Alternative diagnoses at paediatric appendicitis MRI.

As the utilization of MRI in the assessment for paediatric appendicitis increases in clinical practice, it is important to recognize alternative diagnoses as the cause of abdominal pain. The purpose of this review is to share our institution's experience using MRI in the evaluation of 510 paediatric patients presenting with suspected appendicitis over a 30 month interval (July 2011 to December 2013). An alternative diagnosis was documented in 98/510 (19.2%) patients; adnexal pathology (6.3%, n = 32), enteritis-colitis (6.3%, n = 32), and mesenteric adenitis (2.2%, n = 11) comprised the majority of cases. These common entities and other less frequent illustrative cases obtained during our overall institutional experience with MRI for suspected appendicitis are reviewed.

Metaphyseal fractures mimicking abuse during treatment for clubfoot.

BACKGROUND: Metaphyseal injuries resembling the classic metaphyseal lesion (CML) of abuse may occur as the result of serial casting during treatment of clubfoot deformity. Mentioned in the orthopedic literature in 1972, this iatrogenic fracture has not been described in the radiologic literature nor has the similarity to injuries occurring with abuse been previously recognized. OBJECTIVE: To describe the mechanism and radiographic appearance of metaphyseal injury observed during serial casting of clubfoot. Note similarities to the CML of abuse. MATERIALS AND METHODS: Eight children ranging in age from 1 to 4 months underwent casting for clubfoot. Five orthopedic surgeons from three different institutions performed the casting. Two patients had spina bifida and one, arthrogryposis. A complete skeletal survey was performed on one child who was abused; there was no suspicion of abuse in the remaining seven. RESULTS: All children manifest injury with periosteal new bone. One child had clear evidence of abuse with 24 rib fractures. X-rays of lower extremities in short leg casts revealed bilateral tibial metaphyseal fractures. Four other children had metaphyseal fractures resembling the CML of abuse, and three developed an area of sclerosis within the metaphysis. CONCLUSION: In the setting of serial casting for equinovarus deformity, metaphyseal injury even the CML of abuse may be noted. Since inflicted injuries are almost always unobserved and explanations rarely offered, the fact that the CML occurs as a result of orthopedic maniuplation may offer some further insight concerning the pathogenesis of this well-described abuse injury.

Hemoperitoneum and disseminated intravascular coagulation in two neonates with congenital bilateral neuroblastoma.

We report two neonates with anemia, hemoperitoneum, and bilateral palpable abdominal masses. Both developed bleeding: a hemoperitoneum in one and visceral hemorrhages secondary to disseminated intravascular coagulation in the other. Each child was thought to have an unusual complication of adrenal hemorrhage, as the masses were of mixed echogenicity. However, histological evaluation revealed neuroblastoma. These cases point out the diagnostic dilemma of a mixed echogenicity suprarenal mass in the neonatal period and emphasize that local and disseminated bleeding can occur as a major manifestation of neuroblastoma.

Avascular necrosis after treatment of DDH: the protective influence of the ossific nucleus.

We retrospectively reviewed the results of open or closed reduction for developmental dysplasia of the hip (DDH) in 49 children younger than 12 months old, who had 57 hip dislocations. Group A (18 hips) developed partial or complete avascular necrosis (AVN), and group B (39 hips) did not develop AVN. Thirty-eight hips were treated by closed reduction, and 17 had open reduction. One patient with bilateral hip dislocation initially had closed reductions followed by bilateral open reduction 3 months later. With the numbers available for study, there was no significant difference in the occurrence of AVN with respect to variables such as preliminary traction, closed versus open reduction, Pavlik harness use, and age at the time of operative intervention. However, the presence of the ossific nucleus before reduction, detected either by radiographs (p < 0.001) or ultrasonography (p = 0.033) was statistically significant in predicting AVN. Only one (4%) of 25 hips with an ossific nucleus developed AVN, whereas 17 (53%) of 32 hips without an ossific nucleus before reduction developed AVN. Our results suggest that the presence of the ossific nucleus before closed or open reduction for DDH may decrease the risk of AVN.

Simulations of the erythrocyte cytoskeleton at large deformation. I. Microscopic models.

Three variations of a polymer chain model for the human erythrocyte cytoskeleton are used in large deformation simulations of microscopic membrane patches. Each model satisfies an experimental observation that the contour length of the spectrin tetramers making up the erythrocyte cytoskeleton is roughly square root of 7 times the end-to-end distance of the tetramer in vivo. Up to modest stress, each brushy cytoskeletal network behaves, consistently, like a low-temperature, planar network of Hookean springs, with a model-dependent effective spring constant, keff, in the range of 20-40 kBT/s(o)2, where T is the temperature and s(o) is the force-free spring length. However, several features observed at large deformation distinguish these models from spring networks: 1) Network dimensions do not expand without bound in approaching a critical isotropic tension (square root of 3 keff) that is a characteristic limit of Hookean spring nets. 2) In surface compression, steric interactions among the chain elements prevent a network collapse that is otherwise observed in compression of planar triangulated networks of springs. 3) Under uniaxial surface tension, isotropy of the network disappears only as the network is stretched by more than 50% of its equilibrium dimensions. Also found are definitively non-Hookean regimes in the stress dependence of the elastic moduli. Lastly, determinations of elastic moduli from both fluctuations and stress/strain relations prove to be consistent, implying that consistency should be expected among experimental determinations of these quantities.

Simulations of the erythrocyte cytoskeleton at large deformation. II. Micropipette aspiration.

Coarse-grained molecular models of the erythrocyte membrane's spectrin cytoskeleton are presented in Monte Carlo simulations of whole cells in micropipette aspiration. The nonlinear chain elasticity and sterics revealed in more microscopic cytoskeleton models (developed in a companion paper; Boey et al., 1998. Biophys. J. 75:1573-1583) are faithfully represented here by two- and three-body effective potentials. The number of degrees of freedom of the system are thereby reduced to a range that is computationally tractable. Three effective models for the triangulated cytoskeleton are developed: two models in which the cytoskeleton is stress-free and does or does not have internal attractive interactions, and a third model in which the cytoskeleton is prestressed in situ. These are employed in direct, finite-temperature simulations of erythrocyte deformation in a micropipette. All three models show reasonable agreement with aspiration measurements made on flaccid human erythrocytes, but the prestressed model alone yields optimal agreement with fluorescence imaging experiments. Ensemble-averaging of nonaxisymmetrical, deformed structures exhibiting anisotropic strain are thus shown to provide an answer to the basic question of how a triangulated mesh such as that of the red cell cytoskeleton deforms in experiment.

Entropy-driven instability and rupture of fluid membranes.

A computer simulation is used to investigate hole formation in a model membrane. The model parameters are the stress applied to the membrane, and the edge energy per unit length along the hole boundary (edge tension). Even at zero stress, the membrane has an entropically driven instability against hole formation. Within the model, the minimum edge tension required for the stability of a typical biological membrane is in the region of 1 x 10(-11) J/m, which is similar to the edge tension obtained in many measurements of biomembranes. At the zero-stress instability threshold, the hole shape is the same as a self-avoiding ring, but under compression, the hole shape assumes a branched polymer form. In the presence of large holes at zero stress, the membrane itself behaves like a branched polymer. The boundaries of the phase diagram for membrane stability are obtained, and general features of the rate of membrane rupture under stress are investigated. A model in which the entropy of hole formation is proportional to the hole perimeter is used to interpret the simulation results at small stress near the instability threshold.

Barrier-free paths of directed protein motion in the erythrocyte plasma membrane.

A model is presented for the steric interaction between a plasma membrane protein and the membrane cytoskeleton in the human erythrocyte. The cytoskeleton is treated as a network of polymer chains attached to a flat bilayer, and the membrane protein is a hemisphere of effective radius R(e) with center on the bilayer edge. The simulation is used to investigate the barrier-free path L for linear guided motion of a protein in the bilayer plane. It is shown that the barrier-free paths of small proteins can be used to extract the effective in-plane diameter of cytoskeletal components. For example, the in-plane diameter of an ankyrin attachment site is found to be approximately 12 nm in the simulation, or twice the computational spectrin diameter. The barrier-free paths of large proteins (R(e) > 23 nm) vanish when the proteins are corralled by the cytoskeleton. For intermediate size proteins, L decreases approximately as L is directly proportional to S-1.4 where S is proportional to the sum of the protein and cytoskeleton chain radii.

Optimal cost-effective timing of cranial ultrasound screening in low-birth-weight infants.

Our aim in this study was to determine whether delaying the initial screening cranial ultrasound on infants of low birth weight until the 2nd week of life affects clinical diagnosis and cost of patient care. Data were reviewed on all premature infants of less than 33 weeks gestation or less than 1500 g birth weight admitted to the Neonatal Intensive Care Unit between January 1989 and August 1992. Babies admitted before August 1991 were screened on day 4 or 5 with a second scan frequently performed on day 14; babies admitted after that date were screened once between days 10-14. Populations were compared for (1) proportion of ultrasound findings considered normal on final diagnosis; (2) incidence of major and minor abnormalities; (3) periventricular leukomalacia (PVL); (4) change in diagnosis from 1st to 2nd week; and (5) number of studies performed per patient. The study group was composed of 499 eligible infants. Demographic features of infants screened in the 1st vs. 2nd week of life were similar, with comparable diagnoses of major and minor intracranial hemorrhage and ventricular dilatation; however, more patients screened in the 1st week had questionable PVL diagnosed (p = 0.04). There was a significant decrease in the number of scans per patient in the group screened in the 2nd week (p < 0.004). Routine screening may be delayed until the 2nd week without compromising patient care. Widespread use of a similar screening protocol would result in significantly fewer studies being performed, with an estimated saving, in the USA, of more than $3 million annually.

Role of apnea in nonaccidental head injury.

We hypothesize that apnea induced by shaking or by shaking combined with impact plays a major role in the pathophysiology of nonaccidental head trauma and accounts for the poor outcome in this subgroup of patients. In a retrospective study of 28 children who suffered significant nonaccidental head injury, 57% had a history of apnea prior to hospitalization, 82% were intubated upon admission, and 71% had early seizures. For further evidence of ischemia and hypoxia, the first recorded blood pressure was < 80 in 50% and the arterial pH < 7.3 in 54%. Seventy-one percent had diffuse brain swelling which is characteristic of cerebral hypoxia and/or ischemia on the first CT scan. None of the children who had clinical evidence of cerebral hypoxia or ischemia had a good outcome. We conclude that trauma-induced apnea causes cerebral hypoxia and/or ischemia which is more fundamental to outcome than the mechanism of injury (shaken vs. shaken with impact), subdural hemorrhage, subarachnoid hemorrhage, diffuse axonal injury, parenchymal shear, or brain contusion.

Tc-99m MAG3 renography in renal vein thrombosis secondary to Finnish-type congenital nephrotic syndrome.

Scintigraphic findings in renal vein thrombosis (RVT) have been well described on studies performed with Tc-99m DPTA, Tc-99m glucoheptonate, and I-131 orthoiodohippurate. The authors could find no reports of RVT findings on Tc-99m mercaptoacetyltriglycine (MAG3) imaging. Tc-99m MAG3 renal scintigraphy in an infant with RVT because of Finnish-type congenital nephrotic syndrome is described. Correlative ultrasound and inferior vena cava venogram findings are presented.

Computer simulation of a model network for the erythrocyte cytoskeleton.

The geometry and mechanical properties of the human erythrocyte membrane cytoskeleton are investigated by a computer simulation in which the cytoskeleton is represented by a network of polymer chains. Four elastic moduli as well as the area and thickness are predicted for the chain network as a function of temperature and the number of segments in each chain. Comparisons are made with mean field arguments to examine the importance of steric interactions in determining network properties. Applied to the red blood cell, the simulation predicts that in the bilayer plane the membrane cytoskeleton has a shear modulus of 10 +/- 2 x 10(-6) J/m2 and an areal compression modulus of 17 +/- 2 x 10(-6) J/m2. The volume compression modulus and the transverse Young's modulus of the cytoskeleton are predicted to be 1.2 +/- 0.1 x 10(3) J/m3 and 2.0 +/- 0.1 x 10(3) J/m3, respectively. Elements of the cytoskeleton are predicted to have a mean displacement from the bilayer plane of 15 nm. The simulation agrees with some, but not all, of the shear modulus measurements. The other predicted moduli have not been measured.

Fetal rhabdomyoma and nevoid basal cell carcinoma syndrome.

A 6-year-old white female presented with a fetal rhabdomyoma of the posterior mediastinum and retroperitoneum. Radiologic evaluation and family history revealed features of the nevoid basal cell carcinoma syndrome (NBS). Literature review disclosed two other children with NBS and fetal rhabdomyoma, which should be regarded as one of the soft tissue tumors associated with NBS.

CT and MR imaging of the pediatric orbit.

Orbital abnormalities encountered in the pediatric population differ substantially from those found in adult patients. Retinoblastoma, the most serious intraocular tumor, is often difficult to diagnose, but use of computed tomography (CT) (which reveals the characteristic focal calcification) and magnetic resonance (MR) imaging allows this tumor to be differentiated from pseudogliomas, such as Coats disease, and retrolental fibroplasia. CT and MR imaging help in the differentiation of orbital cellulitis from preseptal, lacrimal, and eyelid infectious processes and of orbital pseudotumor from Graves disease. In cases of orbital trauma, CT is excellent for detecting orbital fractures and metallic foreign bodies; MR imaging is better for depicting ocular and optic nerve injuries. Both modalities allow the differentiation of rhabdomyosarcoma from dermoid, cavernous hemangioma, and lymphangioma and provide helpful information for the diagnosis of many other tumors. Since CT and MR imaging have widely expanded the capabilities of orbital imaging, it is more important than ever before for radiologists to understand pediatric orbital disease.

Rickets--a complication of ifosfamide chemotherapy for Wilms tumor.

Recent reports of metabolic bone disease occurring as a result of drug induced Fanconi syndrome due to ifosfamide have appeared in the pediatric literature. Ifosfamide is a chemotherapeutic agent used for treatment of pediatric solid tumors. We present an additional case of ifosfamide induced rickets, the first in the radiologic literature.

Focal fatty infiltration of the liver in a healthy child.

Fatty infiltration of the liver may occur in healthy children. The ultrasonographic, CT, and MRI findings are identical to those already described in the adult population.