Surgical approaches to diseases of the orbital apex.

The authors report their experience with transcranial approaches to the orbit in situations where adequate exposure would not have been obtained with the usual orbital techniques. In addition to the standard frontal craniotomy, a supraorbital transcranial approach is described that involves removal of the superior rim and roof of the orbit, allowing exposure of all but the floor of the orbit. The main indication for this technique is a mass deep in the orbital apex that would be difficult or impossible to expose with a conventional orbitotomy. Seven representative cases are presented that illustrate conditions falling in that category.

Experimental dysraphism in the rat.

An experimental treatment that results in dysraphic lesions in rat embryos was studied to gain insight into the origin of such lesions. Pregnant rats given 100,000 units of vitamin A by gavage tube on gestational Days 8, 9, and 10 produced abnormal litters, and 50% of the embryos had exencephaly and/or spina bifida. Study of these embryonic lesions revealed hyperplesia of neural tube tissue that extended laterally to the edge of an epidermal defect. The epidermal defect consisted of the absence of fetal epidermis over the hyperplastic neural tissue. At no stage in development was embryonic hydrocephalus noted. In fact, the central canals of the embryos with malformations were poorly developed and smaller than those of control embryos. Results with this model indicate that the malformations arise through a process of overgrowth and hyperplasia and not from embryonic hydrocephalus. Continued work with this and other models is required to delineate new mechanisms and to offer alternative postulates for the origin of dysraphic lesions.

Transthoracic approach for Pott's disease.

Spinal tuberculosis with paraplegia, although decreasing in incidence, remains a problem in certain sections of the United States and in most underdeveloped nations. Evacuations of the tuberculous abscess, debridement of necrotic bone, and fusion of the anterior spine are maneuvers performed increasingly by thoracic surgeons. Twenty-two patients with Pott's disease and symptoms of back pain, gibbous deformity, and neurological deficit underwent thoracotomy. Nine were paraplegic prior to operation. Postoperatively, spinal fusion occurred in all cases. All paraplegic patients can walk now, and 17 of the 22 treated operatively have been completely rehabilitated and are in school or working. The average hospital stay was 2.4 months. There was 1 operative death. Medical treatment for Pott's disease consisted of bed rest and chemotherapy and resulted in progressive neurological deficit in 2 patients with an average hospital stay of 2.2 years. We believe operative treatment offers two distinct advantages: excellent reversal of even long-standing paraplegia and markedly shortened hospital stay.

Chronic measurement of epidural pressure with an induction-powered oscillator transducer.

An induction-powered oscillator transducer (IPOT) was designed for the chronic measurement of epidural pressure. The transducer was completely implantable so all pressure measurements were made through the intact skin. The IPOT had a linear pressure range from -50 to +200 cm H2O, was sensitive to 1 mm H2O and had a zero drift of less than 1 mm H2O/day under full load. Zero drift was minimized by using a hermetically-sealed metal bellows transducing element which was chemically treated to prevent corrosion and creep. The correlation between epidural pressure and intraventricular pressure was determined during the first 24 hours after implantation in six dogs. Epidural pressure was found to be a linear function of intraventricular fluid pressure. Epidural pressure and intraventricular pressure were essential equal provided the epidural wedge pressure was minimized by proper insertion of the transducer. The correlation between epidural pressure and intraventricular pressure was determined after chronic implantation in five dogs. Epidural pressure was a linear function of intraventricular pressure in the chronically implanted dogs, but epidural pressure was not equal to intraventricular pressure. After chronic implantation, the epidural pressure transducer was not responsive to changes in intraventricular pressure because of mechanical changes in the dura. The dura became stiff and non-compliant. Maximum correlation between epidural pressure and intraventricular fluid pressure in chronic implantations will depend on judicious material selection and mechanical design at the transducer-dura interface.