Agenesis of the posterior arch of the atlas

PURPOSE: To illustrate the radiological findings and review the current literature concerning a rare congenital abnormality of the posterior arch of the atlas. CASE REPORT: An adult female without neurological symptoms presented with an absent posterior arch of the atlas, examined with plain films and helical computerized tomography. Complete agenesis of the posterior arch of the atlas is a rare entity that can be easily identified by means of plain films. Although it is generally asymptomatic, atlantoaxial instability and neurological deficits may occur because of structural instability. Computerized tomography provides a means of assessing the extent of this abnormality and can help evaluate the integrity of neural structures. Although considered to be rare entities, defects of the posterior arch of the atlas may be discovered as incidental asymptomatic findings in routine cervical radiographs. Familiarity with this abnormality may aid medical professionals in the correct management of these cases.

Total agenesis of the left pericardium

This is the report of a 46-year-old patient with the preoperative diagnosis of an atrial septal defect (ASD) of the ostium secudum type. After sternectomy, partial agenesis of the left pericardium was diagnosed. It is our opinion that, if the radiographic picture is suggestive of this entity, a clinical search for cardiopulmonary anomalies should be performed, because the majority of these associated anomalies can and should be surgically corrected.

Agenesis or pseudoagenesis of the dorsal pancreas

The authors present an evidence-based case report of a patient with agenesis or pseudoagenesis of the dorsal pancreas.

Axonal pathfinding mechanisms at the cortical midline and in the development of the corpus callosum

The corpus callosum is a large fiber tract that connects neurons in the right and left cerebral hemispheres. Agenesis of the corpus callosum (ACC) is associated with a large number of human syndromes but little is known about why ACC occurs. In most cases of ACC, callosal axons are able to grow toward the midline but are unable to cross it, continuing to grow into large swirls of axons known as Probst bundles. This phenotype suggests that in some cases ACC may be due to defects in axonal guidance at the midline. General guidance mechanisms that influence the development of axons include chemoattraction and chemorepulsion, presented by either membrane-bound or diffusible molecules. These molecules are not only expressed by the final target but by intermediate targets along the pathway, and by pioneering axons that act as guides for later arriving axons. Midline glial populations are important intermediate targets for commissural axons in the spinal cord and brain, including the corpus callosum. The role of midline glial populations and pioneering axons in the formation of the corpus callosum are discussed. Finally the differential guidance of the ipsilaterally projecting perforating pathway and the contralaterally projecting corpus callosum is addressed. Development of the corpus callosum involves the coordination of a number of different guidance mechanisms and the probable involvement of a large number of molecules.

Heterotaxy syndrome: a case report

Heterotaxy syndrome is defined as an abnormal arrangement of some organs and vessels in association with dysmorphism. The authors describe the case of a patient with heterotaxy syndrome with poliesplenia incidentally diagnosed during imaging evaluation (computed tomography and small bowel barium study) of unrelated pathological condition.

Anomalia da via biliar extra-hepática

We show an anatomical modification of extrahepatic biliary ducts in a fifty-eight years old female who presented right hipocondric pain, jaundice and fever two months after cholecystectomy. The patient underwent ERCP wich showed an anatomical modification that consists in an union of the right and left hepatic ducts, with insertion into the cystic duct, right hepatic duct, being a choledochus agenesis.

Herlyn-Werner-Wunderlich syndrome: a case report

Herlyn-Werner-Wunderlich (HWW) syndrome is a rare congenital disorder of the Müllerian ducts in which there is uterus didelphys, obstructed hemivagina and unilateral renal agenesis. The most common presentation is an abdominal mass secondary to hematocolpos, pain and dysmenorrhea. However, in some cases, such as the one we present here, menses are normal due to an obstructed hemivagina, and diagnosis can be delayed. We describe evaluation and surgical management of a 13-year-old girl with this condition who was diagnosed by computed tomography (CT) scan and confirmed by pelvic ultrasound and surgical exploration, as well as a review of the literature.

Interhemispheric connections between primary visual areas: beyond the midline rule

In the last five years, a number of detailed anatomical, electrophysiological, optical imaging and simulation studies performed in a variety of non-human species have revealed that the functional organization of callosal connections between primary visual areas is more elaborate than previously thought. Callosal cell bodies and terminals are clustered in columns whose correspondence to features mapped in the visual cortex, such as orientation and ocularity, are starting to be understood. Callosal connections are not restricted to the vertical midline representation nor do they establish merely point-to-point retinotopic correspondences across the hemispheres, as traditionally believed. In addition, anatomical studies have revealed the existence of an ipsilateral component of callosal axons. The aim of this short review is to propose how these new data can be integrated into an updated scheme of the circuits responsible for assembling the primary visual field map.

One hundred million years of interhemispheric communication: the history of the corpus callosum

Analysis of regional corpus callosum fiber composition reveals that callosal regions connecting primary and secondary sensory areas tend to have higher proportions of coarse-diameter, highly myelinated fibers than callosal regions connecting so-called higher-order areas. This suggests that in primary/secondary sensory areas there are strong timing constraints for interhemispheric communication, which may be related to the process of midline fusion of the two sensory hemifields across the hemispheres. We postulate that the evolutionary origin of the corpus callosum in placental mammals is related to the mechanism of midline fusion in the sensory cortices, which only in mammals receive a topographically organized representation of the sensory surfaces. The early corpus callosum may have also served as a substrate for growth of fibers connecting higher-order areas, which possibly participated in the propagation of neuronal ensembles of synchronized activity between the hemispheres. However, as brains became much larger, the increasingly longer interhemispheric distance may have worked as a constraint for efficient callosal transmission. Callosal fiber composition tends to be quite uniform across species with different brain sizes, suggesting that the delay in callosal transmission is longer in bigger brains. There is only a small subset of large-diameter callosal fibers whose size increases with increasing interhemispheric distance. These limitations in interhemispheric connectivity may have favored the development of brain lateralization in some species like humans. "...if the currently received statements are correct, the appearance of the corpus callosum in the placental mammals is the greatest and most sudden modification exhibited by the brain in the whole series of vertebrated animals..." T.H. Huxley (1).