Biomedical subjects
Publications and source records attributed to A Horowitz.
Accessory salivary gland tissue is well recognized and is found in 21 per cent of the population. Tumours of the accessory salivary tissue are rare and comprise only 1 per cent of all parotid gland tumours. A pleomorphic adenoma of Stensen's duct is described. A circular constriction of this duct by the tumour with retention of saliva in the parotid gland was observed.
A two-dimensional incompressible plane-stress finite element is formulated for the simulation of the passive-state mechanics of thin myocardial strips. The formulation employs a total Lagrangian and materially nonlinear approach, being based on a recently proposed structural material law, which is derived from the histological composition of the tissue. The ensuing finite element allows to demonstrate the mechanical properties of a single myocardial layer containing uniformly directed fibers by simulating various loading cases such as tension, compression and shear. The results of these cases show that the fiber direction is considerably stiffer than the cross-fiber direction, that there is significant coupling between these two directions, and that the shear stiffness of the tissue is lower than its tensile and compressive stiffness.
A three dimensional incompressible and geometrically as well as materially nonlinear finite element is formulated for future implementation in models of cardiac mechanics. The stress-strain relations in the finite element are derived from a recently proposed constitutive law which is based on the histological composition of the myocardium. The finite element is formulated for large deformations and considers incompressibility by introducing the hydrostatic pressure as an additional variable. The results of passive loading cases simulated by this element allow to analyze the mechanical properties of ventricular wall segments, the main of which are that the circumferential direction is stiffer than the longitudinal one, that its shear stiffness is considerably lower than its tensile and compressive stiffness and that, due to its mechanically prominent role, the collagenous matrix may affect the myocardial perfusion.
A three-dimensional constitutive law is proposed for the myocardium. Its formulation is based on a structural approach in which the total strain energy of the tissue is the sum of the strain energies of its constituents: the muscle fibers, the collagen fibers and the fluid matrix which embeds them. The ensuing material law expresses the specific structural and mechanical properties of the tissue, namely, the spatial orientation of the comprising fibers, their waviness in the unstressed state and their stress-strain behavior when stretched. Having assumed specific functional forms for the distribution of the fibers spatial orientation and waviness, the results of biaxial mechanical tests serve for the estimation of the material constants appearing in the constitutive equations. A very good fit is obtained between the measured and the calculated stresses, indicating the suitability of the proposed model for describing the mechanical behavior of the passive myocardium. Moreover, the results provide general conclusions concerning the structural basis for the tissue overall mechanical properties, the main of which is that the collagen matrix, though comprising a relatively small fraction of the whole tissue volume, is the dominant component accounting for its stiffness.
A 37-year-old patient with acute nonlymphatic leukemia developed gastrointestinal phycomycosis during failure in bone marrow production. The clinical presentation was of acute typhlitis. Laparotomy revealed a necrotic mass in the region of the iliocecal valve, and on histologic examination hyphae of phycomycetes with invasion of the blood vessels were seen. The patient died as a result of widespread infection.
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Three healthy teenagers were exposed to a single pelvic x-ray irradiation as part of sterilization experiments performed in the Auschwitz concentration camp in 1943. Single and multiple carcinomas of the colon and rectum developed 40 years later in the radiation field. Histologic examination of surgical specimens revealed severe radiation-induced changes in all layers of tumor-adjacent areas. In contrast to previous reports of radiation-induced large bowel cancers, these women had not undergone repeated courses of radiation, had no known co-existing disease that might raise the risk for colonic and rectal malignancies, and had an extremely long and remarkably similar latency period. These cases emphasize the need for long-term surveillance in previously radiated patients. Since thousands of teenagers were subjected to similar sterilization experiments, awareness of this association might help in the early diagnosis of additional cases.
A 53-year-old patient with no past history of rheumatic fever or lues presented with severe aortic regurgitation, underwent hemodynamic evaluation, and subsequently, an uneventful aortic valve replacement. The initial pathological interpretation was nonspecific aortitis. Six months following surgery arthralgia, muscular pain, difficulty in mastication, and fatigue occurred. There was no fever, however, sedimentation rate was 100/130. Cardiac examination was normal. Review of the pathological specimens revealed granulomatous arteritis with giant cells, typical of giant cell arteritis. Though the association of aortic regurgitation and giant cell arteritis is well recognized, only two such cases of severe aortic regurgitation requiring valve replacements have yet been described, of them, one probably had Takayasu's arteritis. An accurate diagnosis is of importance since steroid treatment is effective, and if introduced early, the inflammatory process may be arrested.
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Differences in the energetics of breast carcinomas and benign breast tumors were monitored by recording their high-energy phosphate concentrations using phosphorus-31 magnetic resonance (MR) spectroscopy. Analysis of the P-31 spectra of biopsy samples from five benign breast tumors and nine breast carcinomas showed that the concentrations of nucleoside triphosphates and phosphomonoesters are consistently higher in the carcinomas than in the benign tumors by an average factor of about three. In addition, the chemical shift differences between the alpha-adenosine triphosphate (alpha-ATP) and beta-ATP signals and between the gamma-ATP and beta-ATP signals were larger by about 0.2 ppm in the carcinomas. These differences result from the lower fraction of magnesium-bound ATP found in the carcinomas under our experimental conditions and reflect a decrease of about two in the concentration of free magnesium ions in the carcinomas relative to that in the benign tumors. Despite the limited number of tumors studied, the results suggest that in vivo P-31 MR spectroscopy may become a reliable method for the diagnosis of breast tumors.
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Primary chondrosarcoma of the extraskeletal soft tissue is rare, usually occurring in the upper and lower extremities. We report the first case of this neoplasm arising in the kidney.
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Recent studies indicate that although cellular DNA is the critical target in the action of initiating carcinogens, specific membrane-associated receptors mediate the actions of certain tumor promoters. A stereochemical model is presented to explain how three different types of tumor promoters (phorbol esters, indole alkaloids, and polyacetates) can interact with the same class of cellular receptors. Multistage chemical carcinogenesis might involve progressive alterations in the expression of cellular DNA sequences homologous to oncogenes and regulatory sequences in certain retroviruses. We found that the oncogene c-mos is not rearranged or expressed in a series of carcinogen-transformed murine C3H 10T112 cells. These cells do express, however, a unique set of poly(A)+ RNAs that contain sequences homologous to the Moloney leukemia virus long terminal repeat sequence. Studies are in progress to determine the significance of this finding with respect to the carcinogenic process.
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N6-Methyladenosine (m6A) residues, which are found internally in viral and cellular mRNA populations at the sequences Apm6ApC and Gpm6ApC, have been proposed to play a role in mRNA processing and transport. We have developed a sensitive approach to analyze the level and location of m6A in specific purified cellular mRNAs in an attempt to correlate m6A location with function. Polyadenylylated mRNA is hybridized to cDNA clones representing the full size mRNA under study or fragments of it, and the protected RNA is digested and labeled with polynucleotide kinase in vitro. After enrichment for m6A with anti-m6A antibody, the [32P]-pm6A is separated on TLC plates, and compared with the total amount of radiolabeled nucleotides. Using this combination of in vitro RNA labeling and antibody selection, we were able to detect m6A in purified stable mRNAs that cannot be readily labeled in cells with greater sensitivity than was possible by previous techniques. We applied this technique to bovine prolactin mRNA and showed that this mRNA contains m6A. Moreover, all of the m6A residues in this message are found within the 3' two-thirds of the molecule and are highly concentrated (61%) within a sequence of 108 nucleotides at the 3' noncoding region of the message. The nonrandom distribution of m6A in a specific cellular mRNA, as demonstrated for bovine prolactin, will have to be taken into account when designing a model for m6A function.