (multiple lesions were involved in, the maximum lesion was analyzed), 56 (53.8%) cases were hypointense (hetero-/homogenous, 36/20), 40 (38.5%) cases were homogenous isointense on precontrast T1WIs, 2 cases hyperintense and 6 cases miscellaneous sig-nal were only manifested in the schwannomas group (1.9%, 5.8%, respectively).
Of the meningiomas on T2WIs, 2 cases (3.8%) demon-strated hypointense signal, 33 cases (62.3%) demonstrated isointense signal (hetero-/homogenous, 8/25), 11 cases (20.8%) manifested hyperintense signal, and 7 cases (13.2%) manifested fluid signal intensity (cyst degeneration). In contrast to meningiomas, 23 (22.1%) schwannomas dem-onstrated isointense signal on T2WIs (hetero-/homogenous,
Fig. 3 The morphology and dural characteristics were shown on T1WI enhancement. a The dumbbell shape with interver-tebral foramen widening (white arrowhead). b The “ginkgo leaf sign” (white arrowhead). c The “dural tail sign” (white arrow). d The oval or round (white arrow)
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12/11), 31 (29.8%) schwannomas demonstrated hyperintense signal (hetero-/homogenous, 18/13), and 31 schwannomas (29.8%) demonstrated fluid signal intensity (cyst degenera-tion). Miscellaneous signal was observed in 19 schwanno-mas (18.3%) (Figs. 4a, b and 5).
There was statistical difference in signal intensity (hypointense and miscellaneous signal) on precontrast T1WIs between meningiomas and schwannomas (χ2 = 44.89, P < 0.001), which could differentiate schwannomas from meningiomas with SE, SP, PPV, NPV and accuracy of 53.8%, 4.3%, 94.9%, 51.0% and 67.5%, 5.8%, 100%, 100%, 35.1% and 37.5%, respectively. (Table 2) And on T2WIs, isointense was more frequently observed in the meningi-oma group, while the fluid signal intensity (cyst degenera-tion) and miscellaneous signal were highly significant in the schwannoma group (χ2 = 35.31, P < 0.001), which could detect schwannoma with SE, SP, PPV and NPV of 30.0%, 87.7%, 24.2% 81.6% and 48.4%, 18.3%, 100%, 100% 38.4% and 45.9%, respectively. (Table 2) Signal heterogeneity was not statistically different on precontrast T1WIs between men-ingiomas and schwannomas (χ2 = 1.06, P = 0.302), but on T2WIs (χ2 = 37.28, P < 0.001)
Degree of enhancement and enhancement pattern
Forty-six (86.8%) meningiomas demonstrated diffuse enhancement and 7 (13.2%) meningiomas demonstrated rim enhancement, of which moderate and marked enhance-ment were manifested on contrast-enhanced MR images (moderate/marked 2/44, 1/6, respectively). Among diffuse
enhancement, 10 cases demonstrated heterogeneity and 36 cases manifested homogeneity (Fig. 4c).
In the schwannomas group, multiple lesions were involved in, the maximum lesion was analyzed. Sixty-five (62.5%) schwannomas manifested diffuse enhance-ment. Thirty-four (32.7%) schwannomas demonstrated rim enhancement, and 5 (4.8%) schwannomas did focal enhance-ment, of which moderate and marked enhancement were as follows: diffuse: 0/65, rim: 1/33, focal: 1/4, respectively. Forty-one cases manifested heterogeneous diffuse enhance-ment, and 24 cases did homogeneous diffuse enhancement. There was one rim marked case with focal mural nodule enhancement, but there was not nonenhancement lesion on contrast-enhanced T1WIs in both groups (Fig. 6).
There was no significant statistical difference in degree of enhancement between schwannomas and meningiomas in our examine (χ2 = 1.58, P = 0.336), but to enhancement pattern on contrast-enhanced T1WIs, schwannomas usually demonstrated rim enhancement while meningiomas mostly did diffuse enhancement (χ2 = 10.58, P = 0.005) which could detect schwannoma and meningioma with SE, SP, PPV NPV and accuracy of 32.7%, 86.8%, 82.9% 39.6% and 51.0%, 86.8%, 37.5%, 41.4%, 84.8% and 54.1%, respectively. (Table 2)
Multivariate logistic regression
Imaging findings with a P value < 0.05 at multivariate analy-sis were assessed by binary logistic regression as follows. There were six variables including the logistic equation (age, size, dural tail sign, morphology, T2WI [P = 0.08–0.03],
Fig. 4 a The signal characteristics of T1WI. Meningiomas were almost hypointense (50, 94.3%), while schwannomas (multiple lesions involved, the maximum lesion was analyzed), 56 (53.8%) cases were hypointense, 40 (38.5%) cases homogenous isointense, 2 cases hyperintense and 6 cases miscellaneous signal. b The signal characteristics of T2WI. Meningiomas (33, 62.3%) mainly demon-strated isointense signal, hypointense, hyperintense and fluid sig-nal intensity were 2 (3.8%), 11 (20.8%) and 7 (13.2%), respectively. There was no hypointense in the schwannoma group. Isointense, hyperintense, fluid signal intensity and miscellaneous signal were
23 (22.1%), 31 (29.8%) 31 (29.8%) and 19 (18.3%), respectively. c The degree and the pattern of enhancement. Fifty meningiomas demonstrated marked enhancement and 3 cases moderate, while 102 schwannomas did marked enhancement and 2 cases did moder-ate enhancement. Forty-six (86.8%) meningiomas manifested diffuse enhancement, and 7 (13.2%) meningiomas rim enhancement, while 65 (62.5%) schwannomas did diffuse enhancement, 34 (32.7%) rim enhancement, and 5 (4.8%) focal enhancement. Schwannomas usu-ally demonstrated rim enhancement, while meningiomas did diffuse enhancement (χ2 = 10.58, p = 0.005)
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and axial location [P = 0.055], χ2 = 100.66, P < 0.005). The accuracy of the algorithm in diagnosis of schwannomas was 87.1% and was with SE, SP, PPV and NPV of 92.6%, 77.4%, 87.9% and 85.4%, respectively (Table 2).
Interobserver reliability
There was substantial to excellent agreement for lesion detection with the MR imaging findings. (weighted k, k = 0.82 for the size of tumor, k = 0.90/0.7 for occurrence of craniocaudal location/axial location, k = 0.88 for the mor-phology, k = 0.83 for dural tail sign, k = 0.71/0.72 for T2WI/T1WI, and k = 0.85/0.80 for enhancement degree/pattern).
Discussion
Intradural spinal tumors can be divided into extramedullary and intramedullary tumors. The four most common intra-dural spinal tumors are the following: schwannoma (30%), which is the most common intradural extramedullary spi-nal tumor, occurring at a rate of approximately 0.3–0.4 per
100,000 persons per year. Meningioma (25%), which is the second most common intradural extramedullary spinal tumor, occurring in approximately 0.32 per 100,000 persons per year. Intradural intramedullary of which concerning 90% is glial tumors; ependymoma (60%) is the most common spinal cord tumor in adults, and astrocytoma (30%) is the second most common spinal cord tumor in adults [1, 10].
MRI is considered the best preoperative imaging tech-nique to diagnose spinal tumors. In this work, we aimed to investigate the usefulness of MRI findings to aid in diagnosis and differentiation. Studying the statistical weight of these modalities on basis of multivariate logistic regression, six statistically significant findings (age, size, dural tail sign, morphology, sign of T2WI and axial location) were screened to facilitate the differential diagnosis. The capability of logistic equation analysis is 87.1%, indicating that these imaging findings may be useful for differential diagnosis of the two lesions.
Based on a certain finding only, such as sex, craniocaudal distribution, gave excellent results when evaluated with our series, but they were not included in the multivariate logistic equation. We harbor the idea that results are wonderful and
Fig. 5 54-year-old woman with intraspinal schwannoma at the C4–6 level. a, b Sagittal and axial T1WI without enhance-ment. c Sagittal T1WI with enhancement. d, e Coronal T1WI with fat-suppressed enhancement, and axial T1WI with enhancement. A miscel-laneous signal oval lesion with marked heterogeneity (rim with focal enhancement) was manifested in the left-postero-lateral area (white arrow), and it extended over several vertebra along the spinal canal (white arrow), there was a fluid–fluid level inside it (b and e, black arrowhead). The adjacent spinal cord was compressed to the right-anterolateral area (b and e, white arrowhead)
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it gets the most appropriate regression model; moreover, the multicollinearity does not exist anymore.
More than 95% of meningiomas were benign tumors and occurred most frequently in older women [4]. The female preponderance in the adult population was even stronger than that associated with intracranial meningiomas, and it was thought to be due to the effect of estrogen [11, 12].
Our results were partially conformed to the opinions: There were 43 (81.1%) meningioma patients with the age of 61–87 years, and there was a predominance in the female group (40, 75.5%).
Of meningiomas, 90% are intradural and only 10% are extradural or dumbbell tumors. Most spinal meningiomas (80%) arise in the thoracic region, with less common
Fig. 6 A 52-year-old man with intraspinal meningioma at the T2 level. a Sagittal T1WI without enhancement. b Coronal T1WI with fat-suppressed enhancement. An oval lesion manifested hypointense on T1WI (white arrow), marked rim enhancement in the right lateral area (white arrowhead), and the adjacent spinal cord was compressed to the dorsal area. A 70-year-old woman with intraspinal meningioma at the T11-12 level. c Sagittal T1WI without enhancement. d Coronal T1WI with fat-suppressed enhancement. An isointense round lesion (white arrow) with marked homogeneity enhancement was demon-strated in the right lateral area (white arrowhead), the adjacent spinal cord was compressed to the left. A 41-year-old man with two intraspi-
nal schwannomas in the lumbar. e Sagittal T2WI. f Coronal T1WI with fat-suppressed enhancement. The big lesion manifested fluid sig-nal intensity on T2WI (white arrow) with marked rim enhancement and septal enhancement (black arrowhead) and the round small lesion manifested isointense signal with marked homogenous enhancement (white arrowhead). A 55-year-old man with intraspinal schwannoma at the L1-2 level. g Sagittal T1WI without enhancement. h Coronal T1WI with fat-suppressed enhancement. An oval lesion manifested hypointense on T1WI (white arrow), marked rim enhancement with focal mural nodule enhancement in the right-anterolateral area (white arrowhead)
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involvement of the cervical (15%) or lumbar (5%) regions [10]. Meningiomas are often located posterolaterally in the thoracic region and anteriorly in the cervical region. 70% schwannomas are intradural, while 30% can be extradural. “Dumbbell” tumors are usually located both intradurally and extradurally. Intramedullary schwannomas are overwhelm-ingly rare [13].
The typical spinal meningioma is a small, single, dis-crete, round or oval intradural tumor, but occasionally it may present multiple lesion (2%). In general, schwannomas are solitary, well-circumscribed and encapsulated tumors, com-monly arising from the dorsal sensory roots of the cervical and lumbar spine with less frequent involvement of the tho-racic region and rarely occur in the lumbosacral region [12, 14]. Our work results do not fully correspond with previous reports. Schwannomas share quite a few imaging features of intraspinal meningiomas, such as solid, round or oval, well-circumscribed lesions (meningiomas vs. schwanno-mas, 50 vs. 63). Meningiomas were predominantly located thoracic regions, while schwannomas in the thoracic and the lumbar regions (P < 0.001). But there were 10 multiple lesions in the schwannoma group, none in the meningioma group. We hold the view that the reason may be the small number of samples for meningiomas. And there were 10 schwannomas in vertebral junction regions, not meningioma. Meningiomas often occurred in the ventral or anterolateral regions, while schwannomas in the posterolateral regions. We speculate that this may be associated with the origina-tion and the growth type of tumors. When the lesion is large, schwannoma may either extended with the long axis of the cord, forming a sausage-shaped mass which may extend over several levels (Fig. 5) or protrude out of the intervertebral foramen, forming a dumbbell-shaped mass (Fig. 3a) which often cause adjacent bones absorb and remodel.
Yamaguchi et al. concluded that the ginkgo leaf sign was highly specific to spinal meningiomas arising lateral or ventrolateral to the spinal cord [7]. An enlarged tumor will deform the spinal cord like a fan because the lateral side of the spinal cord is tethered to the dura by the stretched dentate ligament. Schwannomas did not demonstrate the ginkgo leaf sign, probably due to a difference in growth pattern [7]. In our examination, the ginkgo leaf sign was only found in two lateral or ventrolateral meningiomas (Fig. 3b).
A dumbbell shape with intervertebral foraminal widening was useful in differentiation, which occurred in 32 (30.8%) schwannomas in our work (P < 0.001). Meningiomas with foraminal widening were relatively rare, accounting for only 3–10% of all spinal meningiomas [15, 16]. Consistent with this finding, we observed only three meningiomas of the mild foraminal widening in this examine.
In our study, the size of schwannomas was more than that of meningiomas’, and there was significantly different between groups (P = 0.000). The cutoff value (> 1.88 cm)
was used to differentiate schwannoma from meningioma. The diagnostic PPV (90.6%) and SP (90.6%) were very high.
Wilms et al. first described the “dural tail sign” in 1989 only on enhanced MR images in association with cranial meningiomas [17]. Dural tail sign was initially thought to be highly specific for meningioma [9]. The sign is now con-sidered suggestive but not specific for meningioma [18–20]. Tien et al. held the view that a loculated leptomeningeal metastasis, sarcoidosis, lymphoma, or chloroma could mimic a meningioma with the dural tail sign. It was also possible that any type of lymphocytic or histiocytic infiltra-tion as well as granulomatosis could give a similar picture [21]. De Verdelhan et al. [22] argued that the dural tail sign was seen in 67% of the meningiomas and in the rare extra-dural meningiomas as well as in a recurrent meningioma. According to Alorainy et al., the “dural tail sign” was as common in spinal meningiomas as in cranial meningiomas [9]. In general, the “dural tail sign” was subtle and visible only on one or two slices. Detection of that sign requires acquisition cut planes demonstrating the dural contact of the tumor in its greatest length. Consequently, we suggest that coronal images (for lateral tumors) and sagittal images (for ventral or dorsal tumors) can be used to study the relation between the tumor and the dura, and to search for the “dural tail sign.” In our work, we found 32 (60.4%) meningiomas with the “dural tail sign,” only 6 (6.8%) schwannomas. Dural tail sign was beneficial for the diagnosis of spinal meningi-oma (P < 0.000).
Signal patterns on T1WI manifested iso- or hypointen-sity for schwannomas and iso- or hyperintensity for men-ingiomas with no statistical difference [23, 24]. But our results do not conform to these findings, 50 (94.3%) menin-giomas manifested isointensity, while 56 (53.8%) schwan-nomas cases did hypointensity, 6 cases hyperintense and 2 cases miscellaneous signal on T1WI. There is with statis-tical difference between meningiomas and schwannomas (P < 0.001). Indeed, most schwannomas were heterogeneous and exhibited relatively higher signal intensity than that of meningiomas’ on T2WIs [23]. However, Liu et al. reported that signal intensity of T2WI alone may be inadequate for differentiating between these lesion types [13].
Our results demonstrated that fluid signal intensity (cyst degeneration) and miscellaneous signal were frequently manifested in schwannomas (P < 0.001). Therefore, fluid signal intensity and signal heterogeneity of T2WI could be a useful predictor in diagnosing of schwannomas (Fig. 5). We speculate that focal areas of even greater hyperinten-sity on T2WI often corresponds to cystic portions, whereas hypointensity may represent hemorrhage, dense cellularity or collagen deposition [12, 25]. Schwannomas tendency to cyst formation and hemorrhage were greater in the spine than the intracranial examples and other extramedullary spi-nal tumors, such as meningiomas [26].
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In our series, all schwannomas and meningiomas were easily detected on contrast-enhanced MRI, and none of schwannomas or meningiomas were not enhanced. Schroth et al. [27]. reportedly observed no significant differences in contrast enhancement degree between spinal schwan-nomas and meningiomas. Our results are accord with this opinion: There is no significant statistical difference for the degree of enhancement (P = 0.336). Hence, we take the attitude that the degree of enhancement with Gd-DTPA is not considered a useful criterion for differentiation. But the contrast enhancement pattern demonstrated differences between meningiomas and schwannomas in our work, which may be considered an aid for differential diagnosis (P = 0.005).
Our examination was with several major limitations. The first and foremost, the study was retrospective, and the reviewers were all specialized in differentiating schwan-nomas from meningiomas, not include any cases of other intradural extramedullary tumors such as cysts, capillary hemangiomas, or ependymoma, which might possess the influenced sensitivity of MR imaging for differentiating the two lesion types. Therein one more point, the men-ingioma group involved in our study was the relatively small sample size. There was a significant difference in each MRI finding, it was possible that no type 2 error occurred (caused by small sample size). To eliminate these issues, we aimed to conduct a similar prospective study in a large cohort. Finally, because the cases were retrospec-tively collected over 8 years from two different types of MR machines, protocols were inevitably not standardized.
Conclusions
To sum up, simple clinical data associated with MRI findings can be used to an accurate diagnosis in the vast majority spinal meningiomas and schwannomas, if vari-ous imaging features are analyzed carefully and discreetly.
A thoracic vertebra canal tumor with diffuse homog-enous enhancement and the “dural tail sign” in females proved statistically significant as predictors of menin-gioma, while a tumor with widening of neural foramen, fluid signal intensity on T2WI, rim enhancement proved statistically significant as predictors of schwannoma, espe-cially occurred in vertebral junction regions or lumbar locations. When intraspinal tumors manifested multiple, this gave us confidence in diagnosis of schwannomas. In the future, diffusion-weighted imaging and susceptibility weighted imaging may increase the accuracy of imaging findings in the differentiation of spinal schwannomas and meningiomas.
Compliance with ethical standards
Conflict of interest No conflict of interest exists in the submission of this manuscript, and manuscript is approved by all authors for publica-tion. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part. All the authors listed have approved the manuscript that is en-closed.
Ethical approval All procedures performed in studies involving human participants were in accordance with the ethical standards of the insti-tutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent This retrospective study was approved by our insti-tutional review board, and the requirement for informed consent was waived.
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