Intervertebral instability of the lumbar spine is thought to be a possible pathomechanical mechanism underlying low back pain and sciatica and is often an important factor in determining surgical indication for spinal fusion and decompression. Instability of the lumbar spine, however, remains a controversial and poorly understood topic. At present, much controversy exists regarding the proper definition of the condition, the best diagnostic methods, and the most efficacious treatment approaches. Clinical presentation is not specific, and the relationship between radiologic evidence of instability and its symptoms is controversial. Because of its simplicity, low expense, and pervasive availability, functional flexion-extension radiography is the most thoroughly studied and the most widely used method in the imaging diagnosis of lumbar intervertebral instability. In this article, we provide an overview of the current concepts of vertebral instability, focusing on degenerative lumbar intervertebral instability, and review the different imaging modalities most indicated in diagnosing vertebral instability.

Spondylolysis is an osseous defect of the pars interarticularis, thought to be a developmental or acquired stress fracture secondary to chronic low-grade trauma. It is encountered most frequently in adolescents, most commonly involving the lower lumbar spine, with particularly high prevalence among athletes involved in certain sports or activities. Spondylolysis can be asymptomatic or can be a cause of spine instability, back pain, and radiculopathy. The biomechanics and pathophysiology of spondylolysis are complex and debated. Imaging is utilized to detect spondylolysis, distinguish acute and active lesions from chronic inactive non-union, help establish prognosis, guide treatment, and to assess bony healing. Radiography with satisfactory technical quality can often demonstrate a pars defect. Multislice CT with multiplanar reformats is the most accurate modality for detecting the bony defect and may also be used for assessment of osseous healing; however, as with radiographs, it is not sensitive for detection of the early edematous stress response without a fracture line and exposes the patient to ionizing radiation. Magnetic resonance (MR) imaging should be used as the primary investigation for adolescents with back pain and suspected stress reactions of the lumbar pars interarticularis. Several imaging pitfalls render MR imaging less sensitive than CT for directly visualizing the pars defects (regional degenerative changes and sclerosis). Nevertheless, the presence of bone marrow edema on fluid-sensitive images is an important early finding that may suggest stress response without a visible fracture line. Moreover, MR is the imaging modality of choice for identifying associated nerve root compression. Single-photon emission computed tomography (SPECT) use is limited by a high rate of false-positive and false-negative results and by considerable ionizing radiation exposure. In this article, we provide a review of the current concepts regarding spondylolysis, its epidemiology, pathogenesis, and general treatment guidelines, as well as a detailed review and discussion of the imaging principles for the diagnosis and follow-up of this condition.

Vertebral hemangiomas (VHs) are a frequent and often incidental finding on computed tomography (CT) and magnetic resonance (MR) imaging of the spine. When their imaging appearance is "typical" (coarsened vertical trabeculae on radiographic and CT images, hyperintensity on T1- and T2-weighted MR images), the radiological diagnosis is straightforward. Nonetheless, VHs might also display an "atypical" appearance on MR imaging because of their histological features (amount of fat, vessels, and interstitial edema). Although the majority of VHs are asymptomatic and quiescent lesions, they can exhibit active behaviors, including growing quickly, extending beyond the vertebral body, and invading the paravertebral and/or epidural space with possible compression of the spinal cord and/or nerve roots ("aggressive" VHs). These "atypical" and "aggressive" VHs are a radiological challenge since they can mimic primary bony malignancies or metastases. CT plays a central role in the workup of atypical VHs, being the most appropriate imaging modality to highlight the polka-dot appearance that is representative of them. When aggressive VHs are suspected, both CT and MR are needed. MR is the best imaging modality to characterize the epidural and/or soft-tissue component, helping in the differential diagnosis. Angiography is a useful imaging adjunct for evaluating and even treating aggressive VHs. The primary objectives of this review article are to summarize the clinical, pathological, and imaging features of VHs, as well as the treatment options, and to provide a practical guide for the differential diagnosis, focusing on the rationale assessment of the findings from radiography, CT, and MR imaging.

SummaryTreating complex aortic arch disease with proximal and distal aortic segment involvement is challenging. In recent years, different surgical and endovascular techniques have been applied in a single or multiple-stage approach with the aim to cure and simplify these conditions. The first procedure available for this purpose was the conventional elephant trunk technique. Its recent evolution is the frozen elephant trunk, which treats the descending thoracic aorta using the antegrade release of a self-expandable stent graft. In the following review article, we analyse the advantages and drawbacks of both techniques from clinical and practical perspectives.

OBJECTIVES We compared the results of 2 groups of patients who underwent aortic arch replacement with the frozen elephant trunk technique. In the first group, the distal anastomosis was performed in arch zone 2; in the second control group, the distal anastomosis was performed in arch zone 3. METHODS Between January 2007 and April 2018, the frozen elephant trunk technique was used in 282 patients. The median age was 62 years (range 18–83 years), and 233 patients were men (82.6%). Two different frozen elephant trunk prostheses were used: the Jotec E-vita open prosthesis in 167 patients (59.2%) and the Vascutek Thoraflex hybrid prosthesis in 115 patients (40.8%). Patients were divided into 2 groups according to the distal anastomosis site: zone 2 group (69 patients) and zone 3 group (213 patients). The main indications were chronic aortic dissection (n = 164, 58.2%), degenerative aneurysm (n = 72, 25.5%) and acute aortic dissections (n = 45, 16%). RESULTS The overall in-hospital mortality rate was 17%: 20% for the zone 2 group and 16% for the zone 3 group, without significant differences, also in terms of cardiopulmonary bypass and myocardial ischaemia times. However, the visceral ischaemia time was significantly shorter for the zone 2 group, whereas the antegrade selective cerebral perfusion time was significantly longer for the same group. Recurrent laryngeal nerve injury rate was lower in the zone 2 group. The overall postoperative paraplegia rate was 3.5%, whereas the occurrence of permanent neurological dysfunction and dialysis was 9% and 19%, respectively, with no significant differences between the groups. CONCLUSIONS ‘Proximalization’ of the distal anastomosis can be used for arch reconstruction, especially in complex cases such as reoperations or acute aortic dissections. Furthermore, with the aid of branched hybrid grafts, a reduction of the visceral ischaemia time is achieved.