Carbon ions therapy as single treatment in chordoma of the sacrum. Histologic and metabolic outcome studies.

OBJECTIVE: Even though carbon ions treatment (CIRT) of sacral chordoma (SC) substantially reduces tumor mass, tumor remnants are observed in most patients. Differentiating tumor remnants from necrosis is challenging, expensive in terms of imaging and time-consuming. So far, there has not been a systematic histological and metabolic analysis of post-CIRT lesions. We designed a prospective study aiming to histologically a metabolically differentiate between viable tumor and foci of necrosis and of fibrosclerosis after CIRT and correlate these findings to clinical outcome in patients with SC. PATIENTS AND METHODS: Between January 2013 and December 2016 18 patients, 12 males and 6 females, with histological confirmation of sacral chordoma, underwent CIRT. The total dose was 70.4 GyE, with a daily fraction of 4.4 GyE, for 4 weeks. MRI was performed every three months after treatment. FDG PET-CT scan and CT-guided needle biopsy were performed 6-12 months after CIRT. The incidence of complications (intraoperative and postoperative), local control (LC), overall survival (OS) and progression-free survival (PFS), changes in neurological status, clinical outcomes and toxicity were considered. RESULTS: All histological analysis but 2 reported signs of necrosis and of fibrosclerosis after CIRT. One of these 2 patients turned into a dedifferentiated chordoma. Radiological partial response (PR) was observed in 10 patients (56.3%) and stable disease (SD) in 5 patients (28.3). Two patients (11%) had a local relapse. The overall survival rate was 100% at 24 months. FDG PET CT after CIRT showed uptake decreasing compared with the baseline exam in all but one patient. CONCLUSIONS: The histological presence of necrosis and of fibrosclerosis after CIRT at the histological analysis supports the previous clinical evidence on the efficacy of CIRT. Volumetric stability of the residual mass should be considered as a success of treatment. In cases of a volumetric increase of the mass, a CT needle biopsy should always be performed. In our series, during the follow-up, the FDG-PET was able to promptly detect an increased uptake in the case which later was histologically defined as dedifferentiated chordoma.

A systematic review: characteristics, complications and treatment of spondylodiscitis.

OBJECTIVE: This systematic review focuses on 5 key elements that may improve the decision-making process in spondylodiscitis: the infective agent, segmental instability, abscess development, neurological compromise and focus of infection. MATERIALS AND METHODS: We included 64 studies published between May 2012 and May 2017, that reported both a description of the discitis and comparative data regarding the disease and its complications. RESULTS: The majority of cases were caused by Staphylococcus spp (40.3%) and involved the lumbosacral region (52.3%). 27.8% of cases were associated to neurological compromise, 30.4% developed an abscess, 6.6% were associated to instability, and 54.7% underwent surgery. The abscesses mostly involved the lumbosacral region (60.4%) with paravertebral localization; 32.6% of cases involved the thoracic region, showing mostly epidural localization; a small number of cases (7%) involved the cervical region, mostly with epidural localization. 95% of paravertebral abscesses were treated percutaneously, while 85.7% of epidural cases underwent "open" surgery. Spinal cord compression mainly occurred in the cervical region (55.9%), neurological deficit was observed in over half of cases (65%), and surgery was required in most of the cases (83.9%). The majority of cases of instability involved the lumbosacral region (53.3%) and underwent surgery (87%). The focus of infection was mostly lumbosacral (61%) and almost all cases (95%) were treated surgically. CONCLUSIONS: Spondylodiscitis is a complex and multifactorial disease, whose diagnosis and management are still challenging. Due to its potential morbidity, it is extremely important to investigate the 5 key elements discussed in this paper in order to provide an early diagnosis and initiate the most effective treatment.

Dosimetric characterization of carbon fiber stabilization devices for post-operative particle therapy.

PURPOSE: The aim of this study was to evaluate the dosimetric impact caused by recently introduced carbon fiber reinforced polyetheretherketone (CF/PEEK) stabilization devices, in comparison with conventional titanium (Ti) implants, for post-operative particle therapy (PT). METHODS: As a first step, protons and carbon ions Spread-Out Bragg Peaks (SOBPs) were delivered to CF/PEEK and Ti screws. Transversal dose profiles were acquired with EBT3 films to evaluate beam perturbation. Effects on image quality and reconstruction artifacts were then investigated. CT scans of CF/PEEK and Ti implants were acquired according to our clinical protocol and Hounsfield Unit (HU) mean values were evaluated in three regions of interest. Implants and artifacts were then contoured in the sample CT scans, together with a target volume to simulate a spine tumor. Dose calculation accuracy was assessed by comparing optimized dose distributions with Monte Carlo simulations. In the end, the treatment plans of nine real patients (seven with CF/PEEK and two with Ti stabilization devices) were retrospectively analyzed to evaluate the dosimetric impact potentially occurring if improper management of the spine implant was carried out. RESULTS: As expected, CF/PEEK screw caused a very slight beam perturbation in comparison with Ti ones, leading to a lower degree of dose degradation in case of contouring and/or set-up uncertainties. Furthermore, CF/PEEK devices did not determine appreciable HU artifacts on CT images thus improving image quality and, as a final result, dose calculation accuracy. CONCLUSIONS: CF/PEEK spinal fixation devices resulted dosimetrically more suitable than commonly-used Ti implants for post-operative PT.

Mesenchymal Stem Cells for the Treatment of Spinal Arthrodesis: From Preclinical Research to Clinical Scenario.

The use of spinal fusion procedures has rapidly augmented over the last decades and although autogenous bone graft is the "gold standard" for these procedures, alternatives to its use have been investigated over many years. A number of emerging strategies as well as tissue engineering with mesenchymal stem cells (MSCs) have been planned to enhance spinal fusion rate. This descriptive systematic literature review summarizes the in vivo studies, dealing with the use of MSCs in spinal arthrodesis surgery and the state of the art in clinical applications. The review has yielded promising evidence supporting the use of MSCs as a cell-based therapy in spinal fusion procedures, thus representing a suitable biological approach able to reduce the high cost of osteoinductive factors as well as the high dose needed to induce bone formation. Nevertheless, despite the fact that MSCs therapy is an interesting and important opportunity of research, in this review it was detected that there are still doubts about the optimal cell concentration and delivery method as well as the ideal implantation techniques and the type of scaffolds for cell delivery. Thus, further inquiry is necessary to carefully evaluate the clinical safety and efficacy of MSCs use in spine fusion.

Best practices for the management of local-regional recurrent chordoma: a position paper by the Chordoma Global Consensus Group.

Chordomas are rare, malignant bone tumors of the skull-base and axial skeleton. Until recently, there was no consensus among experts regarding appropriate clinical management of chordoma, resulting in inconsistent care and suboptimal outcomes for many patients. To address this shortcoming, the European Society of Medical Oncology (ESMO) and the Chordoma Foundation, the global chordoma patient advocacy group, convened a multi-disciplinary group of chordoma specialists to define by consensus evidence-based best practices for the optimal approach to chordoma. In January 2015, the first recommendations of this group were published, covering the management of primary and metastatic chordomas. Additional evidence and further discussion were needed to develop recommendations about the management of local-regional failures. Thus, ESMO and CF convened a second consensus group meeting in November 2015 to address the treatment of locally relapsed chordoma. This meeting involved over 60 specialists from Europe, the United States and Japan with expertise in treatment of patients with chordoma. The consensus achieved during that meeting is the subject of the present publication and complements the recommendations of the first position paper.

Iliac crest bone graft: a 23-years hystory of infection at donor site in vertebral arthrodesis and a review of current bone substitutes.

OBJECTIVE: This is an exemplary case report underlining a relevant morbidity which could be associated to the use of autologous iliac crest bone graft (ICBG) for spine fusion. CASE REPORT: Starting from 1990, a 25-years-old woman underwent two subsequent surgical treatments for non-Hodgkin lymphoma vertebral localizations. In the second surgery, arthrodesis was obtained with autograft through right posterior iliac crest osteotomy. During the chemotherapy treatment following the surgery, the patient suffered from infection at posterior iliac crest scar, the site of previous graft, caused by methicillin-resistant Staphylococcus aureus. She was subjected to surgical debridement and specific antibiotic treatment with local healing and phlogosis index reduction. Chemotherapy protocol was concluded and the patient healed with definitive lymphoma remission. After 22 years the patient had a relapse of donor site infection, requiring a new antibiotic therapy and a new surgical debridement. RESULTS: The relapsed infection at donor site lasted for a long period, more than one year, despite of specific care. It finally healed after another accurate surgical debridement and postoperative antibiotic therapy. CONCLUSIONS: This case report underlines the possible consequences on the patient's quality of life of a long-term disease affecting the iliac crest bone graft donor site. Literature concerning alternatives to autograft for spine fusion is also reviewed.

Denosumab: non-surgical treatment option for selective arterial embolization resistant aneurysmal bone cyst of the spine and sacrum. Case report.

OBJECTIVE: Aneurysmal Bone Cyst (ABC) is a cystic lesion of bone, occurring in 70% of cases as a primary lesion. Even if the metaphyseal region of long bones is more frequently involved, vertebral localization is not rare: ABC represents 15% of all primary spine and sacral tumours. Selective arterial embolization (SAE) represents the first treatment option for vertebral ABC. However, in few cases, multiple SAEs are not possible. The aim of this work is to report two cases of vertebral ABC unresponsive to SAE positively treated with Denosumab. PATIENTS AND METHODS: Two patients affected by ABC of the lumbar spine were treated by SAE without any response. Thus, the patients were submitted to an off-label treatment with Denosumab, following the same protocol already used in case of Giant Cell Tumour (GCT): 120 mg once a week for 4 weeks consecutively, then once every 40 days. RESULTS: In both cases, patients resulted to be pain-free after 11-13 Denosumab administrations and CT scan showed almost complete ossification of the lesions. CONCLUSIONS: The two cases reported here are not conclusive but they may support the project of a prospective study to confirm the effectiveness of Denosumab in ABC treatment as an alternative to SAE.

How evolution of the nailing system improves results and reduces orthopedic complications: more than 2000 cases of trochanteric fractures treated with the Gamma Nail System.

PURPOSE: The incidence of trochanteric fractures has increased significantly during the last few decades, especially in elderly patients with osteoporosis. The dynamic/sliding hip screw and the cephalomedullary nail are the most commonly used fixation methods to treat trochanteric fractures. The improvements in the Gamma Nail System (GNS) associated with a correct surgical technique reduced the postoperative orthopedic complications. The purpose of this study was to compare the results of the different Gamma Nails. METHODS: The present study is a retrospective analysis of 2144 patients treated with GNS between January 1997 and December 2011 for trochanteric fractures, classified according to AO classification method. The patients were divided into three groups according to the nailing system: 525 were treated with Standard Gamma Nail (SGN), 422 with Trochanteric Gamma Nail (TGN) and 1197 with Gamma3 Nail. RESULTS: The overall incidence of intra-operative complications was 1.21 %; the incidence of intra-operative complications for each group was 1.71 % for SGN group, 0.47 % for TGN group and 1.25 % for Gamma3 Nail group. The overall incidence of postoperative complications was 5.48 %, and the incidence for each group was 10.73 % for SGN group, 9.92 % for TGN group and 2.92 % for Gamma3 Nail group. CONCLUSION: The GNS is a safe device with a low rate of intra-operative complications. The evolution of this nail system reduces postoperative complications, thus improving the results at follow-up and confirming that the Gamma3 Nail is a safe and predictable device to fix trochanteric fracture.

A post-market surveillance analysis of the safety of hydroxyapatite-derived products as bone graft extenders or substitutes for spine fusion.

OBJECTIVE: Iliac crest bone graft (ICBG) is considered the gold standard for spine surgical procedures to achieve a successful fusion, because of its known osteoinductive and osteoconductive properties. Considering its autogenous origin, the use of ICBG has not been associated to an increase of intraoperative or postoperative complications directly related to the surgery. However, complications related to the harvesting procedure and to the donor site morbidity have been largely reported in the literature, favoring the development of a wide range of alternative products to be used as bone graft extenders or substitutes for spine fusion. The family of ceramic-based bone grafts has been widely used and studied during the last years for spine surgical procedures in order to reduce the need for iliac crest bone grafting and the consequent morbidity associated to the harvesting procedures. PATIENTS AND METHODS: We report here the results of a post-market surveillance analysis performed on four independent cohorts of patients (115 patients) to evaluate the safety of three different formulations of hydroxyapatite-derived products used as bone graft extenders/substitutes for lumbar arthrodesis. RESULTS: No intraoperative or post-operative complications related to the use of hydroxyapatite-derived products were detected, during medium and long follow up period (minimum 12 months-maximum 5 years). CONCLUSIONS: This post-market surveillance analysis evidenced the safety of ceramic products as bone graft extenders or substitutes for spine fusion. Moreover, the evidence of the safety of hydroxyapatite-derived products allows to perform clinical studies aimed at evaluating the fusion rates and the clinical outcomes of these materials as bone graft extenders/substitutes, in order to support their use as an alternative to ICBG for spine fusion.

Polyetheretherketone (PEEK) rods: short-term results in lumbar spine degenerative disease.

Pedicle screw and rod instrumentation has become the preferred technique for performing stabilization and fusion in the surgical treatment of lumbar spine degenerative disease. Rigid fixation leads to high fusion rates but may also contribute to stress shielding and adjacent segment degeneration. Thus, the use of semirigid rods made of polyetheretherketone (PEEK) has been proposed. Although the PEEK rods biomechanical properties, such as anterior load sharing properties, have been shown, there are few clinical studies evaluating their application in the lumbar spine surgical treatment. This study examined a retrospective cohort of patients who underwent posterior lumbar fusion for degenerative disease using PEEK rods, in order to evaluate the clinical and radiological outcomes and the incidence of complications.

Less invasive surgery in idiopathic scoliosis: a case report.

BACKGROUND: Minimally invasive spine surgery (MISS) has become popular during the last decade due to continuous evidence in favor of lesser soft tissue damage, faster recovery, higher patient satisfaction and reduced health costs. During the last years, surgical ambition for better results as well as most detailed knowledge of spinal anatomy, have resulted in the continuous and successful expansion of indications of MISS, covering already successfully a wide range of degenerative spinal pathologies as well as adult spinal deformities. AIM: We describe here a case report of a patient with adolescent idiopathic scoliosis (AIS) treated by minimally invasive posterior pedicle screw instrumentation. MATERIALS AND METHODS: We report the case of an 18 years old female patient affected by AIS, Lenke type 1AN, with a 65 degree right thoracic curve and severe rib hump. Posterior pedicle screw instrumentation as well as corrective manoeuvres were performed exclusively by minimally invasive procedure, through three small midline skin incisions. RESULTS: We obtained a good clinical and radiographical correction of scoliosis, which was maintained during the follow-up period. We also observed a limited intra-operative blood loss, a limited operative time, limited pain, earlier mobilization and limited hospital stay. CONCLUSIONS: A minimally invasive technique can be used for the surgical treatment of AIS, showing satisfying deformity correction and multiple perceived advantages, although long-term data are needed before this kind of surgery can be recommended for routine use.

Myoepithelioma of the spine: first case in the literature.

Myoepithelioma is a very rare tumour. This tumor type has been reported in the soft tissue, ear, sinonasal cavity, breast and lung. Although rare, myoepithelioma can occur in bone. We present the first case of myoepithelioma in the spine, documenting the clinical, radiographic and pathological features.

Is lumbar drainage of postoperative cerebrospinal fluid fistula after spine surgery effective?

AIM: This study is a retrospective consecutive case series analysis of 198 patients who underwent spine surgery between 2009 and 2010. The aim of this paper was to assess the efficacy and safeness of bed rest and lumbar drainage in treating postoperative CSF fistula. Postoperative cerebrospinal fluid (CSF) fistula is a well-known complication in spine surgery which lead to a significant change in length of hospitalization and possible postoperative complications. Management of CSF leaks has changed little over the past 20 years with no golden standard advocated from literature. METHODS: Postoperative CSF fistulas were described in 16 of 198 patients (8%) who underwent spine surgery between 2009 and 2010. The choice of the therapeutic strategy was based on the clinical condition of the patients, taking into account the possibility to maintain the prone position continuously and the risk of morbidity due to prolonged bed rest. Six patients were treated conservatively (position prone for three weeks), ten patients were treated by positioning an external CSF lumbar drainage for ten days. The mean follow-up period was ten months. RESULTS: All patients healed their wound properly and no adverse events were recorded. Patients treated conservatively were cured in a mean period of 30 days, while patients treated with CSF drainage were cured in a mean period of 10 days. CONCLUSION: Lumbar drainage seems to be effective and safe both in preventing CSF fistula in cases of large dural tears and debilitated/irradiated patients and in treating CSF leaks.

Neuropathic pain following spinal cord injury: what we know about mechanisms, assessment and management.

BACKGROUND: In biology, it is easy to understand how a damaged functional system may generate wrong signals, but why this should happen when the system is disconnected is less clear. For this reason, among other pain syndromes, neuropathic pain (NP) following spinal cord injury (SCI) leaves most questions unanswered. AIMS AND METHODS: Our purpose is to review current knowledge on NP after SCI, focusing on the mechanisms, assessment and management of the syndrome. RESULTS: The mechanisms responsible for NP following SCI are poorly understood: NP is classically considered a "central pain syndrome" but recent evidence from experimental models reveals a possible "peripheral sensitization". Assessment of NP following SCI is well-established: in addition to clinical evaluation and self-reported scales, many neurophysiological, radiological and microscopic investigations may be performed. The management of NP following SCI is very difficult: evidence of effective drugs is lacking and alternative new treatment approaches yield different outcomes. CONCLUSIONS: Recently clinical and instrumental tools have increased our knowledge on NP, suggesting that the discovery of new treatment agents will depend on an explanation of what changes after SCI: future research must point in this direction.

The role of surgical treatment in the rehabilitation protocols of thoraco-lumbar spine injuries.

BACKGROUND: Rehabilitation is a crucial issue in the management of spinal cord injuries (SCI) but, in these patients, the primary treatment can bias the outcome of recovery protocols. AIM: Purpose of this paper is to review our case load in the treatment of surgical failures and to define the role of surgery in thoraco-lumbar injuries rehabilitation. PATIENTS AND METHODS: Between 2000 and 2009 seventy patients with post-traumatic paraplegia were referred to Surgical Department as rehabilitation was unfeasible due to inadequate spine injury treatment. Forty-six had had surgery, 24 were treated conservatively Twenty-five patients had a thoracic lesion, 9 a lumbar lesion and 36 a lesion of the thoraco-lumbar junction. A total of 44 surgical procedures were performed (by anterior, posterior or anterior-posterior). RESULTS: On postoperative imaging sagittal alignment was found good in 93% of cases and acceptable in 7%. All patients regained the sitting position within 5 days after surgery. Wound healing problems requiring revision were observed in 4 cases. Major complications were a cerebro spinal fluid (CSF) leakage and a massive pulmonary embolism case in the early post-op. CONCLUSIONS: Wrong primary treatment frequently leads to demanding revision procedures with increased risks for the patient and more than double costs for the health care system. Whatever the technique a stable spine is the target in surgery of SCI allowing a quick and effective rehabilitation without external orthosis.

Navigation-assisted surgery for tumors of the spine.

PURPOSE: Computer-assisted navigation systems are largely used for pedicle screws positioning in degenerative and traumatic spine surgery. In oncologic spine surgery its use is still developing and could be extended for tumor identification and excision. Aim of this paper is to present our experience. METHODS: Seven selected patients (5 females, 2 males), mean age 44 years (min 17-max 62) affected by primary benign or malignant tumors of the spine or spine metastases were surgically treated with the use of computer-assisted navigation system from March to October 2011. RESULTS: At 18 months mean F.U. (min 15-max 23), no LR were observed. Revision surgery was necessary only in one case for C1 pedicle screw malpositioning. CONCLUSIONS: Navigation system can improve surgical accuracy in screws placement and tumor localization and excision. Learning curve and technical aspects must be considered to avoid potential serious mistakes.

Aneurysmal bone cyst of the mobile spine: the therapeutic role of embolization.

PURPOSE: Our aim is to define the role of embolization in the treatment of aneurysmal bone cyst of the spine in order to include this option in the decision making process. METHODS: From April 2004 to November 2009, seven patients with primary aneurysmal bone cyst of the mobile spine treated by embolization have been prospectively followed-up. All clinical presentations and imagings were recorded. There are many options of embolic agent and techniques used, but all aim to devascularize the tumor. The therapeutic protocol includes: embolization repeated every 8 weeks until the appearance of radiographic signs of healing. Complications, rate of healing and clinical outcome were analyzed. RESULTS: The number of embolizations varied from one to a maximum of seven without related intra- or post-operative complications. One patient, after four selective arterial embolizations, underwent direct percutaneous injection of embolic agents into the cyst. A clinical and radiographical response was achieved in all patients who were found alive and completely free of disease at mean follow-up of 46 months after last treatment and nobody crossed to surgical option. CONCLUSION: Embolization seems to be the first option for spinal aneurysmal bone cyst treatment because of the best cost-to-benefit ratio. It is indicated in intact aneurysmal bone cyst, when diagnosis is certain, when technically feasible and safe and when no pathologic fracture or neurologic involvements are found. If embolization fails, other options for treatment would still be available.

Ewing's sarcoma of the mobile spine.

OBJECTIVES: To evaluate the role of enbloc resection on the oncological outcome of patients with Ewing's sarcoma of the mobile spine treated with systemic multiagent chemotherapy combined with radiation therapy. While the role of chemotherapy and radiation therapy is well known and accepted in the treatment of Ewing sarcoma, there is no consensus on the role of enbloc resection in those tumors occurring in the mobile spine and, therefore, it can be difficult to conclude the decision making process, particularly if to achieve a tumor-free margin resection functionally relevant structures should be sacrificed. The study design of this work was the retrospective analysis of a series of 27 cases of Ewing sarcoma of the mobile spine homogeneously treated. METHODS: Twenty-seven patients with primary ES of the mobile spine were treated from 1979 to 2008 by the same multidisciplinary team. All the patients presented with pain. Motor deficits were present in 6 patients. All the patients were submitted to multiagent protocols of chemotherapy (always) and radiotherapy (alternative to surgery or associated to). Surgery was performed in 17 cases both for functional purpose (7 cases: intralesional piecemeal excision) both for curative purpose (10 cases: enbloc resection, resulting characterized by marginal/wide or intralesional margins). Patients were observed for a minimum of 2 years or until death. The mean follow-up time was 65 months (median 28 months; ranging 2 to 218 months). Neurological function, local recurrence, distant relapse, and treatment-related complications were evaluated. RESULTS: Three periods were considered according to the evolution of therapeutic strategies. Four patients were treated in the period 1979 to 1982. All were submitted to chemotherapy (REA-2) and radiation therapy (RT). Two of them were submitted to intralesional excision. All these patients died 2 to 29 months later without significant difference in the two groups. In the period 1983 to 1990 all patients were treated with chemotherapy (REN-1/2) and RT. Two were submitted to intralesional excision and had a worse evolution as died of the disease at 2 and 11 months follow up, while the patients who did not received surgery evolved more favourably: 1 died of the disease 57 months after the end of the treatment, 3 are continuously disease free at 130, 190, 290 months. The sixteen patients treated in the period 1991 to 2008 received chemotherapy (REN-3 and ISG-SSG) and RT, combined with intralesional excision in 3, with enbloc with intralesional margins in 4, enbloc with tumor-free margins (wide or marginal) in 6. Only one patient submitted to tumor-free margin enbloc resection had local recurrence and died 29 months after the treatment (biopsy was performed by open approach), the other surviving continuously disease free at 17 to 193 months follow-up (av. 76 months). All the patients submitted to intralesional excision and to enbloc resection resulting in margin violation had the same prognosis, as died of the disease 10 to 63 months after the treatment. Only one of the 3 patients who had no surgery died of the disease 8 months after the treatment, the other surviving 9 and 49 months follow-up. Among the seven patients who had neurological symptoms at the occurrence, just those with no metastasis and who underwent enbloc resection are alive. CONCLUSIONS: The current study seems to demonstrate that tumor-free margin enbloc resection provides better local control and longer survival, while the results after intralesional margin resection or piecemeal excision combined with chemotherapy and RT is less effective than chemotherapy and RT alone.

Spinal infection multidisciplinary management project (SIMP): from diagnosis to treatment guideline.

Spine infections require a multidisciplinary approach to be treated and solved. A guide line to drive physicians in the deep complexity of such a disease is extremely helpful. SIMP suggests a flow-chart built up on clear concepts such as right and well managed antibiotic therapy, sound stability of the spine, correct and smart use of the standard and functional imaging techniques, such as f18 FDG PET/CT. In 16 months a total of 41 patients have been treated for spondylodiscitis, discitis and vertebral osteomyelitis by our team of physicians and 25 patients have been enrolled in a prospective study whose target is the assessment of the SIMP flow-chart and of every single aspect that characterize it.