Management of spinal infection: a review of the literature

Intramedullary spinal cord abscesses (ISCA) are very rare with about 120 reported cases since the first description in 1830 [49]. Congenital dermal sinus is implicated as the leading cause of ISCA in children, whereas hematogenous spread of urogenital and lung infections or infective endocarditis is the most common cause in adults. Usually some underlying spinal (cord) pathology provides the basis for ISCA [80]. The overall mortality of ISCA has improved significantly from 90% in 1944 [8] to 4% in 2009 [49], mostly caused by the availability of sufficient diagnostic facilities, the use of antibiotic agents, and improved surgical techniques. Due to the small number of cases, there is no general algorithm for ISCA and treatment has to be chosen diligently according to the patient’s clinical status. Generally, early drainage and the rapid administration of intravenous antibiotics result in a good prognosis [40]. Surgical drainage within 5 days after onset of symptoms may lead to a significantly better neurological outcome than conservative treatment or delayed drainage [40, 75].

Subdural empyema (SDE), known as an infection located between the dura and the arachnoid, is a very rare condition and mostly results from hematogenous infection or spread of infection from osteomyelitis [36]. SDE may develop in the spinal canal where it is possible to cause rapid compression of the spinal cord. The diagnostic procedure of choice is MRI with gadolinium, followed by CT with myelography [50, 63]. Early surgical drainage followed by appropriate antibiotic therapy is the most promising treatment [10]. Depending on the extension of the lesion, (hemi-)laminectomy over one or more levels may be necessary. In cases of wider spread, flavectomy or laminotomy at several different levels may be required in order to evacuate the infectious material [2, 50]. Generally, SDE represents an extreme medical and neurosurgical emergency and treatment requires prompt surgical drainage and antibiotic therapy, as morbidity and mortality in SDE relate directly to treatment delay. As soon as the central nervous system is directly involved, outcome is poor [69]. Thus, the condition should be treated with great urgency [36].

Spinal epidural abscess (SEA) also is a life-threatening infection. Mortality rates are estimated at 5–16% worldwide, and less than 50% of surviving patients show full recovery. Although SEA is a relatively rare diagnosis (2.5–3.0/100,000), the incidence has nearly doubled in the last 50 years according to circumstances already mentioned above and an increasing incidence of SI in general [6, 71]. Demographically, male patients are affected more frequently than female patients (ratio 2:1) for unknown reasons. Furthermore, a peak is reported in the sixth decade of life [66]. Spontaneous SEA is mostly a secondary complication of a primary SI like spondylodiscitis, spreading hematogenously via septic thrombosis of epidural veins [37]. Alternatively, iatrogenic SEA is mainly associated with surgical spinal procedures and in particular with epidural anesthesia or spinal injections [56]. Abscesses are most commonly located in the lumbar spine (48%), followed by the thoracic (31%) and the cervical spine (24%) [6]. Mostly, SEAs present as a multisegmental (three to four segments) disease as germs are capable of spreading via the epidural space without anatomical resistance. SEA is found in multiple locations in 20% of cases; therefore, imaging of the whole spine is recommended [19]. As soon as an active infection is suspected, treatment should be started immediately. Decompression combined with systemic antibiotics has been established as gold standard in the last decades, especially in patients with progressive infection and late diagnosis [6]. Nevertheless, management should be guided by individual parameters, as recently good outcomes were also demonstrated for conservative treatment. Conservative management can be considered (1) in patients with severe comorbidities which limit surgical options, (2) in extremely lengthy SEA (holospinal), in which surgery may not make sense or may be unachievable, (3) when SEA is detected early and patients suffer from no or only minor neurologic deficits, or (4) when the patient presents with complete paralysis for more than 72 h [66]. However, 6–49% of initially conservatively treated patients still show progression of neurologic deficits, so that treatment has to be reconsidered carefully after meticulous re-evaluation [6, 19]. Special attention should be paid to patients suffering from high-risk factors for failure of medical treatment. Those include diabetes mellitus, MRSA infection, neurological impairment involving the spinal cord, acute or progressive deficit, CRP > 115 mg/L, WBC count > 12.5 × 10⁹ cells/L, ring-like enhancement on MRI, and bacteraemia. Non-operative treatment should only be offered with close monitoring as the initial line of treatment and does not guarantee the prevention of operative therapy [83]. Surgical options for the treatment of SEA include minimally invasive or endoscopic procedures, multisegmental decompression, instrumentation, and ventral debridement of the disc. The choice of the surgical approach depends on the consistency of the space-occupying lesion: solid (granulation tissue) or liquid (abscess). Dorsally accessible abscesses call for a minimally invasive drainage via laminotomy and irrigation, whereas dorsally located granulation tissue should be treated with multisegmental decompression and/or resection. Apart from that, ventrally located granulation tissue, which is usually associated with spondylodiscitis, is most effectively treated by corpectomy, reconstruction, and instrumentation [15]. Overall, patients being surgically treated show a good outcome in more than 60%. Those convincing results cause some authors to recommend surgical therapy of SEA even without associated neurological deficits and especially when lesions are located in the cervical or thoracic spine. As mortality of SEA is still reported to be 5–20%, therapeutic decisions have to be made promptly and thoughtfully and influencing outcome predictors have to be considered. It has to be realized that SEA treated with medical management alone has a high risk for failure, if the patient is older than 50 years and suffers from severe comorbidities like diabetes or MRSA infection and neurologic compromise. In the absence of these risk factors, non-operative management may be considered as the initial line of treatment, but only with very close monitoring [45, 64]. Nevertheless, surgery should stay the treatment of choice in any case of doubt.

Spondylodiscitis is defined as an infection of the disc and the adjacent vertebrae, mostly (55–80%) caused by Staphylococcus aureus and spread hematogeneously [20]. The infection can emerge primarily or secondarily, due to spinal interventions, whereas primary acquired spondylodiscitis shows a more severe course and significantly higher mortality rate (12.5 vs. 1.8%) than postoperative infections [81]. Incidence ranges from 0.2 to 2.4/100,000 in western countries [15, 32], and male patients are affected twice as often as females [87]. At clinical presentation, the average age is the fifth to sixth decade, and symptoms are frequently unspecific. Unfortunately, this often leads to a delay in diagnosis and may explain why mortality still ranges between 2 and 20% [76, 87]. Hence, spondylodiscitis has to be seen as a life-threatening condition and treated as an emergency. Although some guidelines for treatment are available, therapy for spondylodiscitis is not standardized and based on individual preferences. In general, treatment goals have to predominantly include the control of the infection by treatment of the causative systemic disease and removal of the septic focus. The first-line treatment of choice is a conservative attempt, which is absolutely reasonable in early stage with no, or minor, neurologic deficits and in case of severe comorbidities, which limit surgical options. Initially, Clindamycin + Ciprofloxacin or Cefotaxim + Flucloxacillin are highly recommended to cover a preferably wide spectrum of potential pathogens [27]. Subsequently, therapy has to, of course, be adjusted to results of bacteriologic test results. Appropriate antibiotics should be applied intravenously for 2–4 weeks or until CRP has largely dropped. Thereafter, oral antibiotic treatment is continued for a total of 6 to 12 weeks [27, 76]. Duration and route of administration of antibiotic treatment are still matter of debate, since a relationship between treatment duration and relapse/failure is assumed. Additionally, conservative treatment should include bed rest and/or orthosis for at least 6 weeks, depending on pain upon mobilization [15]. Conservative therapeutic options are successful in many cases, but are not always sufficient. Surgery has to be considered when medical options have failed and symptoms or imaging findings show progress. Some cases may initially require surgical debridement and stabilization. Rapid surgical treatment is mandatory if patients present with advanced stage spondylodiscitis, neurologic deficits, progressive septicaemia, and/or progressive instability or deformity (Table 1). If mobilization fails due to pain in conservatively treated patients, many surgeons nowadays proceed with surgery, as complications of immobilization can be critical in this comorbid population. Classically, an anterior open debridement and, mostly, instrumentation have been the preferred treatment, associated with good outcome and low intraoperative complication rates [32]. Recently, promising techniques improving outcome and lowering complications have been described. Particularly in cervical spondylodiscitis, a single anterior approach has become more and more applicable [67, 73]. However, in cases of extensive involvement requiring multiple corpectomies, a combined anterior and posterior approach is appropriate (Fig. 3). In clinical situations, in which an anterior approach is contraindicated, posterior transforaminal or posterior interbody debridement and fusion can be considered, mostly in cases of lumbar discitis and/or minimal vertebral involvement [26]. Moreover, posterior stabilization and interbody fusion are feasible in elderly high-risk patients with spondylodiscitis and septic complications. Even though it may not be the therapy of first choice in high-risk septic patients, it may be considered in patients when conservative management has failed [38]. Attention should be paid to the method of interbody fusion, as a direct correlation of autologous graft infection to comorbidities and patient’s age has been shown [62]. Minimally invasive disc debridement may lead to immediate pain reduction and good clinical results in patients who suffer from comorbid medical problems and pyogenic spondylodiscitis [39]. Even minimally invasive combined approaches for instrumentation lead to good outcomes in suitable patients, as the technique results in little surgical trauma, intraoperative blood loss, and few postoperative complications. Therefore, the approach is effective and safe for the treatment of single-level lumbar pyogenic spondylodiscitis and could be an alternative to conventional open surgery [55]. Overall benefits of minimally invasive debridement and instrumentation include less blood loss, less spread of infection, less wound infection, and may ultimately lead to more rapid fusion and therefore to faster recovery. Percutaneous instrumentation may only be a valuable option in patients showing no space-occupying abscess and lacking deformity and/or pathologic fracture (Fig. 4) [21]. Percutaneous pedicle screw instrumentation (1) without any debridement [21], (2) with minimally invasive decompression and debridement, or (3) with a second anterolateral debridement/corpectomy is increasingly used [78].

Additional antibiotic treatment (modified to intraoperative culture results) has to be administered for at least 6 to 12 weeks in all cases [27]. The final result in conservative as well as in surgical treatment always is bony fusion, so that conservative management does not preserve segmental motion.

The most common paraspinal site of infection, the iliopsoas abscess (IPA) can be subdivided in primary and secondary acquired disease. Primarily arisen IPA is a rare condition and mostly occurs due to hematogenous or lymphatic spread of a pathogen from a distant infectious site. On the contrast, the majority of cases seen represent secondary IPA, most commonly caused by inflammatory spinal or skeletal pathology [72]. The recommended first-line therapy is broad spectrum antibiotic therapy, covering Staph. aureus as the most frequent pathogen accountable for IPA [60]. Especially small abscesses (< 3 cm) may be treated efficiently with antibiotic therapy alone [86]. In the case of progress or insufficient medical therapy, image-guided percutaneous drainage is a very effective and safe alternative to the open surgical drainage [22]. Nevertheless, in secondarily acquired, multiloculated IPA accompanied by florid spinal infection, open surgical drainage plus treatment of the underlying cause is the treatment of choice [58].