MR imaging fails to detect bone marrow oedema in osteomyelitis: report of two cases

MR characteristics of mucinous tubular and spindle cell carcinoma (MTSCC) of the kidney: comparison with clear cell and papillary subtypes of renal cell carcinoma

PURPOSE

To describe MR features of mucinous tubular spindle cell carcinoma (MTSCC) of the kidney that may help differentiate from clear cell renal cell carcinoma (ccRCC) and papillary RCC (pRCC).

METHODS

15 MTSCCs were retrospectively evaluated by MR with T2-weighted image without fat suppression (n = 15) and dynamic contrast-enhanced (DCE), fat-suppressed T1-weighted GRE (n = 11). Size-matched ccRCC (n = 30) and pRCC (n = 30) were evaluated as control. T2 ratio was calculated as the signal intensity (SI) ratio of the lesion to the renal cortex on T2W images. Enhancement ratio (ER) was calculated as (SI_post - SI_pre)/(SI_pre), where SI_pre (SI_post) is the SI of the entire lesion on each phase of DCE images. Early nodular enhancement was subjectively evaluated in MTSCC. T2 ratio and ER were compared using the Mann-Whitney U test with Bonferroni correction.

RESULTS

The mean value of T2 ratio was highest in ccRCC (1.24), followed by MTSCC (1.02), and pRCC (0.84). Difference of T2 ratio was significant between ccRCC and pRCC (p < 0.001), but not between MTSCC and ccRCC (p = 0.4) or between MTSCC and pRCC (p = 0.2). The mean ER of MTSCC, ccRCC and pRCC were 1.33, 1.53 and 0.38 in corticomedullary phase (CMP), 1.60, 1.61 and 0.69 in nephrographic phase (NGP) and 1.79, 1.35 and 0.77 in excretory phase (EP), respectively. ERs were significantly different between MTSCC and pRCC in CMP (p = 0.01), NGP (p = 0.003), and EP (p = 0.002). Early nodular enhancement was observed in 4/11 MTSCC (36%), 17/30 ccRCC (57%), and 2/30 pRCC (7%).

CONCLUSIONS

MTSCC has distinct MR features that can help differentiate from ccRCC and pRCC. MTSCC enhances more avidly compared to pRCC and shows gradual progressive enhancement.

Hemosiderin deposition in papillary renal cell carcinoma and its potential to mask enhancement on MRI: analysis of 110 cases

OBJECTIVES

To evaluate the relationship between imperceptible T1 enhancement of papillary renal cell carcinoma (pRCC) on MR and intratumoral hemosiderin deposition.

METHODS

One hundred ten pRCCs (≤ 7 cm) were evaluated by MR with in- and opposed-phase spoiled gradient echo (GRE) and T1-weighted spoiled GRE with fat suppression before and after contrast. Hemosiderin deposition was assessed by SI_index and D_index on in- and opposed-phase images. SI_index and D_index are calculated as (SI_in - SI_opp)/(SI_in) × 100, where SI_in and SI_opp are tumor signal intensities on in- and opposed-phase images and (D_in)/(D_opp), where D_in and D_opp are tumor diameters on in- and opposed-phase images, respectively. The degree of tumor enhancement was classified as grade 1 (no), grade 2 (subtle), or grade 3 (definite). Tumor enhancement on CT was assessed when available.

RESULTS

Five (5%), 10 (9%), and 95 (86%) tumors were categorized as grades 1, 2, and 3 enhancement, respectively. The mean SI_index was - 33.9, - 25.3, and 1.00, whereas the mean D_index was 1.26, 1.05, and 1.00 in tumors with grades 1, 2, and 3 enhancement, respectively. Tumors with grade 1 enhancement had significantly lower SI_index (p = 0.001) and higher D_index (p = 0.005) than those with grade 3 enhancement. Among six tumors with grade 1 or 2 enhancement and available CT, four tumors showed > 20 HU enhancement.

CONCLUSIONS

pRCC with no subjective enhancement on contrast-enhanced MR showed hemosiderin deposition evident by lower SI_index and higher D_index. Hemosiderin deposition might mask the tumor enhancement on MR.

KEY POINTS

• 5% of papillary renal cell carcinoma showed imperceptible enhancement on contrast-enhanced MR. • Hemosiderin deposition in papillary renal cell carcinoma might mask the tumor enhancement on contrast-enhanced MR due to T2/T2*-shortening effects. • A renal lesion with extensive hemosiderin deposition but no perceptible enhancement on MR should be considered suspicious for papillary renal cell carcinoma.

Detection of pediatric musculoskeletal pathology using the fluid-sensitive sequence

BACKGROUND

Musculoskeletal complaints are common among children, and magnetic resonance (MR) is increasingly used to supplement the clinical assessment. The validation of a short triage protocol could reduce the number of unnecessary contrast-enhanced MR studies that sometimes also require the need for sedation.

OBJECTIVE

To compare the diagnostic accuracy between fluid-sensitive sequence and contrast-enhanced MR study in the detection of musculoskeletal pathology in the pelvis and the appendicular skeleton in children older than 2 years.

MATERIALS AND METHODS

We performed a retrospective review between Feb. 1, 2016, and Oct. 31, 2016, and identified 99 studies from 96 patients (48 boys and 48 girls; mean age ± standard deviation, 11.1±4.6 years) without syndromic deformity, recent trauma, a history of infectious or inflammatory arthropathy, prior instrumentation or incomplete records. Two radiologists reviewed each study twice, at least 1 month apart, first using only the fluid-sensitive sequences (triage study) and later using the contrast-enhanced study. Readers rated the presence or absence of pathology independently and generated final impressions in consensus. We used Cohen's kappa (κ) and percentage agreement to compare agreement between readers and between studies, respectively.

RESULTS

Inter-reader agreement was overall higher for the contrast-enhanced studies (κ range = 0.91-1) than for the triage studies (κ range = 0.49-1). Percentage agreement between studies was high for the detection of pathology (97-100%) and for the impressions (93%). Clinical diagnoses were stress reaction or overuse in 31%, infection in 21%, space-occupying process in 17%, normal in 15%, inflammatory in 14%, and both inflammatory and overuse in 1%. The full study increased diagnostic confidence in five studies and accuracy in two but did not alter management.

CONCLUSION

The fluid-sensitive sequence had a near-perfect percentage of agreement with the contrast-enhanced study in the detection of musculoskeletal pathology and could possibly be used to screen children who need a contrast-enhanced MR study.

MR imaging of infectious processes of the knee

Infectious processes about the knee can result from the hematogenous spread of infection, spread from a contiguous source, direct implantation of pathogens, and prior surgery. Soft tissues, joints, and bones can be infected by bacteria, fungi, parasites, or viruses. MR imaging is useful in identifying cellulitis, abscess, septic arthritis, and osteomyelitis. The inherent tissue contrast provided by MR imaging allows for the delineation of soft-tissue infection and osteomyelitis. Therefore, MR imaging is a useful tool in evaluating the extent of infection, and in facilitating adequate debridement and drainage. MR imaging is particularly useful in the setting of chronic posttraumatic osteomyelitis and in prior surgical procedures, such as arthroscopy, anterior cruciate ligament reconstruction, and amputation.

MR Imaging of Infectious Processes of the Knee

Infectious processes about the knee can result from the hematogenous spread of infection, spread from a contiguous source, direct implantation of pathogens, and prior surgery. Soft tissues, joints, and bones can be infected by bacteria, fungi, parasites, or viruses. MR imaging is useful in identifying cellulitis, abscess, septic arthritis, and osteomyelitis. The inherent tissue contrast provided by MR imaging allows for the delineation of soft-tissue infection and osteomyelitis. Therefore, MR imaging is a useful tool in evaluating the extent of infection, and in facilitating adequate debridement and drainage. MR imaging is particularly useful in the setting of chronic posttraumatic osteomyelitis and in prior surgical procedures, such as arthroscopy, anterior cruciate ligament reconstruction, and amputation.

Perthes' disease in the very young child

We report two cases of very young children who presented with irritable hips and in whom magnetic resonance imaging with gadolinium-enhancement revealed ischaemic changes affecting the capital ossific nucleus. Radiological changes consistent with Perthes' disease subsequently appeared. In the published literature Perthes' disease has been reported in children as young as 24 months. Gadolinium-enhanced magnetic resonance imaging has revealed Perthes' disease in younger children which can predate the appearance of radiographic changes by up to 3 months.

Imaging of osteomyelitis in children

Imaging approach to osteomyelitis in children should aim toward a timely and accurate diagnosis in view of the need for prompt therapy to prevent sequelae. One must take advantage of the specific value of each imaging modality and adopt a strategy that works best for a given child in a given institution.