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Biomedical subjects

A L Weber

Publications and source records attributed to A L Weber.

At least 55 records · Page 3Linked to original sources
PubMed1994

Chordomas of the skull base. Radiologic and clinical evaluation.

Chordomas are uncommon skull base tumors, which are locally agressive and are usually not amenable to complete surgical resection. Proton beam irradiation, following surgery, is the preferred treatment modality. For diagnosis and determination of tumor site and extension, CT and MR imaging are the imaging modalities of choice. CT delineates bone destruction and the presence of calcifications and destroyed bone optimally. MR imaging is the modality of choice for better definition of the tumor margin from brain and other soft tissue structures (pharynx) and visualization of blood vessels. The signal intensities and enhancement pattern fail to differentiate chordoma from chondroid chordoma or chondrosarcoma. Chordomas arise from the clivus and therefore are located more centrally, whereas the majority of chondrosarcomas originate in the petroclival fissure and occur more laterally, although occasional overlap occurs in about one third of cases. Immunohistochemical methods allow differentiation of pure chordoma from chondroid chordoma and chondrosarcoma. Chordomas have a lower local control rate than chondrosarcomas.

Adult↗
PubMed1994

Chondrosarcoma of the skull base.

Chondrosarcomas are relatively rare tumors of the skull base. This article surveys the clinical and pathologic features of these lesions. In recent years there have been remarkable advances in both the imaging and treatment of these lesions. Both CT scanning and MR imaging are usually necessary for the complete evaluation of these tumors because of the involvement of both soft tissue and bony structures at the skull base. New surgical techniques and the use of high-energy proton beam irradiation have improved the prognosis for patients with these lesions.

Adult↗
PubMed1994

Radiologic evaluation of the jugular foramen. Anatomy, vascular variants, anomalies, and tumors.

The jugular foramen varies considerably in size and shape, along with the jugular vein. The foramen is traversed by several vessels and nerves. CT, in various section planes, demonstrates the bone anatomy optimally, whereas MR (including MR angiography) reveals the vascular and soft tissue structures to best advantage. A diverse group of vascular anomalies originate in the foramen and adjacent carotid canal that must be differentiated from tumors. The most common tumor within the jugular foramen is the hypervascular glomus jugulare tumor followed by neurogenic tumors, predominantly the schwannoma. Less common lesions comprise meningioma, hemangiopericytoma, chondrosarcoma, and plasmacytoma. Metastases and malignant tumors arising in adjacent anatomic structures (nasopharynx, parotid, and temporal bone), in advanced stages, may spread to the jugular foramen. Endolymphatic sac tumors arise at the posterior medial aspect of the petrous bone and frequently extend to the jugular foramen. Irregular lytic bone destruction, with enlargement and hypervascularity, demonstrated by CT and MR imaging, are characteristic for glomus jugulare tumors. Benign tumors, most commonly the jugular foramen schwannoma, display an enlarged jugular foramen with well-defined bone margins.

Bone Diseases↗
PubMed1993

Idiopathic laryngotracheal stenosis: radiologic findings.

OBJECTIVE: Acquired nonneoplastic laryngotracheal stenosis can be either focal or diffuse. Diffuse tracheal stenosis is caused by sarcoidosis, tuberculosis, histoplasmosis, relapsing polychondritis, tracheopathia osteoplastica, and Wegener's granulomatosis. Focal tracheal stenosis, on the other hand, usually results from placement of an endotracheal or tracheostomy tube or from previous neck trauma. At our institution, since 1971, we have seen 49 cases of focal laryngotracheal stenosis that could not be attributed clinically or histologically to any one of the aforementioned causes. The purpose of this study was to study the radiologic features of these idiopathic laryngotracheal stenoses. MATERIALS AND METHODS: A retrospective review of records showed that radiologic studies were still available in only 15 of the 49 patients with idiopathic laryngotracheal stenoses. All 15 patients had radiographs and plain tomograms, and one patient had a CT scan of the neck. Three radiologists reviewed all the images. RESULTS: The radiologic appearance was variable: the stenoses were from 2 to 4 cm long with a lumen between 3 and 5 mm in diameter at the narrowest portion. The narrowing was concentric and shaped like an hourglass in eight patients (53%) and was eccentric in the other seven (47%). The margins of the stenosis were smooth in nine patients (60%) and irregular and lobulated in six patients (40%). A dominant mass measuring approximately 1 cm in diameter was present in two patients (13%). No evidence of calcification or ossification was seen. CONCLUSION: Idiopathic laryngotracheal stenosis produces focal stenosis of the cervical part of the trachea, 2 to 4 cm long. The lumen is severely compromised, measuring no more than 5 mm in diameter at its narrowest portion. The stenosis can be concentric or eccentric and can have either smooth or lobulated margins. Special attention should be paid to the airways when chest radiographs of patients with a history of prolonged dyspnea and wheezing are reviewed. The prevalence of focal stenosis of the larynx and the upper part of the trachea due to tracheal intubation has declined since the introduction of low-pressure, high-volume retention cuffs. Therefore, idiopathic laryngotracheal stenosis should be considered in the differential diagnosis in patients with focal narrowing of the airway.

Adolescent↗
PubMed1993

Imaging of cysts and odontogenic tumors of the jaw. Definition and classification.

For the evaluation of jaw cysts and odontogenic tumors, the radiologic examinations include conventional films, computed tomographic (CT) scans, and magnetic resonance (MR) images. The indications for these radiologic methods are discussed along with the radiologic findings for the various cysts and tumors described. The differential diagnosis of these lesions is also included in the discussion.

Cysts↗
PubMed1992

Prebiotic sugar synthesis: hexose and hydroxy acid synthesis from glyceraldehyde catalyzed by iron(III) hydroxide oxide.

Iron(III) hydroxide oxide [Fe(OH)O] efficiently catalyzed the condensation of 25 mM DL-glyceraldehyde to ketohexoses at 25 degrees C (pH 5-6). At 16 days the yields were sorbose (15.2%), fructose (12.9%), psicose (6.1%), tagatose (5.6%), and dendroketose (2.5%) with 19.6% of triose unreacted. Analysis at 96 days showed no decomposition of hexoses. Under these conditions Fe(OH)O also catalyzed the isomerization and rearrangement of glyceraldehyde to dihydroxyacetone and lactic acid, respectively. In these reactions, about 10% of the glyceraldehyde was oxidized to glyceric acid with concurrent reduction of the iron(III) to iron(II). The partial reduction of Fe(OH)O did not noticeably reduce its ability to catalyze hexose synthesis. The relationship of these results to prebiotic sugar synthesis is discussed.

Carbohydrates↗
PubMed1992

Imaging of the salivary glands.

Salivary gland diseases are very common disorders and require radiologic evaluation. Several radiologic methods are used for assessment of these diseases. Conventional films of the parotid and submandibular glands demonstrate opaque stones in the duct system, whereas sialography depicts nonopaque stones, provides additional information on the position of the stones, and differentiates it from other calcific densities near the duct system, as well as providing information concerning ectasia of the ducts. CT has been used for evaluating mass lesions and extraglandular inflammatory disease, including abscesses. CT also depicts stones that may not be visible on conventional films. MR imaging has become an important modality in the diagnosis and definition of benign and malignant tumors and cysts and it will probably replace CT as the primary imaging modality for the assessment of these lesions. Gadolinium may be used in the examination, especially if a malignant tumor is suspected (because of irregularity and intraglandular extension).

AIDS-Related Complex↗
PubMed1991

Origin of fatty acid synthesis: thermodynamics and kinetics of reaction pathways.

The primitiveness of contemporary fatty acid biosynthesis was evaluated by using the thermodynamics and kinetics of its component reactions to estimate the extent of its dependence on powerful and selective catalysis by enzymes. Since this analysis indicated that the modern pathway is not primitive because it requires sophisticated enzymatic catalysis, we here propose an alternative pathway of primitive fatty acid synthesis that uses glycolaldehyde as a substrate. In contrast to the modern pathway, this primitive pathway is not dependent on an exogenous source of phosphoanhydride energy (ATP). Furthermore, the chemical spontaneity of its reactions suggests that it could have been readily catalyzed by the rudimentary biocatalysts available at an early stage in the origin of life.

Acetaldehyde↗
PubMed1991

Focal amyloidosis of the head and neck: evaluation with CT and MR imaging.

Localized amyloidosis of the head and neck was found retrospectively in the nasopharynx (n = 3) and orbit (n = 1) of four female patients (mean age, 32 years), three of whom had a prior history of antigenic stimulation. In all patients, computed tomography revealed a slightly high absorption and a relatively homogeneous, partially calcified mass. In the one patient who underwent magnetic resonance (MR) imaging, a distinctive loss of signal intensity was seen on the long repetition time/echo time sequence. This enhanced T2 relaxation may be due to (a) static or slowly fluctuating internal magnetic fields arising from adjacent amyloid protons held in relatively fixed positions within the beta-pleated sheet, resulting in quick phase dispersion; (b) chemical exchange and spin-spin interaction with adjacent water protons; and (c) diffusion through differences in diamagnetic susceptibility. This unusual appearance at MR imaging may improve the ability of radiologists to distinguish focal amyloidosis from many other diseases that affect the head and neck.

Adult↗
PubMed1990

Energy-rich glyceric acid oxygen esters: implications for the origin of glycolysis.

The apparent Gibbs free energy change of hydrolysis (delta G degrees', pH 7) of the 2- and 3-O-glyceroyl esters of 2- and 3-O-L-glyceroyl-L-glyceric acid methyl ester were measured at 25 degrees C. The 2- and 3-glyceroyl esters were found to be 'energy-rich' with delta G degrees' values of -9.1 kcal mol-1 and -7.8 kcal mol, respectively. This result indicates that the analogous 2- and 3-glyceroyl esters of polyglyceric acid are also 'energy-rich' and, therefore, could have acted as an energy source for primitive phosphoanhydride synthesis.

Energy Metabolism↗
PubMed1989

Model of early self-replication based on covalent complementarity for a copolymer of glycerate-3-phosphate and glycerol-3-phosphate.

Glyceraldehyde-3-phosphate acts as the substrate in a model of early self-replication of a phosphodiester copolymer of glycerate-3-phosphate and glycerol-3-phosphate. This model of self-replication is based on covalent complementarity in which information transfer is mediated by a single covalent bond, in contrast to multiple weak interactions that establish complementarity in nucleic acid replication. This replication model is connected to contemporary biochemistry through its use of glyceraldehyde-3-phosphate, a central metabolite of glycolysis and photosynthesis.

Evolution, Molecular↗
PubMed1989

Thermal synthesis and hydrolysis of polyglyceric acid.

Polyglyceric acid was synthesized by thermal condensation of glyceric acid at 80 degrees in the presence and absence of two mole percent of sulfuric acid catalyst. The acid catalyst accelerated the polymerization over 100-fold and made possible the synthesis of insoluble polymers of both L- and DL-glyceric acid by heating for less than 1 day. Racemization of L-glyceric acid yielded less than 1% D-glyceric acid in condensations carried out at 80 degrees C with catalyst for 1 day and without catalyst for 12 days. The condensation of L-glyceric acid yielded an insoluble polymer much more readily than condensation of DL-glyceric acid. Studies of the hydrolysis of poly-DL-glyceric acid revealed that it was considerably more stable under mild acidic conditions compared to neutral pH. The relationship of this study to the origin of life is discussed.

Evolution, Chemical↗
PubMed1988

Inflammatory diseases of the paranasal sinuses and mucoceles.

Inflammatory diseases of the paranasal sinuses are commonly encountered. In addition to the clinical evaluation, paranasal sinus films are often included for the diagnosis and follow-up. Complications of such infections and mucoceles are best evaluated by CT and MRI.

Cysts↗