Computed Tomography With Intravenous Contrast Alone: The Role of Intra-abdominal Fat on the Ability to Visualize the Normal Appendix in Children

Background Computed tomography (CT) with enteric contrast is frequently used to evaluate children with suspected appendicitis. The use of CT with intravenous (IV) contrast alone (CT IV) may be sufficient, however, particularly in patients with adequate intra-abdominal fat (IAF). Objectives The authors aimed 1) to determine the ability of radiologists to visualize the normal (nondiseased) appendix with CT IV in children and to assess whether IAF adequacy affects this ability and 2) to assess the association between IAF adequacy and patient characteristics. Methods This was a retrospective 16-center study using a preexisting database of abdominal CT scans. Children 3 to 18 years who had CT IV scan and measured weights and for whom appendectomy history was known from medical record review were included. The sample was chosen based on age to yield a sample with and without adequate IAF. Radiologists at each center reread their site's CT IV scans to assess appendix visualization and IAF adequacy. IAF was categorized as “adequate” if there was any amount of fat completely surrounding the cecum and “inadequate” if otherwise. Results A total of 280 patients were included, with mean age of 10.6 years (range = 3.1 to 17.9 years). All 280 had no history of prior appendectomy; therefore, each patient had a presumed normal appendix. A total of 102 patients (36.4%) had adequate IAF. The proportion of normal appendices visualized with CT IV was 72.9% (95% confidence interval [CI] = 67.2% to 78.0%); the proportions were 89% (95% CI = 81.5% to 94.5%) and 63% (95% CI = 56.0% to 70.6%) in those with and without adequate IAF (95% CI for difference of proportions = 16% to 36%). Greater weight and older age were strongly associated with IAF adequacy (p < 0.001), with weight appearing to be a stronger predictor, particularly in females. Although statistically associated, there was noted overlap in the weights and ages of those with and without adequate IAF. Conclusions Protocols using CT with IV contrast alone to visualize the appendix can reasonably include weight, age, or both as considerations for determining when this approach is appropriate. However, although IAF will more frequently be adequate in older, heavier patients, highly accurate prediction of IAF adequacy appears challenging solely based on age and weight. Resumen Tomografia Computarizada Unicamente con Contraste Intravenoso: El Papel de la Grasa Intrabadominal en la Capacidad para Visualizar el Apendice Normal en los Ninos Introduction La tomografia computarizada (TC) con contraste enterico es usada frecuentemente para evaluar a los ninos con sospecha de apendicitis. El uso de la TC unicamente con contraste intravenoso (TC IV) puede ser suficiente, especialmente en pacientes con adecuada grasa intrabdominal (GIA). Objetivos 1) Determinar la capacidad de los radiologos para visualizar el apendice normal (sin enfermedad) con TC IV en ninos, y valorar si la cantidad de GIA afecta a esta capacidad; y 2) valorar la asociacion entre la idoneidad de la GIA y las caracteristicas del paciente. Metodologia Estudio retrospectivo de 16 hospitales que utilizo una base de datos prexistente de TC abdominales. Se incluyo a los ninos entre 3 y 18 anos que tenian una TC IV, una medida del peso e historia de apendectomia conocida por la revision de la historia clinica. La muestra se eligio en base a la edad con el fin de conseguir una muestra con y sin GIA adecuada. Los radiologos de cada centro releyeron las TC IV de sus centros para valorar la visualizacion del apendice y la adecuacion de la GIA. La GIA se clasifico como “adecuada” si habia cualquier cantidad de grasa completamente alrededor del ciego e “inadecuada” si era de otra manera. Resultados Se incluyeron 280 pacientes, con una media de edad de 10,6 anos (rango 3,1 a 17,9 anos). Ninguno tenia historia previa de apendectomia; por lo tanto todos los pacientes tuvieron un apendice presumiblemente normal. Ciento dos pacientes (36,4%) tuvieron GIA adecuada. El porcentaje de apendices normales visualizados con TC IV fue de 72,9% (IC 95% = 67,2% a 78,0%); la proporcion fue 89% (IC 95% = 81,5% a 94,5%), y 63% (IC 95% = 56,0% a 70,6%) en aquellos con y sin GIA adecuada (IC 95% para la diferencia de proporciones = 16% a 36%). El mayor peso y la mayor edad se asociaron fuertemente con la adecuacion de la GIA (p < 0,001), y el peso resulto ser el mayor factor predictivo, especialmente en mujeres. Aunque se asocio estadisticamente, se vio un solapamiento en los pesos y edades de aquellos con y sin GIA adecuada. Conclusiones Los protocolos que usan la TC IV para visualizar el apendice pueden razonablemente incluir el peso, la edad, o ambas como consideraciones para determinar cuando esta aproximacion es apropiada. Sin embargo, aunque la cantidad de GIA sera frecuentemente mas apropiada en los pacientes mas mayores y de mayor peso, la prediccion certera de adecuacion de GIA es altamente desafiante si se basa solo en la edad y el peso.