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Biomedical subjects

P Pech

Publications and source records attributed to P Pech.

At least 19 recordsLinked to original sources
PubMed1996

Indirect spinal canal decompression in burst fractures treated with pedicle screw instrumentation.

STUDY DESIGN: Prospective evaluation of spinal canal areas in 67 consecutive burst fractures between T12 and L2 treated by reduction and stabilization with a pedicle fixator. OBJECTIVES: Assessment of the efficacy of "indirect" spinal canal decompression in a large series of burst fractures. SUMMARY OF BACKGROUND DATA: Up to 50% of burst fractures cause neurologic impairment. Reduction and posterior instrumentation is the most common surgical treatment. This also reduces spinal canal encroachment by indirect decompression. No consensus exists as to the consistency and adequacy of such indirect decompression. METHODS: Spinal canal areas were measured on preoperative and postoperative computed tomography scans. The degree of encroachment was compared with clinical and radiographic variables for possible correlation. RESULTS: Spinal canal encroachment was more severe among patients with neurologic deficits than among the neurologically intact. Postoperatively, mean encroachment was reduced from 35% to 12% at T12, from 37% to 17% at L1, and from 52% to 35% at L2. Loss (and postoperative restoration) of anterior vertebral height correlated best with the degree of canal encroachment (and its reduction), especially in Denis Type A burst fractures. In Denis Type B fractures, canal compromise usually was less severe and fragment reduction better in patients older than 40 years of age than in younger patients. CONCLUSIONS: Indirect decompression in burst fractures averages about half of the preexisting encroachment. Results are usually better at T12 and L1 than at L2. Additional or secondary decompression is rarely indicated if these fractures are treated early and by experienced surgeons. Burst Type B fractures in patients older versus younger than 40 years of age differ in many respects.

Adult↗
PubMed1996

Reliability of radiological measurements of the distraction gap during leg lengthening.

PURPOSE: The aim of this study was to determine the accuracy of length measurements on plain radiographs during leg lengthening and to evaluate a reliable method of measuring the amount of lengthening suitable for clinical praxis. MATERIAL AND METHODS: In an experimental study, a plastic femur was lengthened 40 mm and assessed radiographically in different positions, and the orthoradiographically calculated total length of the femur was compared with the true value. In a clinical study, 96 radiographs encompassing 14 femoral and 2 tibial lengthenings were assessed on a digitized table with a computer program (PROFILE) with regard to the amount of lengthening and the degree of magnification. RESULTS: The radiographic magnification in the experimental study, depending on position of the femur, was 17% (5-25%), and in the clinical material it averaged 16% (0-36%). CONCLUSION: Radiographs obtained with a radiopaque ruler placed at the same level as the lengthened bone allowed reliable measurements of the distraction gap.

Adolescent↗
PubMed1994

Spinal canal remodelling after stabilization of thoracolumbar burst fractures.

Spinal canal areas were measured prospectively in 22 consecutive burst fractures of the thoracolumbar junction, preoperatively, within 1 week postoperatively and 1 year after operation. Preoperative canal encroachment averaged 38% (range 10%-70%) of the estimated original area. The 11 patients with neurological impairment had a significantly more severe initial canal encroachment (mean 48%) than those who were neurologically intact (mean 33%). Postoperatively, canal encroachment had decreased to a mean of 18% (range 0%-62%). Within 12 to 15 months postoperatively, canal encroachment was further reduced by resorption of bone fragments to a mean of 2%. The largest observed remaining encroachment was 29%. The amount of bone resorption correlated significantly with the persistent postoperative encroachment. A critical appraisal of the methods used to assess the pre-fracture canal area revealed that reconstructing the vertebral foramen of the fractured vertebra on CT scans substantially overrated the original area as compared with averaging the canal area of the two adjacent vertebrae.

Adult↗
PubMed1993

CT analysis of pedicles and screw tracts after implant removal in thoracolumbar fractures.

Twenty-one burst fractures of the thoracolumbar junction were stabilized with a transpedicular fixator by surgeons experienced in this technique. Screws 5 or 6 mm in diameter were used. After the removal of the device 1 year postsurgery, axial CT scans were obtained of the instrumented vertebrae. Eighty-two pedicles were examined. In 16 pedicles, medial or lateral cortical defects were found. Five screws had intruded into the spinal canal by a maximum of 3.5 mm. In 48 pedicles a correlative comparison with the preoperative examinations was possible. Compared with the dimensions of the pedicles on the preoperative CT scans, 31 had increased in width, and 14 showed deformation indicative of fractures of the lateral pedicle wall. When the screw diameter exceeded 65% of the pedicles' outer diameter, 85% of the pedicles expanded. One of four screws had penetrated the anterior wall of the vertebra. Pedicle screw penetration on the left side above L2 poses potential risk of erosion of the aorta. The use of pedicle screws at the thoracolumbar junction by experienced surgeons carries some risk for malplacement and neurological damage. Mismatch between pedicle dimension and screw size results in pedicle expansion and lateral wall fractures, probably during screw insertion. Preoperative CT examinations should be used to help in choosing appropriate screw diameter presurgery.

Adult↗
PubMed1992

Transpedicular bone grafts misplaced into the spinal canal.

After open reduction of a burst fracture of L1, transpedicular bone grafting of the fractured vertebral body was performed. Bone grafts accidentally slipped into the spinal canal through the damaged medial wall of the pedicle. No adverse effects were noted clinically, but this case illustrates that transpedicular bone grafting is a potentially dangerous procedure. Computed tomography after 1 year showed complete resorption of the intraspinal bone grafts.

Bone Transplantation↗
PubMed1992

Biotransformation of diethenylbenzenes. III: Identification of metabolites of 1,3-diethenylbenzene in rat.

1. Biotransformation of 1,3-diethenylbenzene (1) in rat gave four major metabolites, namely, 3-ethenylphenylglyoxylic acid (2), 3-ethenylmandelic acid (3), N-acetyl-S-[2-(3-ethenylphenyl)-2-hydroxyethyl]-L-cysteine (4) and N-acetyl-S-[1-(3-ethenylphenyl)-2-hydroxyethyl]-L-cysteine (5) were isolated from urine and identified by n.m.r. and mass spectrometry. 2. Four minor metabolites, 3-ethenylbenzoic acid (6), 3-ethenylphenylacetic acid (7), 3-ethenylbenzoylglycine (8) and 2-(3-ethenylphenyl)ethanol (9) were identified by g.l.c.-mass spectrometric analysis of urine extract derivatized in two different ways. 3. All identified metabolites are derived from 3-ethenylphenyloxirane (10), a reactive metabolic intermediate. No product of any metabolic transformation of second ethenyl group has been identified. However, several minor unidentified metabolites were detected by g.l.c.-mass spectrometry. 4. Total thioether excretion in 24 h urine after a single i.p. dose of 1 amounted to 28.3 +/- 3.5 dose (mean +/- SD). No significant differences in the thioether fraction were observed in the dose range 100-300 mg/kg. 5. Thioether metabolites consisted mainly of mercapturic acids 4 and 5. The ratio of metabolites 5 to 4 was 62:38. Each mercapturic acid consisted of two diastereomers. Their ratio, as determined by quantitative 13C-n.m.r. measurement was 95:5 and 79:21 for mercapturic acids 4 and 5, respectively.

Animals↗
PubMed1989

Biotransformation of diethenylbenzenes. I. Identification of the main urinary metabolites of 1,4-diethenylbenzene in the rat.

1. Biotransformation of 1,4-diethenylbenzene (1) in rat was studied. Six urinary metabolites, namely, N-acetyl-S-[2-(4-ethenylphenyl)-2-hydroxyethyl]-L-cysteine (3), N-acetyl-S-[1-(4-ethenylphenyl)-2-hydroxyethyl]-L-cysteine (4), N-acetyl-S-[1-(4-formylphenyl)-2-hydroxyethyl]-L-cysteine (5), 1-(4-ethenylphenyl)ethane-1,2-diol (6), 4-ethenylbenzoic acid (9) and 4-ethenylbenzoyl-glycine (12) were isolated and identified by n.m.r. and mass spectrometry. 2. G.l.c.-mass spectral analysis of the methylated urine extract allowed the identification of four other metabolites, as 4-ethenylphenylacetic acid (11), 4-ethenylphenylacetylglycine (13), 4-ethenylmandelic acid (7), and 4-ethenylphenylglyoxylic acid (8). 3. The structures of the identified metabolites indicate that the main reactive intermediate in the metabolism of 1 is 4-ethenylphenyloxirane (2). The first step in the biotransformation of 1, formation of an oxirane, is very similar to the metabolic activation of styrene. However, subsequent steps lead not only to analogues of styrene metabolites but also to oxidation of the second ethenyl group leading to compound(s) which may contribute to the toxicity of 1, e.g. to the aldehyde 5. 4. Rats dosed with a single i.p. dose of 1 excreted nearly 5.6% of the dose as the glycine conjugate 12, irrespective of the dose. 5. In contrast, the total thioether fraction decreased significantly with increasing dose, being 23 +/- 3, 17 +/- 5 and 12 +/- 1% of dose at 100, 200 and 300 mg/kg, respectively (mean +/- SD).

Animals↗
PubMed1988

The effect of patient positioning on MR imaging of the internal auditory canal.

Identification of individual cranial nerves and complete exclusion of tumor in the internal auditory canal may be difficult with MR, especially in imperfectly positioned patients. MR studies of the temporal bones in patients and in normal volunteers positioned non-rotated or canted were correlated with corresponding cryomicrotomic sections. Especially in axial images, oblique sectioning of cranial nerves VII and VIII may cause difficulty in identifying individual nerves. A combination of axial and coronal short TR and TE images can be used to confidently exclude intracanalicular tumor in most cases.

Facial Nerve↗
PubMed1988

Cervical neural foramina: correlative anatomic and MR imaging study.

Accurate diagnosis of diseases affecting the cervical neural foramina with magnetic resonance (MR) imaging requires an appreciation of the normal anatomic appearance of the foramen. The MR appearance of the foramen was studied in cadavers and healthy volunteers and was correlated with cadaver cryomicrotome sections. With gradient-echo techniques, foraminal soft tissues are highlighted relative to adjacent bone, making gradient-echo images valuable for evaluating the overall size and contents of the neural foramina. Intravenously administered gadolinium DTPA produces enhancement of all foraminal soft tissues, including the dorsal root ganglion. The nerve roots do not enhance with Gd-DTPA. Gradient-echo pulse sequences and intravenous use of Gd-DTPA represent promising techniques for the evaluation of the cervical foramina.

Cervical Vertebrae↗
PubMed1988

MR imaging of the cavernous sinus: value of spin echo and gradient recalled echo images.

A detailed evaluation of the MR appearance of the pituitary gland-cavernous sinus junction has not been described. In a series of coronal T1-weighted spin echo images without and with IV gadolinium, we noted the variable size and signal intensity of cavernous venous spaces adjacent to the pituitary gland and the inconsistent visualization of the dural membrane just lateral to the gland. Correlation of coronal T1-weighted spin echo and gradient recalled echo images (the latter with high-signal-intensity vascular structures) proved to be an effective means of identifying cavernous venous spaces, connective tissue and cranial nerves, and the lateral margins of the pituitary gland, and of differentiating tumor tissue from cavernous venous spaces. Further work is needed to develop criteria to distinguish cavernous sinus compression from actual tumor invasion.

Adenoma↗
PubMed1988

Correlative investigations of craniospinal anatomy and pathology with computed tomography, magnetic resonance imaging and cryomicrotomy.

A correlative computed tomographic-anatomic method was applied to multiplanar anatomic studies. The method was particularly valuable for comparative anatomic investigations of complex regions of the central nervous system. The description of CT and MR anatomy in this thesis is based either on direct CT-anatomic correlation of the same specimen, or on indirect MR-anatomic correlation with cryosectional images from cadavers. In sagittal partial saturation MR images with short repetition times, the pituitary fossa in 41 normal volunteers appeared inhomogeneous. A postero-inferiorly located high intensity signal correlated with an intrasellar fat pad in sagittal cryosectional images. The height of the pituitary gland in 38 normal volunteers was usually less than 8 mm and its upper surface was flat or concave. The cavernous sinus anatomy was studied in coronal and axial MR planes in seven normal volunteers and 15 patients in correlation with cryosectional images. The intracavernous cranial nerves were best shown in the coronal plane, in partial saturation and inversion recovery sequences and displayed as foci of high signals intensity. MR signs of a parasellar mass included obliteration of intracavernous venous spaces, displacement of the intracavernous portion of the internal carotid artery and bulging of the lateral wall of the cavernous sinus. The topographic anatomy of the cervical neuroforamina was investigated in axial, sagittal, coronal and oblique planes in a correlative CT-anatomic investigation in 19 specimens. In four normal volunteers, the surface coil MR images of the cervical neuroforamina were correlated with cryosectional images. Surface coil MR images in a plane perpendicular to the cervical nerve roots allowed to determine their relationship to intraforaminal structures and the boundaries of the foramen. The dorsal and ventral nerve roots were demonstrated with both CT and MRI. They were located in the lower half of the foramen at and below the intervertebral disc space. The dorsal nerve roots were in contact with the superior articular process. The ventral nerve roots abutted the uncinate process and the inferior portion of the foramen. In a biomechanical cervical spinal trauma study, experimental fractures were studied with CT in axial and sagittal planes. Sagittal anatomic images showed the fractures and soft tissue injuries. Non-displaced and horizontal fractures were generally difficult to detect on axial CT scans alone. In two pathologic spine specimens CT scans in axial, sagittal and coronal planes were compared with reformatted scans and cryosectional images. Direct CT images revealed four cervical spinal fractures whereas the reformatted images only showed one displaced pedicle fracture.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Hippocampal formation and related structures of the limbic lobe: anatomic-MR correlation. Part II. Sagittal sections.

Magnetic resonance (MR) images in the sagittal plane display the lengths of the parahippocampal gyrus, subiculum, dentate gyrus, hippocampus, fimbria, fornix, hippocampal fissure, choroidal fissure, and temporal horn, and the anatomic relationships of these structures to the surrounding brain. Correlation of these images with anatomic specimens provides criteria for identifying these structures confidently on routine clinical MR imaging.

Hippocampus↗
PubMed1987

Computed tomography and magnetic resonance imaging of the orbital apex.

This article describes the CT and MR appearance of the orbital apex and masses in this region. The sectional anatomy by axial, coronal, and sagittal planes as well as the thin-layer technique used to accomplish this is detailed first. Then the application of these techniques to the presence of tumors is illustrated and discussed.

Humans↗
PubMed1986

Experimental endovascular reinforcement.

Techniques to reinforce a vessel wall without occluding its lumen are being studied. In pilot experiments the intimal surface along a short segment of vein was coated with plastic by injecting liquid silicone rubber into a vessel, spreading the material along the vessel with a balloon catheter, allowing polymerization and then removing the catheter. In 17 experiments in the iliac vein of rabbits, successful coating was obtained in 5. If perfected, these techniques might be applicable to treating some aneurysms or arteriosclerotic plaques.

Angioplasty, Balloon↗
PubMed1986

Experimental spinal injuries with vertical impact.

Fifteen fresh, intact, human male cadavers suspended head down were dropped vertically from a height of 0.9-1.5 meters. In eight specimens the heads were restrained to simulate muscle forces. The head-neck complex was oriented for maximal axial loading of the cervical and upper thoracic spine. In several cadavers, load cells were placed in cervical bodies. Head impact forces of 3,000-7,000 N in the unrestrained, and 9,800-14,600 N in the restrained, cadavers were recorded. There were more cervical and upper thoracic fractures in the restrained cadavers than in the nonrestrained subjects. The biomechanic and pathologic findings, including results of cryomicrotomography and computed tomography (CT), are discussed.

Aged↗
PubMed1986

Anterior commissure: anatomic-MR correlation and use as a landmark in three orthogonal planes.

Correlation of cryomicrotomic and myelin-stained sections of human cadaver heads with spin-echo magnetic resonance (MR) images documents that MR imaging routinely displays the anterior commissure in three orthogonal planes as a distinct white-matter tract that resembles bicycle handlebars. The anterior commissure crosses the midline at the upper end of the lamina terminalis, just anterior to the anterior columns of the fornices. To each side of midline, it curves antero-inferolaterally and then postero-inferolaterally through the lateral nucleus of the globus pallidus to course with the white matter of the external and extreme capsules toward the middle and inferior temporal gyri. Because the anterior commissure is easily recognizable in all three planes at differing pulse sequences, the commissure has proved to be a major landmark for identification of the complex anatomy of this region, especially in sagittal sections.

Brain↗