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Maria Antonia Poca, Juan Sahuquillo, Thomaz Topczewski, Maria Jesús Peñarrubia and Asunción Muns

Object

Epidural pressures have been reported as being systematically higher than ventricular fluid pressures. These discrepancies have been attributed both to the characteristics of the sensor and to the particular anatomy of the epidural space. To determine which of these two possible causes better explains higher epidural readings, the authors compared pressure values obtained during simultaneous epidural and lumbar pressure monitoring in 53 patients and during simultaneous subdural and lumbar pressure monitoring in 22 patients. The same nonfluid coupled sensor device was used in all compartments.

Methods

All 75 patients had normal craniospinal communication. Simultaneous intracranial and lumbar readings were performed every 30 seconds. The epidural–lumbar and subdural–lumbar pressure values were compared using correlation analysis and the Bland–Altman method.

The median differences in initial epidural–lumbar and subdural–lumbar pressure values were 11 mm Hg (interquartile range 2–24 mm Hg) and 0 mm Hg (interquartile range −2 to 1 mm Hg), respectively. The correlation coefficients of the mean epidural–lumbar and subdural–lumbar intracranial pressure (ICP) values were ρ = 0.48 (p < 0.001) and ρ = 0.88 (p < 0.001), respectively. Using the Bland–Altman analysis, epidural–lumbar methods showed a mean difference of −20.93 mm Hg; epidural pressure values were systematically higher than lumbar values, and these discrepancies were greater with higher ICP values. Subdural–lumbar methods showed a mean difference of 0.35 mm Hg and both were equally valid with all mean ICP values.

Conclusions

Epidural ICP monitoring produces artifactually high values. These values are not related to the type of sensor used but to the specific characteristics of the epidural intracranial space.

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Alberto Di Somma, Luigi Maria Cavallo, Matteo de Notaris, Domenico Solari, Thomaz E. Topczewski, Manuel Bernal-Sprekelsen, Joaquim Enseñat, Alberto Prats-Galino and Paolo Cappabianca

OBJECTIVE

Different surgical routes have been used over the years to achieve adequate decompression of the optic nerve in its canal including, more recently, endoscopic approaches performed either through the endonasal corridor or the transorbital one. The present study aimed to detail and quantify the amount of bone removal around the optic canal, achievable via medial-to-lateral endonasal and lateral-to-medial transorbital endoscopic trajectories.

METHODS

Five human cadaveric heads (10 sides) were dissected at the Laboratory of Surgical Neuroanatomy of the University of Barcelona (Spain). The laboratory rehearsals were run as follows: 1) preliminary preoperative CT scans of each specimen, 2) anatomical endoscopic endonasal and transorbital dissections and Dextroscope-based morphometric analysis, and 3) quantitative analysis of optic canal bone removal for both endonasal and transorbital endoscopic approaches.

RESULTS

The endoscopic endonasal route permitted exposure and removal of the most inferomedial portion of the optic canal (an average of 168°), whereas the transorbital pathway allowed good control of its superolateral part (an average of 192°). Considering the total circumference of the optic canal (360°), the transorbital route enabled removal of a mean of 53.3% of bone, mainly the superolateral portion. The endonasal approach provided bone removal of a mean of 46.7% of the inferomedial aspect. This result was found to be statistically significant (p < 0.05). The morphometric analysis performed with the aid of the Dextroscope (a virtual reality environment) showed that the simulation of the transorbital trajectory may provide a shorter surgical corridor with a wider angle of approach (39.6 mm; 46.8°) compared with the simulation of the endonasal pathway (52.9 mm; 23.8°).

CONCLUSIONS

Used together, these 2 endoscopic surgical paths (endonasal and transorbital) may allow a 360° decompression of the optic nerve. To the best of the authors' knowledge, this is the first anatomical study on transorbital optic nerve decompression to show its feasibility. Further studies and, eventually, surgical case series are mandatory to confirm the effectiveness of these approaches, thereby refining the proper indications for each of them.