Ruptured abdominal aortic aneurysm.

Ruptured abdominal aortic aneurysm (AAA) continues to be one of the most lethal vascular pathologies we encounter. Its management demands prompt and efficient evaluation and repair. Open repair has traditionally been the mainstay of treatment. However, the introduction of endovascular techniques has altered the treatment algorithm for ruptured AAA in most major medical centers. We present recent literature and techniques for ruptured AAA and its surgical management.

Plant morphogenesis: long-distance coordination and local patterning.

The overall morphology of a plant is largely determined by developmental decisions taken within or near the terminally positioned apical meristems of shoots and roots. The spatial separation of these developmental centers emphasizes the need for long-distance signaling. The same signaling events may simultaneously coordinate differentiation within meristems and in the connecting vascular tissues. Recent genetic and molecular analyses not only confirm the proposed role of auxin as a coordinating signal across the plant, but also implicate auxin as a patterning signal in embryo and meristem organization.

Integrating cellular and organismic aspects of vascular differentiation.

Vascular differentiation can be studied at two levels, and they should complement one another: as an aspect of integrated plant development and as cellular processes. The differentiation of organized strands that connect between organs is induced by polar auxin flow, towards the roots. Anatomy, therefore, can be a complementary method of observing polarity and its changes. As expected for a self-correcting and essential system, vascular patterning mutations are relatively rare and have pleiotropic effects, including modifications of responses to auxin and its transport. Tissue polarity both expresses and depends on auxin transport, a feedback that could account for the determined nature of polarity as well as the gradual canalization of differentiation to vascular strands. This predicts that the molecules responsible for polarity will be localized gradually as differentiation proceeds. Further, a modified location of these molecules can be expected to precede anatomical expressions of a new, regenerated, polarity. Tracheary differentiation is probably the best studied example of cell differentiation. Within the plant, however, this differentiation is coupled to oriented cell growth either along or at right angles to the axis of auxin flow, depending on tissue competence. Differentiation is also coupled to the differentiation of the other components of the vascular system. There are, presumably, early joint stages to these differentiation processes, but what they are remains an intriguing problem.

The real-time interactive 3-D-DVA for robust coronary MRA.

A graphical user interface (GUI) has been developed which enables interactive feedback and control to the real-time diminishing variance algorithm (DVA). This interactivity allows the user to set scan parameters, view scan statistics, and view image updates during the course of the scan. In addition, the DVA has been extended to simultaneously reduce motion artifacts in three dimensions using three orthogonal navigators. Preliminary in vivo studies indicate that these improvements to the standard DVA allow for significantly improved consistency and robustness in eliminating respiratory motion artifacts from MR images, particularly when imaging the coronary arteries.

Prospective MR signal-based cardiac triggering.

A cardiac motion compensation method using magnetic resonance signal-based triggering is presented. The method interlaces a triggering pulse sequence with an imaging sequence. The triggering sequence is designed to measure aortic blood velocity, from which cardiac phase can be inferred. The triggering sequence is executed repeatedly and the acquired data processed after each sequence iteration. When the desired phase of the cardiac cycle is detected, data are acquired using the imaging sequence. A signal-processing unit of a conventional scanner is used to process the triggering data in real time and issue triggering commands. Alternatively, a workstation, with a bus adaptor, can access data as they are acquired, process and display the data, and issue triggering commands. With a graphical user interface, the triggering pulse sequence and data-processing techniques can be modified instantaneously to optimize triggering. The technique is demonstrated with coronary artery imaging using both conventional two-dimensional Fourier transform scans and spiral trajectories.

Fast magnetic resonance coronary angiography with a three-dimensional stack of spirals trajectory.

In this work, three-dimensional (3D) spiral imaging has been utilized for magnetic resonance coronary angiography. Spiral-based 3D techniques can dramatically reduce imaging time requirements compared with 3D Fourier Transform imaging. The method developed here utilized a "stack of spirals" trajectory, to traverse 3D k-space rapidly. Both thick-slab volumes encompassing the entire coronary tree with isotropic resolution and thin-slab volumes targeted to a particular vessel of interest were acquired. Respiratory compensation was achieved using the diminishing variance algorithm. T2-prepared contrast was also applied in some cases to improve contrast between vessel and myocardium, while off-resonance blurring was minimized by applying a linear correction to the acquired data. Images from healthy volunteers were displayed using a curved reformatting technique to view long segments of vessel in a single projection. The results demonstrate that this 3D spiral technique is capable of producing high-quality coronary magnetic resonance angiograms.

The diminishing variance algorithm for real-time reduction of motion artifacts in MRI.

A technique has been developed whereby motion can be detected in real time during the acquisition of data. This enables the implementation of several algorithms to reduce or eliminate motion effects from an image as it is being acquired. One such algorithm previously described is the acceptance/rejection method. This paper deals with another real-time algorithm called the diminishing variance algorithm (DVA). With this method, a complete set of preliminary data is acquired along with information about the relative motion position of each frame of data. After all the preliminary data are acquired, the position information is used to determine which data frames are most corrupted by motion. Frames of data are then reacquired, starting with the most corrupted one. The position information is continually updated in an iterative process; therefore, each subsequent reacquisition is always done on the worst frame of data. The algorithm has been implemented on several different types of sequences. Preliminary in vivo studies indicate that motion artifacts are dramatically reduced.

Real-time motion detection in spiral MRI using navigators.

A technique has been developed whereby motion can be detected in real time during the acquisition of data. This enables the implementation of an algorithm to accept or reject and reacquire data during a scan. Frames of data with motion are rejected and reacquired on the fly so that by the end of the scan, a complete motion-free data set has been acquired. The algorithm has been implemented on several different types of sequences. Preliminary in vivo studies indicate that motion artifacts are dramatically reduced.

The development and patterning of stomata and glands in the epidermis of Peperomia.

The leaf epidermis of Peperomia obtusifolia includes both stomata and glands, distributed in a joint spacing pattern. The questions asked concerned the relations between the development of glands and stomata and the determination of their distributions within the epidermis. For these purposes it was essential to follow development in vivo, by repeated replicas of the same epidermal surface. The development of both stomata and glands started by characteristic divisions. These were generally unequal and it was the smaller product that became the mother cell of the future specialized structure. The initial divisions differed, so that the nature of the mature structure, as a stoma or a gland, could normally be predicted at an early stage. But glands and stomata still shared developmental processes: their formation involved additional characteristic divisions in the mother cell and oriented divisions in neighbouring cells. Furthermore, some lineages started as glands and matured as stomata and vice versa. Statistical measurements showed that each individual structure was surrounded by a region that was free of both similar and other specialized structures. Where these regions involved stomata they could be accounted for by the cell lineages forming not only a stoma or a gland but also their surrounding cells. Yet the relations between neighbouring glands had an additional component, indicating a specific inhibition that declined gradually as the distance from the gland increased.

Squamous carcinoma of the mid-esophagus. A survival study.

A survival study for squamous carcinomas of the mid-esophagus treated by Southern California Permanente Medical Group in the interval of 1954 to 1988 was undertaken. Radiation therapy and surgery were equally efficacious in terms of 5-year survival for patients without distant disease and performance status sufficient to tolerate treatment (11% and 16%, respectively). There was no survival benefit for patients treated with palliative surgery. Less invasive endoscopic means along with chemotherapy and radiation for palliation are recommended except for special circumstances. Optimal treatment combinations remain to be discovered.

Development of immature stomata: evidence for epigenetic selection of a spacing pattern.

In Sansevieria trifasciata as many as half the potential stomata remain immature. The development of all stomatal structures started at the same time and the early stages of the development of immature stomata had no special characteristics. Statistical analysis showed that the mature stomata were more evenly spaced than all potential stomata, both mature and immature. Furthermore, the distribution of mature stomata per unit area was more predictable or orderly than comparable structures of a random model that developed in the same way. These facts indicate that a nonrandom loss of many stomata by "immaturity" is a major determinant, acting during rather than preceding development, of the distribution of the mature, functional stomata. Thus in Sansevieria there is a selection of an epidermal pattern from an excess of cells that undergo the early stages of stomatal development.

An effective self-retaining retractor for anorectal procedures.

A self-retaining retractor technique is described for anorectal surgery eliminating many of the problems inherent in the commonly used instruments. It is particularly useful in endorectal pull-through procedures in which the exact level of anastomosis within the anorectal canal is of great importance.

Adenocarcinoma arising in Barrett's esophagus.

A review of nine adenocarcinomas of the esophagus arising in Barrett's epithelium was undertaken. We found the disease among white males disproportionately. Risk factors and incidence rate remain to be clarified. Only one patient was in a surveillance program and only he had carcinoma discovered "early." He still survives while only one of the eight whose diagnosis followed investigation of symptoms remains alive.

Use of MRI in evaluation of anorectal anomalies.

Congenital anorectal anomalies present with a wide spectrum of anatomical deformity. The level of atresia, the extent of the development of the pelvic musculature, and the presence of associated anomalies all greatly influence treatment options. Further complexity may be introduced by previous attempts at correction. Magnetic resonance imaging (MRI) recently has been suggested as an effective tool in evaluation of such patients for surgical repair. Thirteen patients undergoing evaluation for either primary or secondary operations for imperforate anus were studied with MRI. Age range was newborn to 26 years. These patients had anorectal deformities in various stages of treatment--from newly diagnosed imperforate anus in the newborn to patients who had undergone previous surgical repair of their deformity with poor results. In newborns, MRI was very useful in assessing the level of atresia and determining whether perineal repair was advisable. In older patients with high atresias, MRI was useful in planning operative strategy and predicting the outcome by providing information about the pelvic musculature. This information was directly related to the size of the patient, ie, the larger, and therefore the older the patient, the more detail MRI provided about the pelvic musculature. Especially in secondary cases, this information proved to be helpful in determining the cause of the initial failure, ie, lack of adequate pelvic musculature or poor placement of the distal colon in relation to the striated muscle complex at the initial operation. MRI demonstrated previous unsuspected lesions such as tethered cord, sacral deformity or urinary tract abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

Epigenetic selection: an alternative mechanism of pattern formation.

It is commonly assumed that patterned development is specified by pre-patterns or programs, actual development being a necessary consequence of previous conditions. However, the variability of normal development and its regenerative capacities are evidence for additional patterning processes. Predictable mature structures could result from continued "epigenetic selection" of the most appropriate developmental events. This selection would occur from an excess of possibilities that are genetically equivalent. The final balanced state would be specified by the genes, and the developmental system could gravitate towards this state without a detailed program. Selection could result from competition between cells and tissues for limiting developmental signals. The success or continuation of events that could start randomly would depend on feedback relationships with complementary developmental events. Specialized processes could be gradually localized if differentiation itself consumed limiting signals and if this consumption increased as differentiation proceeded. Spatial patterns could be formed if the movement of signals was gradually facilitated along the axes where it were initiated by diffusion. For example, induced facilitated transport could be the basis of an advantage of multicellular centers over scattered cells that have specialized in the same way. If epigenetic selection has a developmental role it requires a revision of common views concerning the cellular traits and the gene functions necessary for patterned development. An example of these traits is that cells should be expected to respond to changes in signal availability, not necessarily to signal concentration at any given time.

Cellular interactions in tissue and organ development.

Developmental patterns result from combinations of interactions and intracellular programmes. The purpose here is to define the roles of interactions wherever possible and to consider their major parameters, such as the timing of their action, their specificity and the distances over which they occur. The approach is one of a board survey, attempting to outline major interaction systems on the basis of information from different sources. The evidence concerning interactions that control development must come primarily from development itself. Both disturbed, as during regeneration and grafts, and normal development are relevant. Growing apices interact over relatively long distances. They reduce the development of similar apices and induce the development of axial tissues that connect them to the plant. Young shoot tissues also induce the development of root apices and vice versa. These various effects can be understood on the basis of a hormonal feedback involving auxins and cytokinins. Vascular differentiation, furthermore, is a cellular expression of these interactions. It occurs along the flow of auxin from the young tissues of the shoot towards the root apices. This flow is canalized by a positive feedback between cell polarization and the polar flow that both controls and results from this polarization. Structural relations between pholem and xylem, limitations of regeneration and the formation of rays all indicate the existence of additional, radial interactions. The fate of individual cells in development is varied and often follows no recognizable rules. This indicates interactions that operate on the size of a tissue or organ rather than on its precise cellular development. On the other hand, the continuity of plasmodesmata, wall thickenings and cytoplasmic strands demonstrate local interactions between neighbouring cells. It is concluded that, though the possibilities of developmental interactions may be bewildering, the list, when known, may not be all that long. The interactions specify orientation and quantity rather than the precise fate of cells. Their effects are gradual and they involve feedback loops. Growth factors, even known growth factors, play surprisingly large roles in cellular interactions. Such controls whose effect is gradual and general could provide a basis for developmental plasticity.