Nuances of the unenhanced abdominal CT: careful inspection discloses critical findings

Enhancing the Interpretation of Unenhanced Abdominopelvic CT

Unenhanced abdominopelvic CT is frequently performed in patients who are critically ill or have contraindications to intravenous contrast. These cases can be challenging to interpret for the radiologist. Attention to CT physics and care in optimizing image viewing through techniques such as windowing can maximize diagnostic yield. In this case-based review, we will discuss the CT physics concepts of attenuation, common indications and reasons for unenhanced abdominopelvic CT, and review its utility through a series of illustrative cases.

CT of acute abdominopelvic hemorrhage: protocols, pearls, and pitfalls

Abdominal and pelvic hemorrhage may be secondary to a number of causes and is often a medical emergency. Patient presentation ranges from obvious trauma with evidence of hemodynamic instability to vague symptoms. CT has become the imaging modality of choice for identifying abdominopelvic hemorrhage. Recognizing acute hemorrhage as well as identifying its location and severity are key to expediting management. In the Emergency Department, ultrasound often used in the initial evaluation of trauma patients, but is not sensitive for subtle bleeds or injuries. CT is the best first-line imaging tool to identify abdominal hemorrhage and, compared with angiography, has been shown to be superior in detecting intra-abdominal bleeding, especially when the bleeding rate is low. Depending on location and etiology, abdominopelvic hemorrhage may have a characteristic appearance, such as the "sentinel clot" sign associated with blunt trauma to the solid organs or the "triangle sign" of a mesenteric bleed. The following pictorial essay reviews CT technique, study interpretation, and interpretative pearls and pitfalls in the recognition of acute abdominopelvic hemorrhage.

Low monoenergetic DECT detection of pyelonephritis extent

OBJECTIVES

To determine whether contrast enhanced DECT low monoenergetic can improve diagnostic conspicuity of inflamed kidney foci in acute pyelonephritis compared to conventional images.

MATERIALS AND METHODS

A retrospective study of 45 patients with clinical signs of acute pyelonephritis undergoing contrast-enhanced exams on a single source-DECT was conducted. Representative conventional and monoenergetic images were randomized and presented to four abdominal radiologists to determine their preference for inflamed kidney foci detection, and to determine the number of foci identified. Clinical impact of monoenergetic images was assessed using multivariant analysis. Contrast and signal to noise ratios were compared between the images using paired t-tests.

RESULTS

A greater number of foci were detected on the low energetic images for each patient (6.4 ± 5.3 vs. 4.2 ± 3.8, p < 0.02). Additionally, a consistent linear increase in the number of detected foci on the monoenergetic compared to the conventional images was seen (y = 0.10X + 0.36 R² = 0.76). Most notably, in 16% of kidneys a clearly definable focus was detected only on monoenergetic images. SNR and CNR were increased by 2 and 1.5 fold for monoenergetic compared to conventional images (p < 0.001). Monoenergetic images were preferred by all readers for detecting inflamed foci (162/180 reads, P < 0.05), with 79% interreader reliability.

CONCLUSION

Low monoenergetic images enable increased detection of inflamed kidney parenchyma, and permit identification of pathologic foci some of which were not seen on the conventional images. Along with the strong preference of radiologists, these images should be considered beneficial for evaluating acute pyelonephritis.

Evaluation and management of the surgical abdomen

PURPOSE OF REVIEW

The aim of this study was to describe important features of clinical examination for the surgical abdomen, relevant investigations, and acute management of common surgical problems in the critically ill.

RECENT FINDINGS

Lactate remains a relatively nonspecific marker of gut ischemia. Dual energy computed tomography (DECT) scan can improve diagnosis of bowel ischemia. Further evidence supports intravenous contrast during CT scan in critically ill patients with acute kidney injury. Outcomes for acute mesenteric ischemia have failed to improve over time; however, increasing use of endovascular approaches, including catheter-directed thrombolysis, may decrease need for laparotomy in the appropriate patient. Nonocclusive mesenteric ischemia remains a challenging diagnostic and management dilemma. Acalculous cholecystitis is managed with a percutaneous cholecystostomy and is unlikely to require interval cholecystectomy. Surgeon comfort with intervention based on point-of-care ultrasound for biliary disease is variable. Mortality for toxic megacolon is decreasing.

SUMMARY

Physical examination remains an integral part of the evaluation of the surgical abdomen. Interpreting laboratory investigations in context and appropriate imaging improves diagnostic ability; intravenous contrast should not be withheld for critically ill patients with acute kidney injury. Surgical intervention should not be delayed for the patient in extremis. The intensivist and surgeon should remain in close communication to optimize care.

ACR Appropriateness Criteria® Acute Pyelonephritis

Pyelonephritis refers to infection involving the renal parenchyma and renal pelvis. In most patients, uncomplicated pyelonephritis is diagnosed clinically and responds quickly to appropriate antibiotic treatment. If treatment is delayed, the patient is immunocompromised, or for other reasons, microabscesses that form during the acute phase of pyelonephritis may coalesce, forming a renal abscess. Patients with underlying diabetes are more vulnerable to complications, including emphysematous pyelonephritis in addition to abscess formation. Additionally, diabetics may not have the typical flank tenderness that helps to differentiate pyelonephritis from a lower urinary tract infection. Additional high-risk populations may include those with anatomic abnormalities of the urinary tract, vesicoureteral reflux, obstruction, pregnancy, nosocomial infection, or infection by treatment-resistant pathogens. Treatment goals include symptom relief, elimination of infection to avoid renal damage, and identification of predisposing factors to avoid future recurrences. The primary imaging modalities used in patients with pyelonephritis are CT, MRI, and ultrasound. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.