Physiologic Mechanisms of Water and Electrolyte Disturbances After Transsphenoidal Pituitary Surgery.

BACKGROUND: Disturbances in water and electrolyte homeostasis are common after transsphenoidal surgery. These disorders are variable and unpredictable, increasing patient risk and complicating postsurgical treatment. Clinically, it is generally accepted that damage to the pituitary is the cause, but the mechanisms behind the response variability and underlying pathophysiology remain unknown. OBJECTIVE: To test the hypothesis that changing the degree of damage to the pituitary stalk produces a spectrum of water and electrolyte disturbance along which all presentations of postsurgical water and electrolyte disturbances can be identified. METHODS: We used HumMod, a large mathematical model of physiology, to simulate pituitary stalk damage at differing fractions: 20%, 40%, 60%, and 80%. The damaged neurons were modeled to undergo a 5-day countdown to degeneration and release stored antidiuretic hormone as they die, as is proposed to occur. RESULTS: Lower pituitary damage (20%) resulted in transient polyuria and intermediate damage (40%) was associated with delayed polyuria and diabetes insipidus. Higher levels of damage (60% and 80%) showed a triphasic pattern of diabetes insipidus. CONCLUSIONS: We postulate that our model provides a plausible mechanistic explanation for some varieties of postsurgical water and electrolyte disturbances, in which increasing damage to the pituitary potentiates the likelihood of a full triphasic response. However, our simulation shows that merely modifying the level of damage does not produce every presentation of water and electrolyte imbalance. This theory suggests that other mechanisms, which are still unclear and not a part of this model, may be responsible for postoperative hyponatremia and require further investigation.

A novel simulation model for minimally invasive spine surgery.

OBJECTIVE: Minimally invasive spine surgery (MISS) is among the fastest growing technologies in general neurosurgical practice. In addition, great demand exists to teach these skills to neurosurgery residents. With newly enforced work hour restrictions, opportunities to acquire these skills are limited, necessitating development of alternative strategies of education. We describe a novel simulation model for MISS supplemented by resident self-assessment analysis and evaluation. METHODS: The simulator was constructed using a nontransparent Plexiglas frame supplemented with a modified halo frame on which to affix spine specimens. Interchangeable copper tubing was affixed to a 360-degree pivot system to replicate a working portal. Deer skulls and spines were then collected and prepared accordingly. Laboratory exercises were based on the resident's level of training with emphasis on proper drilling techniques. Eight neurosurgery residents were asked to complete the exercises and complete a self-assessment survey regarding their competence level on a scale of 0 to 5, both before and after completing the skill sets. Additionally, they were asked to complete an exit survey that was used to assess the simulation exercises. RESULTS: All exercises were completed successfully with the exception of placing 2 separate pedicle screws through the same portal, which posed difficulty on some specimens because of the of lack of lordosis of the specimens, leading to unfavorable trajectories using a free-hand technique. With regard to the resident self-assessment analysis, the mean confidence rating for performing an MISS laminectomy improved by a difference of 1.25 points (n = 8; 95% confidence interval, 0.66-1.84; P = 0.0015), from 2.50 to 3.75 before and after simulation exercises, respectively, and reached statistical significance. For the senior-level residents, the mean confidence rating for performing MISS placement of pedicle screws using a free-hand technique improved by a difference of 1.00 (n = 3; 95% confidence interval, -1.48-3.48; P = 0.225), from 3.33 to 4.33 before and after simulation exercises, respectively. Results of the exit survey were encouraging. CONCLUSION: The MISS simulator is a feasible, inexpensive, and reproducible adjunct to neurosurgery resident training and provides a new teaching method for spine surgery. Further investigation of this technology is warranted, although multicenter, randomized, controlled trials assessing its validity may not be practical because of ethical constraints with regard to patient safety.

Percutaneous placement of an external drain of the cisterna magna using interventional magnetic resonance imaging in a patient with a persistent cerebrospinal fluid fistula: technical case report.

OBJECTIVE: Cerebrospinal fluid diversion from the cisterna magna has been described previously but has largely been abandoned because of high complication rates and anatomic constraints. Situations still remain in which this may be the best or only alternative. We describe the use of interventional magnetic resonance imaging (iMRI) for the application of this largely forgotten procedure. PRESENTATION: A 28-year-old woman with a previously diagnosed malignant peripheral nerve sheath tumor of the thoracic spine presented with a refractory postoperative cerebrospinal fluid leak complicated by diffuse meningeal carcinomatosis. External lumbar drainage was unsuccessful because of complete tumor obliteration. An attempt at primary closure augmented with muscle flaps was also ineffective. Ventricular drainage was deferred because of concern for tumor seeding, thus necessitating a more aggressive approach. TECHNIQUE: The patient was intubated and placed in the open iMRI portal in a lateral decubitus position. Under direct image guidance, a closed-tip lumbar catheter was inserted into the cisterna magna through an iMRI-compatible biopsy needle and then connected for external drainage. CONCLUSION: To our knowledge, this is the first described use of iMRI technology for catheterization of the cisterna magna for cerebrospinal fluid diversion. Moreover, iMRI technology should be considered in future applications of complex posterior fossa shunting procedures.

A clinician's view of spinal cord injury.

The primary cause of spinal cord injury (SCI) is automobile collisions, followed by violence, falls, and injuries in sporting events. The patient is most frequently a young male. Regardless of cause and age, SCI is a potentially catastrophic injury. The unique anatomical relationship of the spinal cord, being enclosed in the dural sac within the bony vertebral column, make it venerable to a wide range of traumatic insults. SCI is classified as complete or incomplete with several subclasses arranged under each of these respective headings. The probability of recovery to a functional state is usually better for patients with incomplete injuries. Treatment for SCI involves initially immobilizing the injured vertebral column, medications to prevent secondary injury, and potential surgery to release pressure on the spinal cord and restore stability to the vertebral column. Postsurgical care is directed toward prevention and treatment of secondary complications of SCI such as respiratory failure, deep venous thrombosis, and decubitus ulcers. Advances in these areas are providing patients with a greater probability of recovery, a longer life, and a better quality of life. Research in the clinical and basic sciences is opening new avenues of hope for the spinal cord injury patient.