Subtraction images: A really helpful tool in non-vascular MRI

Early Bone Ischemia in Pediatric Acute Hematogenous Osteomyelitis and its Association With Progression to Chronic Osteomyelitis: New Insights From Gadolinium-enhanced Subtraction MRI

BACKGROUND

Acute hematogenous osteomyelitis (AHO), the most common osteoarticular infection in children, carries a significant risk for chronic complications. Predicting chronic complications early in the course of disease is challenging. The underlying pathogenesis of complications is not fully understood.

METHODS

Children who presented to Sultan Qaboos University Hospital, Muscat, Oman between January 2015 and April 2022 for AHO were identified by a search of magnetic resonance imaging (MRI) records. Children between 1 month and 18 years of age who did not meet exclusion criteria, and whose MRI also included gadolinium-enhanced subtraction (GES) sequences were included in the analysis. Outcomes were compared between patients who showed early evidence of bone ischemia and those who did not.

RESULTS

The analysis included 11 children who had GES MRI sequences from among 18 AHO cases in total. Median age was 5 years (IQR, 4-9), and 82% were males. Median duration of symptoms at presentation was 5 days (IQR, 3-7). GES sequences showed early bone ischemia in 6 of 11 (55%) patients. Patients with early bone ischemia were treated with significantly longer durations of IV antibiotics (median 23 vs. 10 days, P = 0.017) and oral antibiotics (median 134 vs. 29 days, P = 0.004), and required more surgical debridements (median 3 vs. 0 debridements, P = 0.017). Chronic osteomyelitis only developed among patients with early bone ischemia (5/6 vs. 0/5, P = 0.015).

CONCLUSIONS

In pediatric AHO, GES MRI sequences revealed early bone ischemia in a significant proportion of patients. Early bone ischemia was strongly associated with progression to chronic osteomyelitis.

Magnetic Resonance Imaging as the Primary Imaging Modality in Children Presenting with Inflammatory Nontraumatic Atlantoaxial Rotatory Subluxation

Inflammatory nontraumatic atlantoaxial rotatory subluxation (AAS) in children is an often-missed diagnosis, especially in the early stages of disease. Abscess formation and spinal cord compression are serious risks that call for immediate surgical attention. Neither radiographs nor non-enhanced computed tomography (CT) images sufficiently indicate inflammatory processes. Magnetic resonance imaging (MRI) allows a thorough evaluation of paraspinal soft tissues, joints, and ligaments. In addition, it can show evidence of vertebral distraction and spinal cord compression. After conducting a scoping review of the literature, along with scientific and practical considerations, we outlined a standardized pediatric MRI protocol for suspected inflammatory nontraumatic AAS. We recommend contrast-enhanced MRI as the primary diagnostic imaging modality in children with signs of torticollis in combination with nasopharyngeal inflammatory or ear nose and throat (ENT) surgical history.

Usefulness of subtraction pelvic magnetic resonance imaging for detection of ovarian endometriosis

Background

To minimize damage to the ovarian reserve, it is necessary to evaluate the follicular density in the ovarian tissue surrounding endometriosis on preoperative imaging. The purpose of the present study was to evaluate the usefulness of subtraction pelvic magnetic resonance imaging (MRI) to detect ovarian reserve.

Methods

A subtracted T1-weighted image (^subT1WI) was obtained by subtracting unenhanced T1WI from contrast-enhanced T1WI (^ceT1WI) with similar parameters in 22 patients with ovarian endometriosis. The signal-to-noise ratio (SNR) in ovarian endometriosis, which was classified into the high signal intensity and iso-to-low signal intensity groups on the T2-weighted image, was compared to that in normal ovarian tissue. To evaluate the effect of contrast enhancement, a standardization map was obtained by dividing ^subT1WI by ^ceT1WI.

Results

On visual assessment of 22 patients with ovarian endometriosis, 16 patients showed a high signal intensity, and 6 patients showed an iso-to-low signal intensity on T1WI. Although SNR in endometriosis with a high signal intensity was higher than that with an iso-to-low signal intensity, there was no difference in SNR after the subtraction (13.72±77.55 vs. 63.03±43.90, p=0.126). The area of the affected ovary was smaller than that of the normal ovary (121.10±22.48 vs. 380.51±75.87 mm², p=0.002), but the mean number of pixels in the viable remaining tissue of the affected ovary was similar to that of the normal ovary (0.53±0.09 vs. 0.47±0.09, p=0.682).

Conclusion

The subtraction technique used with pelvic MRI could reveal the extent of endometrial invasion of the normal ovarian tissue and viable remnant ovarian tissue.

Diffusion-weighted imaging in hemorrhagic abdominal and pelvic lesions: restricted diffusion can mimic malignancy

Diffusion-weighted imaging (DWI) is an increasingly utilized sequence in the assessment of abdominal and pelvic lesions. Benign lesions containing hemorrhagic products, with conglomerates of tightly packed blood cells or fibers, can have restricted water diffusion on DWI and apparent diffusion coefficient maps. Such lesions can have restricted diffusion erroneously attributed to malignancy. This review illustrates benign hemorrhagic lesions displaying restricted diffusion, with histopathologic correlation in relevant cases.