Auditory input to the pedunculopontine nucleus: I. Evoked potentials

The pedunculopontine nucleus (PPN) has been implicated in sleep-wake control, arousal responses, and motor functions. The PPN also has been implicated in the generation of the 1311 middle-latency auditory-evoked potential. The present study was undertaken to determine the topographical distribution, threshold, and response properties of depth-recorded potentials following auditory click stimulation. Experiments were conducted in both decerebrate cat and rat, with a view towards determining the presence of P1-like middle-latency auditory-evoked potentials in the midbrain of both species. These results demonstrate a) the presence in and around the PPN of a P1-like potential in the decerebrate rat similar to that described in the accompanying article as the P13 in the intact rat; b) the presence in and around the PPN of a P1-like potential in the decerebrate cat similar to that previously described by others as wave A in the intact cat; c) although thresholds for these potentials were similar to those of intact preparations, following frequencies were higher in the decerebrate preparations, i.e., responsiveness to repetitive stimulation was higher, and d) depth-recorded somatosensory-evoked potentials also were studied in the cat and found to show an evoked potential at a similar latency as middle-latency auditory depth-recorded potentials. These findings suggest that click stimulus-evoked, depth-recorded potentials are present in and around the PPN in the decerebrate rat and cat, i.e., in the absence of cortex, at a similar latency as in intact preparations.     

Antegrade ureteral stents: technical and catheter-related problems with polyethylene and polyurethane

Antegrade placement of polyethylene and polyurethane stents was successfully achieved in 93 of 107 ureters (87 of 101 patients). These materials functioned adequately in 24 of 26 patients with indications for temporary stenting, including fistulas, strictures, and trauma caused by manipulation of calculi. Thirty of 61 patients with malignancy (49.2%) died within 6 months with their original stents in place; 12 survived to undergo elective cystoscopic stent replacement. Fifteen of the 61 patients had premature stent occlusions, which were treated by permanent nephrostomy in nine, replacement of the stent in five, and no further diversion in one patient with lymphoma. Encrustation and stent occlusion are problems during extended use of polyethylene and polyurethane stents. Long-term patency rates with newer stent materials remain to be documented and compared.     

A comparison between sinus radiographic findings and the macroscopic appearances of the para-nasal sinus mucosa

The results of a retrospective study comparing the preoperative state of the sinus mucosa with the pre-operative sinus radiographic findings are reported. In contrast to a low false-positive rate, the incidence of false-negative reporting in the ethmoidal and sphenoidal air cell systems was 43-55% and was 20% in the maxillary sinuses.     

Spontaneous perinephric and subcapsular renal hemorrhage: evaluation with CT, US, and angiography

Eighteen consecutive patients with acute spontaneous perinephric hemorrhage were examined with computed tomography (CT) (n = 18), ultrasonography (US) (n = 15), and angiography (n = 9). Renal cell carcinoma was found in 10 patients; angiomyolipoma, three; and segmental renal infarction, arteriovenous malformation (AVM), hemorrhagic cyst, abscess, and idiopathic hemorrhage, one each. Initial CT examinations demonstrated the extent of hemorrhage in all cases and a distinct mass in 12 (67%), with CT characteristics suggestive of the correct diagnosis in 11. In the other six patients (33%), a discrete mass was not seen at initial CT, and in five cause of hemorrhage was not clear. Two of the five underwent follow-up CT, which correctly demonstrated carcinoma in both. Overall, CT findings suggested the correct diagnosis in 14 patients (78%). US was sensitive for detection of an abnormality but nonspecific as to its nature. Angiography demonstrated unsuspected AVM in one patient, segmental renal infarction seen at CT in one, but only one of five carcinomas suspected at CT. Data from this study suggest that CT is the most valuable examination for patients with spontaneous renal hemorrhage.     

Prediction of fatigue failure of a total knee replacement tibial plateau using finite element analysis

Recent reports of total knee prosthesis fractures have raised concerns over the long-term structural integrity of metal-backed tibial components. Both the development of a fibrous tissue membrane under the tibial plateau of a total knee prosthesis and loading conditions may seriously alter the fatigue life of the metal tibial tray. The effects of the cement and fibrous tissue at the bone-prosthesis interface were studied. Using the method of three-dimensional finite element analysis, peak loads of normal gait were simulated at several locations on the plateau of a generic, single-stemmed, porous-coated, CoCrMo tibial component model, providing information on the effect of abnormal loading patterns. According to the analysis, stresses below the material endurance limit are predicted throughout the prosthesis prior to the development of the fibrous membrane. However, stresses exceeding the yield strength of the material are predicted in a prosthesis that is supported by a fully developed 1 mm membrane, meaning that it has a markedly increased risk of low-cycle fatigue failure. Lateral displacement of the loading is detrimental to prosthesis life because maximum stress increases 100% while posterior displacement of the loading increases maximum stress by only 30%. Anterior loading creates stresses similar to those created by central loading. Because of their susceptibility to low-cycle fatigue failure, simple, single-stemmed prostheses are not recommended in cases of questionable bone stock unless modified. Several design alternatives are proposed.     

Esophageal carcinoma with respiratory tract fistula

An experience with 27 patients with malignant respiratory tract fistula (RTF) is presented. The RTF was related to carcinoma of the thoracic esophagus in all the patients, involved the trachea in 11, left main bronchus in 7, right main bronchus in 3, and was more distal in 6 patients. Metastases were detectable in only four patients (15%) at the time of RTF diagnosis. Bronchoscopy examination in 13 patients prior to RTF development showed tracheobronchial invasion or impingement in all. The RTF was present at initial presentation in 11 patients (Group I), and developed after/during radiation therapy (RT) in 16 patients (Group II). Median survival from tumor diagnosis was 17 weeks in Group I and 37 weeks in Group II, while survival from RTF diagnosis was 16 weeks in Group I and II weeks in Group II.