Extra-Cranial Applications of Diffusion-Weighted MRI

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The myometrium and endometrium differ in terms of their ADC values throughout the menstrual cycle and menopause. In the endometrium, ADC values are lower in the menstrual phase and in menopausal women, whereas they are higher in the proliferative phase and even higher in the secretory phase.

Diffusion-weighted imaging in the CNS

In the myometrium, ADC values are lower in menopausal women and in the proliferative phase, whereas they are higher in the secretory phase and even higher in the menstrual phase. The ADC values are also different for women using oral contraceptives, the myometrium showing higher ADC values in women who take oral contraceptives than in women of reproductive age who do not 17 , DWI is now widely used for the assessment and staging of endometrial and cervical neoplasms, which tend to show typical restriction patterns 3 , 4 , 6 , However, radiologists should be aware of some potential pitfalls of using DWI to evaluate the uterus, exercising caution in order to avoid mistaking benign conditions for malignancy.

Leiomyomas, the most common myometrial tumors, are benign tumors that are usually easily diagnosed on MRI. They appear as well-circumscribed nodules that are hypointense on T2W and T1-weighted T1W images 3 , 13 , 19 , This can be confusing because, as we mentioned above, dark ADC lesions can be considered suspicious. The cellular leiomyoma type, which is composed of densely cellular fascicles of smooth muscle with little intervening collagen, deserves particular attention.

Cellular leiomyoma shows few mitotic figures and little or no cytological atypia. Due to its high cellularity, this type of leiomyoma does not show the classic MRI features on morphological sequences and can show an increased signal on T2W images 4 , 6 , 19 , 20 , In rare cases, a leiomyoma can undergo sarcomatous transformation into a leiomyosarcoma, the most common malignant tumor of the myometrium 4 , 6 , 19 , Leiomyosarcomas appear as large heterogeneous tumors, infiltrating the adjacent myometrium, with intermediate to high SI on T2W images and low to intermediate SI on T1W images 3 , 4 , 6.

Therefore, there is significant imaging overlap between cellular leiomyomas and leiomyosarcomas, which means that neither morphological sequences nor DWI are able to exclude malignancy 3 , 4 , 6 , 7 , 13 , Radiologists should be aware of the fact that normal ovaries can have a relative high SI on DWI sequences at any b value, especially during the luteal phase. In addition, follicle cysts which can reach up to 5 cm in diameter can present with high SI in all DWI sequences, even those with high b values, and concomitant high SI on the ADC map-i.

When it comes to adnexal lesions, transvaginal ultrasound continues to be the first-line imaging modality, because it is affordable, is fast, and efficiently characterizes most such lesions 4 - 6 , 8 , 9 , 19 , 25 - However, MRI plays a vital role in the characterization and surgical planning of lesions classified as indeterminate on ultrasound 3 , 8 , 9 , 19 , 27 - 29 , 32 , DWI has been widely included in MRI protocols and has increased the accuracy for malignancy detection.

Whereas ovarian malignancies tend to show solid areas with intermediate SI on T2W images and restricted diffusion, benign ovarian tumors are more likely to exhibit low SI on T2W images and low SI at high b values. Thomassin-Naggara et al.

There is an overlap between benign and malignant ovarian tumors-restricted diffusion is not exclusive of malignant lesions. Features characteristic of malignancy on DWI can be seen in patients with ovarian torsion, abscess, endometrioma, hemorrhagic cyst, mature cystic teratoma, and non-edematous fibroma, thus creating potential pitfalls 3 , 6 , 13 , 20 , 21 , 25 , 29 , 33 - Ovarian torsion is a serious cause of lower abdominal pain that can occur at any age, although it is more common in women of reproductive age.

The torsion initially causes venous stasis, which can progress to arterial stasis because of the edema. Complete arterial torsion results in hemorrhagic, gangrenous necrosis 34 - Transvaginal ultrasound with Doppler flow study is the first-line imaging modality when ovarian torsion is suspected 25 , However, although the absence of flow on Doppler is highly suggestive of ovarian torsion, its presence does not exclude disease, because the ovaries have dual arterial supply Therefore, ovarian torsion can be a challenging diagnosis to make with ultrasound, particularly in subacute or intermittent cases; as such, MRI may be required for better evaluation 25 , 35 , Gadolinium-enhanced sequences are helpful, and the absence of parenchymal enhancement is a clue for the diagnosis 32 , 34 , In the affected ovary, hemorrhagic infarction, cytotoxic cellular edema, and blood clots from venous thrombosis cause restricted diffusion, with high SI at high b values and low ADCs 21 , 25 , 34 - Tubo-ovarian abscess is a condition within the wide spectrum of pelvic inflammatory disease 26 , 32 , Morphological MRI usually shows a complex cystic mass with ill-defined borders, thickened walls, and thickened septa, with low SI on T1W images and heterogeneously high SI on T2W images, which enhance after gadolinium-based contrast administration Figure 4.

There are studies-such as those conducted by Li et al. The content of a tubo- ovarian abscess is pus-a viscous fluid that consists of bacteria, inflammatory cells, cellular debris, necrotic tissue with coagulative necrosis , and proteinaceous plasma with high cellularity. Therefore, the higher the viscosity of the pus is, the higher will be the SI in DWI Figure 4 and the lower will be the SI on the ADC map-although the restricted diffusion may be misleading, the lack of contrast enhancement indicates that it is pus and not a solid mass 5 , 7 , 14 , 16 , 19 , 25 - 27 , 38 - Consequently, when an area with restricted diffusion is depicted in the adnexa of a symptomatic patient with acute pelvic pain and fever, with simultaneous high to intermediate SI on T2W images and no enhancement after contrast administration, it is very likely an abscess 12 , Nevertheless, false negatives can occur in cases of chronic abscess, abscesses smaller than 1 cm in diameter, and abscesses under antibiotic therapy Although transvaginal ultrasound can be useful in the diagnosis of ovarian endometrioma, MRI has been shown to have higher specificity 15 , 31 , On MRI, endometrioma typically appears as a cystic lesion with high SI on T1W images Figure 5 , with or without selective fat suppression, and relatively low SI on T2W images-the shading sign, which has been historically used to diagnose endometriomas 31 , 32 , However, that sign is not exclusive to endometriomas, and the "T2 dark spot" sign-consisting of T2 dark spots representing chronically retracted clots with high protein and hemoglobin content that exhibit T2 shortening-can therefore be useful in their diagnosis 31 , Because that can hamper the detection of malignant transformation, correlation with other sequences, either morphological or contrast-enhanced, is helpful whenever malignancy is suspected.

Hemorrhagic cysts occur due to hemorrhage within a functional cyst and tend to reabsorb spontaneously. On MRI, there are typical features that allow the diagnosis of these tumors without biopsy. Their sebaceous content has high SI on T1W images, similar to that of retroperitoneal fat, becoming hypointense after selective fat suppression-that unique characteristic can be sufficient to establish its diagnosis 13 , 19 , 32 , 42 , Sala et al.

In rare cases, mature cystic teratoma can undergo malignant transformation and therefore show true restricted diffusion. The morphological correlation is mandatory, because malignant parietal nodules tend to show intermediate SI on T2W images and enhancement after gadolinium administration 3 , 13 , 30 , Fibromas are the most common ovarian sex cord-stromal tumors, occurring in premenopausal and postmenopausal women 32 , They are benign, have no theca cells, and do not exhibit estrogenic activity-being composed of whorled bundles of spindle-shaped fibroblasts and collagen They appear as solid masses and usually have a diameter of less than 10 cm.

However, they can be quite large and can therefore resemble malignant neoplasms 25 , Non-edematous fibromas are composed of dense stromal proliferation and do not undergo edematous degeneration-which can occur in large fibromas 22 , When they reach large dimensions, fibromas can be misdiagnosed as pedunculated subserosal uterine or broad-ligament leiomyomas This pitfall can be avoided by assessing the very dark signal on T2W images.

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That can lead to a false-positive diagnosis of malignancy, and the solution to overcome this potential pitfall is to compare DWI sequences with contrast-enhanced fat-suppressed T1W images, in which only solid tumor components will enhance. On axial images, it can appear as a complete or incomplete bright ring behind the uterus-this can be potentially confusing, and DWI findings must be correlated with those of the morphological MRI sequences 12 , 14 , Karaarslan E, Arslan A.

Diffusion weighted MRI in non-infarct lesions of the brain. Eu J Radiol. Role of diffusion weighted MR imaging in early diagnosis of cerebral infarction. Ind J Radiol Image. Diffusion-weighted MR imaging: diagnostic accuracy in patients imaged within 6 hours of stroke symptom onset. Diffusion-weighted MR imaging in hypertensive encephalopathy: clues to pathogenesis. Am J Neuroradiol. Variability of the major cerebral arteries.

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J Neurosurg. Diffusion weighted MR imaging of the brain. Early assessment of severe hypoxic-ischemic encephalopathy in neonates by diffusion-weighted magnetic resonance imaging techniques and its significance. Chin J Ped. Diffusion weighted MRI in brain tumour. Neuroimaging Clin. Diffusion weighted MR images of intracerebral masses: comparison with conventional MR. Increased water self-diffusion in chronic plaques and in apparently normal white matter in patients with multiple sclerosis. Target Volume Delineation and Field Setup.

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