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Biomedical subjects

A L Williams

Publications and source records attributed to A L Williams.

At least 91 records · Page 5Linked to original sources
PubMed1983

Regulation of acetohydroxy acid synthase activities in adenyl cyclase-deficient strains of Escherichia coli K-12.

Previous findings suggested that cyclic AMP was involved in the regulation of ilvB(AHASI) only and that ilvG (AHASII) and ilvHI (AHASIII) were not controlled by this nucleotide. In this study, derepression patterns of total AHAS activities (ilvB and ilvHI) in adenyl cyclase-negative strains (i.e. cya-) were substantially reduced as contrasted with AHAS activity observed for cya+ strains. Further, the parental strains (cya+) consistently exhibited higher levels of AHAS activity than mutant strains (cya-) during carbon and energy downshifts. Other data suggested that the valine derepression signal could not override the necessity for cya gene product to yield maximal derepression of AHAS gene activities. Cyclic AMP stimulated AHAS gene activities under both in vivo and in vitro assay conditions. Thus, these data provide evidence for an absolute requirement of cAMP for maximal expression of the genes encoding for AHAS activities of E. coli K-12.

Acetolactate Synthase↗
PubMed1983

Computed tomographic study of hormone-secreting microadenomas.

A review was made of the computed tomographic (CT) studies of 33 patients with hormone-secreting microadenomas that had been verified by transsphenoidal surgery and endocrinologic evaluation. In previous studies in small series of patients, the CT appearance of pituitary microadenomas has been reported as hypodense, isodense, and hyperdense. In this study, CT showed a region of diminished enhancement and usually an enlarged pituitary gland in cases of prolactin-secreting adenomas. HGH- or ACTH-secreting adenomas were less consistently hypodense. It is concluded that hypodensity and enlargement in the pituitary gland are the most useful criteria for identification of microadenomas. Some technical factors that may affect the CT appearance of microadenomas and lead to conflicting reports are discussed.

Adenoma↗
PubMed1983

Computed tomography of the articulations and ligaments at the occipito-atlantoaxial region.

The computed tomographic (CT) appearance of the occipito-atlantoaxial articulations and ligaments was analyzed using the CT/T 8800 and 9800 scanners with and without intravenous or intrathecal contrast media. Osseous and ligamentous structures in dissected or sectioned anatomic specimens were correlated with structures seen on the CT images, and the articulations and transverse, alar, and apical ligaments were identified. It is concluded that such an analysis, which has not been done in detail previously, should facilitate the diagnosis of cervical soft-tissue injuries and abnormalities.

Atlanto-Axial Joint↗
PubMed1983

Differential CT diagnosis of extruded nucleus pulposus.

The detection and differential diagnosis of extruded (free) disk fragments by CT has not been described in detail. We reviewed the lumbar CT scans of 57 patients with extruded disk fragments and of 31 patients in whom the CT appearance of disk fragments was simulated by other processes. An extruded disk fragment commonly appears on CT scans as an epidural mass that must be distinguished from either an epidural tumor or an anomalous root sheath. A normal posterior disk margin does not exclude a disk herniation when the nuclear fragment is extruded. Free disk fragments can be differentiated from root-sheath anomalies and tumors in most cases by measuring tissue densities and analyzing adjacent bone.

Contrast Media↗
PubMed1983

Pterygopalatine fossa: computed tomographic studies.

The CT appearance of the pterygopalatine fossa is described in detail. Anatomic and CT sections were compared in cadavers and patients in axial and coronal CT planes to identify the osseous configuration and vascular and neural contents of the fossa. The normal fat, soft-tissue, and osseous margins are altered by neoplasms in the fossa. CT is an effective technique to evaluate the fossa and contiguous area.

Cadaver↗
PubMed1983

CT diagnosis of degenerative disc disease. The bulging annulus.

Computed tomography can accurately distinguish a bulging disc with intact annulus from a herniated nucleus pulposus in most patients. A bulging annulus should be diagnosed when CT scans demonstrate generalized extention of the disc margins beyond the adjacent vertebral body margins. A herniated nucleus may be diagnosed by a CT scan when there is focal protrusion of the disc margin beyond the vertebral body margins. However, correlation between clinical and CT findings remains a critical factor in determining the significance of an abnormality detected by a CT scan.

Humans↗
PubMed1982

Computed tomographic appearance of the bulging annulus.

Criteria have not been established for differentiating herniated nucleus pulposus and bulging annulus fibrosus by computed tomography (CT). The CT diagnosis of a bulging annulus was evaluated by correlating the CT and anatomic appearance of cadaver lumbar spines, and by comparing CT and surgical findings in patients undergoing lumbar laminectomy. We found that in anatomically or surgically verified bulging annulus, CT showed generalized extension of the disk margin beyond the vertebral body margins. Therefore, bulging annulus can be distinguished by CT from herniated nucleus, which has a focal, usually posterolateral, protrusion of the disk margin.

Adolescent↗
PubMed1982

Computed tomography of the medulla.

The medulla was studied in cadavers and in 100 patients both with and without the intrathecal administration of contrast material. The computed tomographic (CT) anatomy was correlated with the appearance of anatomic dissections. The pyramids, olives, and inferior cerebellar peduncles produced characteristic contours on cross sections of the medulla. The hypoglossal nerve by its location and course in the medullary cistern could be distinguished from the glossopharyngeal, vagal, and spinal accessory nerves. For optimal evaluation of the medulla, intrathecal administration of metrizamide and 5- and/or 1.5-mm-thick axial and coronal sections are recommended.

Accessory Nerve↗
PubMed1982

Spondylolysis studied with computed tomography.

Spinal CT scans, plain radiographs, and medical records of 81 patients with an abnormal pars interarticularis were reviewed to define the CT criteria for spondylolysis. In many cases, it was difficult to detect because it simulated the adjacent facet joints; however, it could be differentiated by careful analysis of the section level and the contiguous facet joints, which usually had regular cortical surfaces (in contrast to the pars defects). Spondylolysis was evident on the lateral localizer image in most cases. In some patients the pars appeared abnormally narrow and elongated or sclerotic as well as interrupted. In a few cases, CT demonstrated a pars defect which was not effectively shown by the plain radiographs. In one patient, a herniated disk was also seen.

Adult↗
PubMed1982

CT recognition of lateral lumbar disk herniation.

Although computed tomography (CT) has been shown to be useful in diagnosing posterolateral and central lumbar disk herniations, its effectiveness in demonstrating lateral herniated disks has not been emphasized. The myelographic recognition of those herniations may be difficult because root sheaths or dural sacs may not be deformed. A total of 274 CT scans interpreted as showing lumbar disk herniation was reviewed. Fourteen (5%) showed a lateral disk herniation. The CT features of a lateral herniated disk included: (1) focal protrusion of the disk margin within or lateral to the intervertebral foramen; (2) displacement of epidural fat within the intervertebral foramen; (3) absence of dural sac deformity; and (4) soft-tissue mass within or lateral to the intervertebral foramen. Because it can image the disk margin and free disk fragments irrespective of dural sac or root sheath deformity, CT may be more effective than myelography for demonstrating the presence and extent of lateral disk herniation.

Adult↗
PubMed1981

Differential diagnosis of intrasellar tumors by computed tomography.

The specificity of the computed tomography (CT) diagnosis of intrasellar adenoma has not been studied. We compared the CT findings in intrasellar meningiomas, craniopharyngiomas, aneurysms, and metastases with those of pituitary adenomas. Calcification was a features of intrasellar meningiomas, aneurysms, and craniopharyngioma,s but not a typical feature of adenomas. Low-density regions representing necrosis or cyst were found in most types of intrasellar tumors. Eccentricity, hyperostosis, and bone destruction were useful signs of aneurysm, meningioma, and metastasis, respectively. Since adenoma cannot always be distinguished from another intrasellar mass, angiography to demonstrate tumor angioarchitecture may be needed to characterize some neoplasms or to confirm an intrasellar aneurysm.

Adenoma↗
PubMed1981

Recognizing the empty sella by CT: the infundibulum sign.

Inaccuracy in recognizing the empty sella by conventional computed tomography (CT) techniques derives from diverse intrasellar cystic structures that are not distinguished from it. In 23 cases of presumed empty sella, it was observed that the pituitary stalk within the enlarged sella (infundibulum) was demonstrated by thin (1.5 mm) coronal CT sections. ALthough the diagnosis was not proven by conventional studies, the normal appearance of the infundibulum is believed to exclude an intrasellar cyst or tumor as the cause of sellar enlargement. Coronal CT sections with thin slices and intravenous contrast enhancement are recommended when empty sella is to be documented by CT. When the infundibulum is not demonstrated by this technique, CT with intrathecal enhancement may be warranted.

Empty Sella Syndrome↗