Department of Diagnostic Radiology, Sohag Faculty of Medicine, Sohag University, Sohag, Egypt

Transcription

1 Journal of Orthopaedic Surgery 2011;19(2): Sensitivity, specificity and accuracy of magnetic resonance imaging for differentiating vertebral compression caused by malignancy, osteoporosis, and infections ME Abdel-Wanis, 1 Mohamed Tharwat Mahmoud Solyman, 2 Nahla Mohamed Ali Hasan 2 1 Department of Orthopaedic Surgery, Sohag Faculty of Medicine, Sohag University, Sohag, Egypt 2 Department of Diagnostic Radiology, Sohag Faculty of Medicine, Sohag University, Sohag, Egypt ABSTRACT Purpose. To evaluate the sensitivity, specificity and accuracy of various magnetic resonance imaging (MRI) features in differentiating vertebral compression caused by malignancy, osteoporosis, and infections. Methods. 35 men and 45 women aged 40 to 78 (mean, 59) years underwent MRI to assess the underlying pathology of already diagnosed vertebral compression (n=152). The interval from presentation to imaging ranged from 7 to 95 (mean, 62) days. MRI features of each vertebral compression fracture were assessed. The sensitivity, specificity, and accuracy for each of the MRI features were calculated. Association between each MRI feature and various underlying pathologies (malignancy, osteoporosis, and infections) of vertebral compression was evaluated. Results. Regarding these 80 patients, the MRI diagnosis was correct in 78 and inconclusive in 2 with malignancy. MRI features suggestive of malignant were a convex posterior border of the vertebral body, pedicle involvement, posterior neural element involvement, an epidural mass, a paraspinal mass, and other spinal metastases. MRI features suggestive of osteoporotic were retropulsion, low signal intensity band, spared normal marrow signal intensity, and the fluid sign. MRI features suggestive of infective were contiguous vertebral involvement, end plate disruption, disc involvement, and paraspinal and epidural abscesses. Conclusion. Combination of several MRI features can provide clues to differentiate between malignant, osteoporotic, and infective vertebral compression. Key words:, compression; infection; magnetic resonance imaging; neoplasm metastasis; osteoporosis; osteoporotic ; spinal INTRODUCTION Vertebral compression are common, Address correspondence and reprint requests to: Dr ME Abdel-Wanis, Department of Orthopaedic Surgery, Sohag Faculty of Medicine, Sohag, PO 82524, Egypt. wanis307@yahoo.com

2 146 ME Abdel-Wanis Journal of Orthopaedic Surgery especially in the elderly. Differentiating malignant from benign compression based on clinical findings, radiography, bone scans, and computed tomography may not be sufficient, particularly for patients without a history of trauma or malignancy. Magnetic resonance imaging (MRI) features for differentiating benign and malignant spinal compression have been reported. 1 5 Most such studies only included osteoporotic as the benign entity 2 4 ; few included infective vertebral. 5 Also, the relative importance, sensitivity, specificity, and accuracy of several MRI criteria are not fully established. We evaluated the sensitivity, specificity and accuracy of various MRI features in differentiating vertebral compression caused by malignancy, osteoporosis, or infections. MATERIALS AND METHODS From May 2003 to May 2007, 35 men and 45 women aged 40 to 78 (mean, 59) years presented with back or neck pain and/or a neurological deficit after no or minor trauma (e.g. fall from standing height). They underwent MRI to assess the underlying pathology of the already diagnosed vertebral compression (n=152). The interval from presentation to imaging ranged from 7 to 95 (mean, 62) days. MRI was performed using a 1.5-tesla imager (Gyro ACS.NT synergy coil MR device-philips) or a 0.2-tesla imager (Concerto Version syngo MR 2004A-Siemens). Gadolinium-diethylenetriamine pentacetic acid (Gd-DTPA) of 0.2 ml/kg body weight 6 was administered intravenously after conventional T1- and T2-weighted sequences are completed. Various MRI features of each vertebral compression fracture were assessed. They included (1) bone marrow replacement 4,7 : (i) complete replacement (no normal bone marrow signal in the compressed vertebra), (ii) incomplete replacement (some residual normal bone marrow signal), and (iii) complete preservation (only normal bone marrow signal); (2) convex posterior vertebral border; (3) pedicle involvement; (4) posterior element involvement; (5) other metastatic lesions (denoted by abnormal signal intensity in the bone marrow of other vertebrae) 3 ; (6) retropulsion of a posterior bone fragment (often posterosuperior angle of the vertebral body into the spinal canal) 8 ; (7) a low signal intensity band like area on T1- and T2-weighted images corresponding to a fracture line or trabecular impaction; (8) a fluid sign: focal, linear or triangular areas of high signal intensity adjacent to the vertebral end plates on T2-weighted and short T1 inversion recovery images 1,8,9 ; (9) contiguous vertebral involvement; (10) vertebral end plate integrity; (11) vertebral disc involvement (manifest as an abnormal signal intensity pattern: hypointense on T1-weighted images and hyperintense on T2- weighted and post-contrast enhancement images) and reduced disc height; (12) epidural mass (anterior, posterior or encasing); (13) a paraspinal soft-tissue mass (anterior, posterior or both); (14) a paraspinal abscess; and (15) an epidural abscess. Both abscesses and soft-tissue masses exhibit low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, but soft-tissue masses are enhanced by Gd-DTPA whereas abscesses show ring enhancement. 2,10 The sensitivity (true positive / [true positive + false negative] x100), specificity (true negative / [true negative + false positive] x100), and accuracy (number of correct MRI diagnosis / number of confirmed final diagnosis x100) for each MRI feature were calculated. Associations between each MRI feature and various underlying vertebral compression fracture pathologies were evaluated using the Chi squared test. A p value of <0.05 was considered statistically significant. Table 1 Diagnoses of vertebral compression based on magnetic resonance imaging (MRI) Diagnostic result Malignant No. (%) of patients Osteoporotic Infective Correct 48 (96) 16 (100) 14 (100) Inconclusive 2 (4) 0 0 Incorrect Table 2 Primary tumour diagnoses of 50 patients presented with 85 malignant vertebral compression Tumour origin No. (%) of patients No. (%) of Breast 13 (26) 29 (34) Myeloma 7 (14) 12 (14) Liver 4 (8) 4 (5) Lung 4 (8) 8 (9) Lymphoma 4 (8) 8 (9) Prostate 4 (8) 4 (5) Thyroid 3 (6) 5 (6) Kidney 2 (4) 2 (2) Colon 1(2) 1 (1) Uterus 1(2) 3 (4) Unknown 7 (14) 9 (11) Total 50 (100) 85 (100)

3 Vol. 19 No. 2, August 2011 MRI for differentiating malignant, osteoporotic, and infective vertebral compression 147 Table 3 Magnetic resonance imaging (MRI) features suggestive of malignant, osteoporotic, and infective vertebral compression MRI feature No. (%) of (n=152) p Value Sensitivity Malignant Osteoporotic Infective (%) (n=85) (n=34) (n=33) Specificity (%) Accuracy (%) Malignant Convex posterior border 60 (71) 1 (3) 0 < Pedicle involvement 81 (95) 5 (15) 15 (46) < Posterior elements involvement 61 (72) 0 9 (27) < Epidural mass 51 (60) Paraspinal mass 68 (80) 4 (12) 5 (15) < Other spinal metastases 65 (77) Osteoporotic Retropulsion 0 18 (53) 2 (6) < Low signal intensity band 8 (9) 28 (82) 2 (6) < Spared normal marrow signal 6 (7) 27 (79) 6 (18) < intensity Fluid sign 2 (2) 12 (35) 0 < Infective Contiguous vertebral involvement 20 (24) 12 (35) 29 (88) < End plate disruption 4 (5) 0 27 (82) < Disc involvement 2 (2) 0 32 (97) < Paraspinal abscess (85) Epidural abscess (73) RESULTS Regarding these 80 patients, the MRI diagnosis was correct in 78 and inconclusive in 2 with malignancy (Table 1). In 50 patients, the underlying pathology of 85 vertebral compression was malignancy (Table 2). In 45 of them, the final diagnosis was confirmed histopathologically through open biopsy. In the remaining 5, it was based on progressive deterioration of the fractured vertebra and/or new development of spinal metastases evident with followup MRI. Indications for surgery were interactable pain, neurological deficits, and a confirmed tissue diagnosis. In 16 patients, the underlying pathology of 34 vertebral compression was osteoporosis. In 14 of them, the final diagnosis was based on clinical and radiological follow-up over 6 to 12 months. In the remaining 2, it was confirmed histopathologically. Indication for surgery was neurological deficits. In 14 patients, the underlying pathology of 33 vertebral compression was infection. Their final diagnoses were confirmed histopathologically. The indications for surgery were interactable pain, severe or progressive kyphosis, a large abscess, and spinal instability. MRI features suggestive of malignant were a convex posterior border of the vertebral body, pedicle involvement, posterior neural element involvement, an epidural mass, a paraspinal mass, and other spinal metastases (Table 3 and Fig. 1). MRI features suggestive of osteoporotic were retropulsion, a low signal intensity band, spared normal marrow signal intensity, and the fluid sign (Table 3 and Fig. 2). MRI features suggestive of infective were contiguous vertebral involvement, end plate disruption, disc involvement, paraspinal abscesses, and epidural abscesses (Table 3 and Fig. 3). DISCUSSION MRI is superior to other diagnostic tools in differentiating benign from malignant compression spinal, 1 based on several MRI features. 2 9 However, only a few studies reported the sensitivity, specificity, and accuracy of each feature, 1,3 which enable the surgeon to prioritise the MRI features in case of contradiction. For example in our study, the most accurate MRI feature for diagnosis of infective was disc involvement. Its sensitivity, specificity and accuracy were 97%, 98% and 98%, respectively. If this feature is present, the addition of one or 2 other features suggestive of infection will be sufficient for diagnosis. Combination of several MRI features strongly affirms the diagnosis of spinal compression. 1 Compared to a study in 2009, 1 our study comprised a higher number of compression (152 vs. 58), and the were classified into 3 categories (malignancy, osteoporosis, and infection), rather than 2 (malignant vs. benign) categories, in

4 148 ME Abdel-Wanis Journal of Orthopaedic Surgery which the benign category (23 patients) included trauma and infection. In our study, the final diagnosis in 75% of patients was based on biopsy, compared to 22%. Biopsy is the gold standard for final diagnosis of vertebral compression. A study reported 3 patients who were provisionally diagnosed as having osteoporotic fracture, which was discovered by biopsy during vertebroplasty and kyphoplasty to be malignant caused by lymphoma. 11 In another study, the presumed aetiology in 18% of cases was not confirmed on pathological examination. 12 In fact, a biopsy picture suggestive of chronic osteomyelitis was reported in 6 (11%) out of 66 patients diagnosed as having osteoporotic spinal. 13 Because the accuracy of percutaneous vertebral biopsy was reported to be 80 to 90%, 14 our study should be considered accurate, as diagnoses of 75% of patients were made by open biopsy. Our study may help develop an MRI score to differentiate compression caused by (a) (b) (c) (d) Figure 1 (a) Sagittal T1-weighted, (b) T2-weighted (c) short T1 inversion recovery, and (d) axial (L5) T2-weighted magnetic resonance images (MRI) of the lumbosacral spine in a 46-year-old woman: the compression fracture of the L5 vertebral body shows complete replacement of normal marrow signal intensity, convex posterior border (arrows), involvement of the pedicles and transverse processes (asterisk), and metastases affecting L3 and L4 vertebrae (arrowheads). The MRI diagnosis is metastases affecting L3, L4, and L5 vertebrae complicated with compression fracture of L5. The final diagnosis is metastatic compression fracture of L5 originating from breast cancer. (a) (b) (c) (d) Figure 2 Sagittal (a) T1-weighted, (b) T2-weighted, (c) short T1 inversion recovery, and (d) axial (L2 and L3) T2-weighted magnetic resonance images (MRI) of the lumbosacral spine in a 60-year-old woman: compression of L2 and L3 show anterior wedging of the L2 vertebral body, low signal fracture line at L2 and L3, fluid sign at L3, and incomplete replacement of normal marrow signal intensity. The MRI diagnosis is L2 and L3 acute osteoporotic compression, which is also the final diagnosis.

5 Vol. 19 No. 2, August 2011 MRI for differentiating malignant, osteoporotic, and infective vertebral compression 149 (a) (b) (c) (d) (e) (f) (g) Figure 3 Sagittal (a) T1-weighted, (b) T1-weighted after gadolinium-diethylenetriamine pentacetic acid (Gd-DTPA) injection, (c) T2-weighted, (d) short T1 inversion recovery, and axial (e) T1-weighted, (f) T1-weighted after Gd-DTPA injection, (g) T2- weighted magnetic resonance images (MRI) of the thoracic spine in a 54-year-old woman: compression of T5 and T6 show contiguous vertebral involvement, complete replacement of normal bone marrow signal intensity, involvement of both pedicles (arrows), intervening disc involvement, and an encasing epidural mass and multiple paraspinal masses (arrowhead). The MRI diagnosis is spondylodiscitis affecting T5 and T6 and intervening disc complicated with vertebral compression. The final diagnosis is compression of T5 and T6 caused by tuberculosis infection (Pott s disease). malignancy, osteoporosis, and infection. Another study also tried to develop a scoring system based on MRI and computed tomography to facilitate differentiation between malignant and benign. 15 The most important MRI features for differentiation were pedicle or other posterior element involvement, expansion to the paravertebral region, preservation of normal bone marrow, and continuous black line of the posterior vertebral body margin on T2-weighted image. 15 The first 2 features suggestive of malignant were given the score of -3, whereas latter 2 features suggestive of benign were given the score In our study, all such features except the last had high sensitivity and specificity. In conclusion, combination of several MRI features can give the clue to differentiate between malignant, osteoporotic, and infective vertebral compression. REFERENCES 1. Pongpornsup S, Wajanawichakorn P, Danchaivijitr N. Benign versus malignant compression fracture: a diagnostic accuracy of magnetic resonance imaging. J Med Assoc Thai 2009;92: Fu TS, Chen LH, Liao JC, Lai PL, Niu CC, Chen WJ. Magnetic resonance imaging characteristics of benign and malignant vertebral. Chang Gung Med J 2004;27: Jung HS, Jee WH, McCauley TR, Ha KY, Choi KH. Discrimination of metastatic from acute osteoporotic compression spinal with MR imaging. Radiographics 2003;23: Rupp RE, Ebraheim NA, Coombs RJ. Magnetic resonance imaging differentiation of compression spine or vertebral lesions caused by osteoporosis or tumor. Spine (Phila Pa 1976) 1995;20:

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