Rate constants for the reaction of four different butyl radicals with molecular oxygen have been measured at room temperature. The radicals were generated by flash photolysis and their time decay was followed with a photoionization mass spectrometer. The radical concentrations were kept low to avoid complications from radical–radical reactions. Radical lifetimes were long, up to 50 msec, thus assuring that thermalized radicals were being studied. The rate constants, in units of 10−11 cm3 molecule−1 sec−1, are: n-butyl (0.75±0.14); s-butyl (1.66±0.22); t-butyl (2.34±0.39); 3-hydroxy s-butyl (2.8±1.8). No pressure dependence of the rate constants was observed over the range 1 to 4 Torr. In the absence of O2, the butyl radicals decay mainly by loss on the quartz surface of the reaction cell, with sticking coefficients in the range of 10−2 to 10−3. The Adiabatic Channel Model can predict the approximate absolute values of these rate constants using reasonable molecular parameters, but it fails to reproduce the observed trend of rate constants with radical ionization potential.
Discordant lymphomas are those in which two different histologic subtypes of non-Hodgkin's lymphoma are present simultaneously in the same patient at two or more separate disease sites. Discordance usually involves a lower grade follicular lymphoma in one anatomic site and a higher grade diffuse lesion elsewhere. A common type of discordance is seen in patients with a primary diagnosis of diffuse large-cell lymphoma (DLCL) who demonstrate bone marrow involvement by a lower grade lesion, such as a small cleaved cell or mixed small cleaved and large cell lymphoma. This study was undertaken to assess retrospectively the clinical implications of such bone marrow involvement, as well as the possible biologic mechanisms. Of the 59 DLCL cases studied, 20 (33.9%) showed evidence of bone marrow involvement, 14 of which were discordant (70%). The most significant findings included the following: Overall treatment responses and survivals in discordant patients with predominantly small cleaved cells in the marrow were similar to those in patients with no marrow involvement (mean survivals, 47.7 and 49 months, respectively), and were significantly longer than in patients with concordant marrow involvement (mean survival, 13.1 months, P < .05). Patients with discordant marrow infiltrates composed of a mixed cell population tended to do as poorly as those with concordant involvement. No clear-cut pattern of relapse in discordant patients was found, but persistence of small cleaved cells in some was reminiscent of lower grade B-cell lesions. Other features associated with lower grade lesions included older age, less incidence of central nervous system involvement, and lesser extent and proportion of marrow infiltration. Finally, in approximately half the cases with discordant involvement, lymphoma was present unilaterally, emphasizing the need to perform bilateral biopsies for staging.
Dr Rigamonti and colleagues seem to imply that MRI can reliably distinguish between a cavernous malformation and an arteriovenous malformation. Our own experience suggests that it may be difficult to discriminate between the two on radiographic grounds alone [l]. Indeed, the patient in question had a pathologically verified arteriovenous malformation. Nonetheless, the figure legend describing the MRI scan of Patient 1 should have stated, ". . . the MRI characteristics were thought to be typical of a vascular malformation," rather than an "arteriwenous malformation." We appreciate that Dr Rigamonti and colleagues brought this to our attention.
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