Computer modeling of cerebral blood flow following internal carotid artery occlusion.

It is difficult to predict the adequacy of the collateral blood flow in patients who undergo internal carotid artery occlusion. In order to address this difficulty, the authors have created a computer model of the cerebral circulation. This model features individualized simulations of the Circle of Willis and its afferent and efferent branches which can predict changes in flow that will occur during internal carotid artery occlusion. Analysis of the flow predictions suggests that in patients with a symmetric Circle of Willis the anterior communicating artery is the major conduit of collateral blood supply. In patients with a small anterior communicating artery, the posterior communicating arteries become more important as sources of collateral flow, but they cannot supply as much flow as in the case of a normal anterior communicating artery. Sensitivity studies show that changes in the dimensions of each artery affect the flow throughout the system, such that the arteries in the cerebral circulation must be analyzed as a network rather than as isolated elements. This computer model of the cerebral circulation may help clinicians predict the adequacy of collateral blood supply in patients who undergo internal carotid artery occlusion.

Tetrahydrobiopterin synthesis and inducible nitric oxide production in pulmonary artery smooth muscle.

We recently reported (Am. J. Respir. Cell Mol. Biol. 7: 471-476, 1992) that a mixture of lipopolysaccharide (LPS) and cytokines produced a time-dependent increase in mRNA and protein expression of inducible nitric oxide synthase (iNOS) in cultured rat pulmonary artery smooth muscle cells (RPASM). In the current study we extend observations on regulation of iNOS in RPASM by showing that de novo synthesis of tetrahydrobiopterin (BH4) is critical for LPS and cytokine-induced NO production. A mixture of LPS and the cytokines gamma-interferon, interleukin-1 beta, and tumor necrosis factor-alpha increased steady-state levels of mRNA of GTP-cyclohydrolase-I (GTP-CH), the rate-limiting enzyme in BH4 biosynthesis. Levels of mRNA to GTP-CH became detectable by 4 h, with further increases at 24 h by Northern blot analysis and reverse-transcriptase polymerase chain reaction. Total intracellular biopterin levels, undetectable under basal conditions, increased after 24 h exposure to LPS and cytokines (to 32.3 +/- 0.8 pmol/mg protein). LPS and cytokine-induced NO production, determined by nitrite concentrations in the medium, was decreased in a concentration-dependent manner by the GTP-CH inhibitor, 2,4-diamino-6-hydroxypyrimidine (DAHP) at 24 h. DAHP also inhibited completely the LPS- and cytokine-induced accumulation of intracellular biopterins. Sepiapterin, which supplies BH4 through a salvage pathway independent of GTP-CH, reversed the effect of DAHP on LPS and cytokine-induced NO production.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial callosal resection for pericallosal aneurysms.

The surgical treatment of aneurysms that arise at the origin of the pericallosal artery is technically difficult. This report describes a technique that improves the exposure of the proximal vasculature during a craniotomy for pericallosal aneurysms. A portion of the corpus callosum was resected in two patients before the manipulation of their aneurysms. The resection provided excellent exposure of the A2 segment of the anterior cerebral artery, and both aneurysms were clipped safely. Neither patient exhibited signs of hemispheric disconnection. The authors conclude that partial callosal resection improves access to the proximal vessels during procedures for pericallosal aneurysms.

Spontaneous spinal epidural hematoma.

Two cases of the spontaneous occurrence of spinal epidural hematomas of the high thoracic area are reported. Both acute and subacute presentations of paraplegia are represented. Neither patient had experienced any significant antecedent trauma. No predisposing medical conditions were present. Both patients recovered to independent ambulation following timely operative intervention. The pertinent literature on spinal epidural hematomas is reviewed, and the differential diagnosis of this entity is discussed. The need for prompt diagnosis and surgical treatment to achieve the best neurological outcome is emphasized.

Meningioma associated with aneurysm and subarachnoid hemorrhage: case report and review of the literature.

A patient presented with spontaneous subarachnoid hemorrhage after a prolonged episode of coughing. A preoperative computed tomographic (CT) scan confirmed subarachnoid hemorrhage, but demonstrated no other lesion. Arteriography revealed an ophthalmic artery aneurysm. Operation revealed the aneurysm to be intracavernous without sign of prior rupture; however, a small hemorrhagic meningioma was removed from the ipsilateral anterior clinoid process. In this case, coincidental meningioma and aneurysm presented as a subarachnoid hemorrhage secondary to tumor hemorrhage. The follow-up of cases of subarachnoid hemorrhage with negative arteriography with sequential CT scans is discussed.