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 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.

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.

The induction of transport channels by auxin

This work deals with measurements of the transport of radio-activity from [(3)H] indole acetic acid during early stages of auxin-induced vascular differentiation. Transverse wounds were made in stems of Phaseolus vulgaris L. and the radioactivity which was transported around these wounds was measured. Treatments with unlabelled auxin above the wounds increased transport within 16 hours of the time they were first applied while the maturation of vascular elements in response to these treatments started only on the 3rd day. It is concluded that increased transport is an early stage of vascular differentiation, and this phenomenon can account for the organized differentiation of vascular elements in vertical rows and defined bundles.

The three-dimensional structure of primary phloem systems

A method has been developed for staining the phloem so that its ramifications can be observed directly in thick preparations. This method is based on clearing the material with lactic acid, staining with lacmoid and observing it in sodium lactate. Phloem anastomoses between the primary vascular strands of stem internodes were found to be common in many plant species (18 out 26 studied). These anastomoses are possible channels for the lateral distribution of materials in the stem and for movement of assimilates upwards from the leaves.