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Giampietro Pinna, Franco Alessandrini, Alex Alfieri, Marcella Rossi and Albino Bricolo

Cerebrospinal fluid (CSF) flow abnormalities are known to be present in Chiari I malformation and to underlie the origin and progression of associated syringomyelia. The incidence of syrinx formation, however, is variable for unknown reasons. The aim of this study was to investigate whether differences in CSF flow dynamics in patients with Chiari I malformation may account for the different clinical and radiological presentation.

Presurgical and postsurgical phase-contrast magnetic resonance imaging investigations were prospectively conducted in 47 adult patients with symptomatic Chiari I malformation. Patients were divided into two groups according to the presence (32 cases) or absence (15 cases) of syrinx. Cerebrospinal fluid flow patterns were evaluated at four regions of interest: prebulbar cistern, foramen magnum, and the ventral and dorsal spinal subarachnoid spaces at the C-5 level. A temporal analysis of CSF flow waveforms was performed with measurement of cranial- and caudal-directed flow durations. All patients underwent a craniocervical decompressive procedure. Preoperatively, a prolonged caudal-directed (systolic) flow pattern was observed in patients with syringomyelia, as compared with normal control values obtained in 15 healthy volunteers. Conversely, a decreased systolic duration was observed in Chiari I patients who had malformation without syrinx. These trends were not statistically significant because of the considerable degree of overlap with the control values recorded in both groups. Additional comparison of the observed preoperative values obtained in patients with and those without syringomyelia indicated that the difference in systolic flow duration was significant at the ventral spinal subarachnoid space level (p = 0.003) and remarkable at the other levels, although not reaching statistical significance. Cerebrospinal fluid flow was minimal or absent at the foramen magnum (dorsal aspect) due to tonsillar herniation, precluding reliable quantitative measurement at this level. There was no evidence of communication between the fourth ventricle and syrinx in any case. Postoperatively, unobstructed CSF flow was recorded across the enlarged foramen magnum and into the artificial cisterna magna in all patients. A gradual restoration of near-normal flow patterns was observed in both groups. Inside the syrinx, fluid motion gradually tapered, no longer being detectable in 12 patients (37.5%) 1 year postsurgery.

In patients with Chiari I malformation and associated syringomyelia different CSF flow patterns were demonstrated as compared with patients in whom syrinx was absent. Analysis of this study's findings supports the hypothesis that in Chiari I malformation an elongated systolic flow may prolong the condition of increased spinal subarachnoid pressure caused by the junctional obstruction, thus favoring CSF penetration into the spinal cord. It may be also proposed that a shortened systolic flow may be insufficient to maintain a hypertensive condition for enough time to induce syrinx formation.

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Roberto Gazzeri, Marcelo Galarza, Massimiliano Neroni, Claudio Fiore, Andrea Faiola, Fabrizio Puzzilli, Giorgio Callovini and Alex Alfieri

OBJECT

Spacers placed between the lumbar spinous processes represent a promising surgical treatment alternative for a variety of spinal pathologies. They provide an unloading distractive force to the stenotic motion segment, restoring foraminal height, and have the potential to relieve symptoms of degenerative disc disease. The authors performed a retrospective, multicenter nonrandomized study consisting of 1108 patients to evaluate implant survival and failure modes after the implantation of 8 different interspinous process devices (IPDs).

METHODS

The medical records of patients who had undergone placement of an IPD were retrospectively evaluated, and demographic information, diagnosis, and preoperative pain levels were recorded. Preoperative and postoperative clinical assessments in the patients were based on the visual analog scale. A minimum of 3 years after IPD placement, information on long-term outcomes was obtained from additional follow-up or from patient medical and radiological records.

RESULTS

One thousand one hundred eight patients affected by symptomatic 1- or 2-level segmental lumbar spine degenerative disease underwent placement of an IPD. The complication rate was 7.8%. There were 27 fractures of the spinous process and 23 dura mater tears with CSF leakage. The ultimate failure rate requiring additional surgery was 9.6%. The reasons for revision, which always involved removal of the original implant, were acute worsening of low-back pain or lack of improvement (45 cases), recurrence of symptoms after an initial good outcome (42 cases), and implant dislocation (20 cases).

CONCLUSIONS

The IPD is not a substitute for a more invasive 3-column fusion procedure in cases of major instability and spondylolisthesis. Overdistraction, poor bone density, and poor patient selection may all be factors in the development of complications. Preoperatively, careful attention should be paid to bone density, appropriate implant size, and optimal patient selection.

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Julian Prell, Jens Rachinger, Robert Smaczny, Bettina-Maria Taute, Stefan Rampp, Joerg Illert, Gershom Koman, Christian Marquart, Alexandra Rachinger, Sebastian Simmermacher, Alex Alfieri, Christian Scheller and Christian Strauss

Object

The incidence of deep venous thrombosis (DVT) after craniotomy is reported to be as high as 50%. In outpatients, D-dimer levels of more than 0.5 mg/L indicate venous thromboembolism (VTE, which subsumes DVT and pulmonary embolism [PE]) with a sensitivity of 99.4% and a specificity of 38.2%. However, D-dimer levels are believed to be unreliable in postoperative patients. The authors undertook the present study to test the hypothesis that D-dimer levels would be systematically raised in a postoperative population and to define a feasible threshold for identification of VTE.

Methods

Doppler ultrasonography of the lower extremity was performed pre- and postoperatively to evaluate for DVT in 101 patients who underwent elective craniotomy. D-dimer levels were assessed preoperatively and on the 3rd, 7th, and 10th days after surgery. Statistical analysis was carried out to define a feasible threshold for D-dimer levels.

Results

D-dimer plasma levels were found to be systematically raised postoperatively, and they differed between patients with and without VTE in a highly significant way. On the 3rd day after surgery, D-dimer levels of more than 2 mg/L indicated VTE with a sensitivity of 95.3% and a specificity of 74.1%, allowing for the definition of a feasible threshold. D-dimer levels of more than 4 mg/L were observed in all patients who had PE during the postoperative period (n = 9). Ventilation time and duration of surgery were identified as highly significant risk factors for the development of VTE.

Conclusions

Using a threshold of 2 mg/L, D-dimer levels will indicate VTE with a high degree of sensitivity and specificity in patients who have undergone craniotomy. Pulmonary embolism seems to be indicated by even higher D-dimer levels. Given that the development of D-dimer plasma levels in the postoperative period follows a principle that can be predicted and that deviations from it indicate VTE, this principle might be applicable to other types of surgery.