Kumar et al. BMC Musculoskeletal Disorders (2017) 18:244 DOI 10.1186/s12891-017-1608-z REVIEW Open Access Magnetic resonance imaging of bacterial and tuberculous spondylodiscitis with associated complications and non- infectious spinal pathology mimicking infections: a pictorial review Yogesh Kumar1, Nishant Gupta2, Avneesh Chhabra3, Takeshi Fukuda4, Neetu Soni5 and Daichi Hayashi1,6* Abstract Magnetic resonance (MR) imaging plays an important role in the evaluation of bacterial and tuberculous spondylodiscitis and associated complications. Owing to its high sensitivity and specificity, it is a powerful diagnostic tool in the early diagnosis of ongoing infections, and thus provides help in prompt initiation of appropriate, therapy which may be medical or surgical, by defining the extent of involvement and detection of complications such as epidural and paraspinal abscesses. More specifically, MR imaging helps in differentiating bacterial from tuberculous infections and enables follow up of progression or resolution after appropriate treatment. However, other non-infectious pathology can demonstrate similar MR imaging appearances and one should be aware of these potential mimickers when interpreting MR images. Radiologists and other clinicians need to be aware of these potential mimics, which include such pathologies as Modic type I degenerative changes, trauma, metastatic disease and amyloidosis. In this pictorial review, we will describe and illustrate imaging findings of bacterial and tuberculous spondylodiscitis, their complications and non-infectious pathologies that mimic these spinal infections. Keywords: Spine, Infection, Abscess, MRI, Spondylitis, Discitis Background be aware of these potential mimickers when interpreting Magnetic resonance (MR) imaging plays an important MR images [6–10]. Radiologists and referring clinicians role in the evaluation of bacterial and tuberculous spon- need to be aware of these potential mimics, which in- dylodiscitis. Owing to its high sensitivity and specificity clude such pathologies as Modic type I degenerative of up to 90% or greater [1–5], it is a powerful diagnostic changes, trauma, metastatic disease and amyloidosis. In tool in the early diagnosis of spondylodiscitis. MR im- this pictorial review, we describe and illustrate imaging aging thus provides help in prompt initiation of appro- findings of bacterial and tuberculous spondylodiscitis, priate therapy which may be medical or surgical, by their complications and non-infectious pathologies that defining the extent of involvement and detection of mimic these infections. complications such as epidural and paraspinal abscesses. However, other non-infectious pathology can demon- Epidemiology of bacterial and tuberculous strate similar MR imaging appearances and one should spondylodiscitis In bacterial spondylodiscitis, Staphylococcus aureus is * Correspondence: [email protected] the most commonly responsible organism, accounting 1Department of Radiology, Yale New Haven Health System at Bridgeport for up to >75% of cases [11–13]. Other organisms that Hospital, 267 Grant Street, Bridgeport 06610, CT, USA may cause bacterial spondylodiscitis include Escherichia 6Department of Radiology, Boston University School of Medicine, 820 Harrison Avenue, FGH Building 3rd Floor, Boston 02118, MA, USA coli in patients with concurrent urinary tract infections, Full list of author information is available at the end of the article Pseudomonas aeruginosa in patients with a history of © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Kumar et al. BMC Musculoskeletal Disorders (2017) 18:244 Page 2 of 10 intravenous drug abuse, Streptococcus pneumoniae in Clinical presentation and diagnostic work-up patients with diabetes, and Salmonella species in pa- Bacterial spondylodiscitis most commonly presents with tients with sickle cell disease or asplenia [14, 15]. acute to subacute onset of back pain and fever. In many Tuberculosis (TB) is one of the major causes of morbid- cases, fever of unknown origin is the main presenting ity and mortality in developing countries with a rising complaint. Progressively increasing pain at the surgical trend in the United States and other developed countries site is usually the first symptom of postsurgical infection. with a reported worldwide incidence of 10.4 million cases For tuberculous spondylitis, patients present with consti- in 2015 according to the World Health Organization glo- tutional symptoms such as malaise, loss of weight and bal report [16]. Spinal TB is a destructive form of TB night sweats while in chronic healed stage patients present affecting the spinal column in less than 1% of all TB cases, with back stiffness, deformity and neural deficits. causing neurological deficits, spinal deformities and para- Laboratory evaluation includes elevated inflammatory plegia which mandates early diagnosis and treatment to markers such as erythrocyte sedimentation rate (ESR) and avoid permanent damages [17]. According to an epi- C-reactive protein (CRP). These are very sensitive but demiological study in the United States with a 10-year ob- non-specific markers of active bacterial spondylodiscitis, servation period (2002–2011), the incidence of spinal TB and thus can only be used to exclude active infection. is actually decreasing from 0.07 cases per 100,000 persons Moreover, normal levels can also be seen in chronic infec- in 2002 to 0.05 cases per 100,000 in 2011 (p <0.001),cor- tions. Leukocytosis and positive blood cultures are seen in responding to 1 case per 2 million persons in the latter most cases, especially before the initiation of medical year [18]. The same study identified men aged approxi- treatment. Diagnosis of TB infection is usually based on mately 50 years were most commonly affected [18]. clinical features, cerebrospinal fluid (CSF) analysis, hist- ology and culture. However, combined use of MR imaging Pathogenesis of bacterial and tuberculous and GeneXpert, a test which detects DNA sequences spe- spondylodiscitis cific for Mycobacterium tuberculosis increases the sensitiv- Bacterial spondylodiscitis usually occurs due to ity to 97.9% for detection [17]. In doubtful cases, tissue hematogenous spread from a distant site, particularly biopsy is required to reach the diagnosis. from the lung or urinary tract. Bacterial spondylodiscitis The diagnosis is often made by a combination of clinical can also occur via direct extension, for instance from features and imaging findings in some cases of spinal in- spinal surgery, myelography, penetrating trauma, and fection to initiate early empirical treatment in order to re- from adjacent infections in the thorax or abdomen. Due duce the risk of complications, such as vertebral collapse to differences in vascular anatomy at different stages of and cord compression. However, a definitive diagnosis of life, discs are usually the first site of infection in the causative micro-organism is very difficult to establish pediatric patients followed by metaphyseal involvement, based on clinical features and imaging alone. Therefore, while in adult patients endplates are usually the first site image-guided percutaneous spinal biopsies are being in- of infection followed by disc involvement [19, 20]. creasingly performed to get sufficient tissue for culture Tuberculous spondylodiscitis, also known as Pott dis- and sensitivity of the causative organism [24]. However, ease, is caused by Mycobacterium tuberculosis, a slow- the biopsy diagnostic yield of percutaneous spinal biopsy growing gram positive acid fast bacillus which becomes for detecting infection ranges from 30 to 40% and aspir- lodged in the bone via Batson’s venous plexus and ation of > or = 2 mL of purulent fluid reported increases lymphatic from primarily infected lung, lymph nodes, the rate of positive cultures [24]. mediastinum and viscera, forming granulomatous in- flammation and caseation necrosis [17]. Primary or sec- Technical considerations for MR imaging ondary involvement of the posterior appendicular and Usually, MR imaging of the spine is performed with articular element along with paraspinal soft tissue can basic sequences including T1 and T2 weighted sagittal also be seen [17, 21]. Thoracolumbar region is the most and axial images. Additionally, fat-suppressed T2- commonly affected site while the cervical and sacrum weighted sequence or Short tau Inversion Recovery regions are less commonly involved. Usually more than (STIR) sequence is used to increase the conspicuity of one vertebra is affected because of its segmental arterial bone marrow edema and thus increasing the sensitivity distribution and subligamentous spread of the disease. [6]. If there is no bone marrow edema on fat suppressed The bacilli reach the disc space causing disc destruction, T2-weighted or STIR images, gadolinium contrast ad- spreads to adjacent vertebral bodies leading to vertebral ministration does not add any value and is not required collapse, anterior wedging,