Clinical diagnosis
Case 251
【Discussion】
Disorder of water molecule diffusion can occur fresh infarction, tumor and abscess. ADC value of fresh infarction can decrease below 0.3, but it gradually elevates as reparative process advances. Meanwhile, tumor cell density closes extracellular free space more than surrounding healthy cell space, implying the lower ADC values on tumor. In other words, malignant tumor with highly tumor cell density lowers ADC values, comparing to benign tumor. The average ADC values on malignant tumor such as glioblastoma, metastatic liver tumor and hepatocellular carcinoma are around 1.0 (1). Of the ADC values of malignant tumors, ADC value of malignant lymphoma is the lowest, around 0.5 (2). Meanwhile, although ADC values on most benign tumor are predominantly higher than 1.2, the benign tumor with dense cellularity can be low, less than 1.0. For example, ADC value of pituitary gland adenoma is the lowest, around 0.5 (3), followed by meningioma, around 0.7 (4). Other than tumor, water molecule diffusion disorder can also occur in abscess. ADC values of abscess vary since the stage of abscess varies. Abscess is formed most by bacterial infection and neutrophils response. Abscess indicates the remnants of bacteria and immune cells. As the remain becomes more, the ADC values becomes lower; 0.2 to 0.5 (5). Namely, the ADC values on fresh abscess can become lower than malignant tumor or benign tumor and almost equal to fresh infarction.
ADC values of uterine cancer are around 1.0: squamous cell carcinoma 0.8-0.9, adenocarcinoma 0.9-1.0 (6, 7). Although water molecule diffusion is disordered on malignant tumor because of its cellularity, the ADC value on malignant tumor rarely happens to lower below 0.7 for tumor survival.
Urachal tumor is categorized into four types; umbilical urachal sinus, urachal cyst, vesico-urachal diverticulum, and patent urachus. On abscess arising from these, umbilical urachal sinus abscess occurs most followed by vesico-urachal diverticulum abscess, while malignancy occurs most arising from vesico-urachal diverticulum. ADC values of vesico-urachal carcinoma are around 1.0 while those of vesico-urachal abscess can become less than 0.7 (8, 9).
In our case, DWIMRI showed high signal intensity on urachal mass and intra-uterine lumen. ADC values were 0.51 on urachal mass and 0.37 on intra-uterine lumen, indicative of abscess on both rather than carcinoma.
The follows are the revision of description about diffusion weighted imaging (DWI) documented in Case 239.
Diffusion weighted imaging (DWI) is created by the idea of how much ability of water molecular diffusion in tissue is preserved. DWI is made based on EPI (fat saturation-T2WI) because the signal intensity of FS-T2WI on the interest lesion is high while T1WI is low, inducing easier to realize the lesion on FS-T2WI. Motion probing gradient (MPG) is given twice after 90℃ pulse and before 180℃ pulse on EPI .
MPG is given for the purpose of water molecular diffusion of the lesion is preserved or not. When water molecular diffusion is preserved such as normal tissue, signal intensity by spin echo during MPG usually drops. However, in case that water molecular diffusion in fresh infarction or dens tumor is interrupted, signal intensity does not drop so much during MPG, inducing that signal intensity remains and can be emphasized on FS-T2WI with modulating window/level. Diffusion b0 means the image without motion probing gradient (MPG) and Diffusion b1000 means the image after giving MPG with b1000. The comparison using numerical value of signal intensity of each tumor is not favorable because signal intensity of b0, b1000 and b2000 are obtained by minute induced current and tuned by multiply with more than thousands indicating the error can be large (9). Then, the numerical values of signal intensity are inappropriate. ADC (apparent diffusion coefficient) which implies the slope of the curve, is more reliable for evaluating diffusion repression of water molecule. Calculation of the ADC requires 2 or more acquisitions with different diffusion weightings (10). Namely, ADC of each tissue equals to the slope of the curve using the acquired signal intensity values of b0 and b1000 or b2000 (ADC = - In(Sb/Sb0) / b)(1). An ADC map is drawn using the slope data of each pixel (11).
【Summary】
We presented a seventy five-year-old female suffering from painful swelling at left lower abdomen. Abdomen MRI and CT showed incarcerated inguinal hernia containing greater omentum, urachal mass and uterine lesion. DWIMRI sowed high signal intensity of urachal mass and uterine lesion whose ADC values are 0.51 and 0.37, respectively. Both lesions were thought to indicate abscess rather than tumor (carcinoma). It is borne in mind that ADC values of malignant tumor (carcinoma or sarcoma) are around 1.0 and very rare below 0.7, while ADC values of abscess can lower to around 0.2, although they vary due to the different stage of abscess concentration. In general, ADC values are affected by interruption of vessels, tumor cellularity and abscess: fresh infarction lowers to 0.2, malignant lymphoma to 0.5, pituitary adenoma to 0.5, meningioma to 0.7.
【References】
1.Momeni F, et al. Differentiating Between Low- and High-grade Glioma Tumors Measuring Apparent Diffusion Coefficient Values in Various Regions of the Brain. Oman Med J. 2021;36:e251
2.Maeda M, et al. Apparent diffusion coefficient in malignant lymphoma and carcinoma involving cavernous sinus evaluated by line scan diffusion-weighted imaging. J Magn Reson Imaging 2006;24:543-548
3.Mohamed FF, et al. Diagnostic value of apparent diffusion coefficient (ADC) in assessment of pituitary macroadenoma consistency. The Egyptian Journal of Radiology and Nuclear Medicine. 2013; 44:617-62
4.Liu L, et al. Comparison of ADC values of intracranial hemangiopericytomas and angiomatous and anaplastic meningiomas. Journal of Neuroradiology. 2014;41;188-194
5.Kilickesmez O, et al. Diffusion-Weighted Imaging Features of Urachal Abscess. Istanbul Training and Research Hospital. 2008 DOI:10.15659/yeditepemj.15.10.250
6.Moharamzad Y, et al., Diagnostic performance of apparent diffusion coefficient (ADC) for differentiating endometrial carcinoma from benign lesions: a systematic review and meta-analysis. Abdominal Radiology 2021; 46: 1115–1128
7.Osman NM, et al. The value of the added diffusion-weighted images to multiparametric MRI in the early diagnosis of uterine cervix cancers and nodal assessment. Egyptian Journal of Radiology and Nuclear Medicine. 2021Published: 02 February 2021
8.Parada Villavicencio C, et al. Imaging of the Urachus: Anomalies, Complications, and Mimics. Radiographics : a review publication of the Radiological Society of North America, Inc. 36 (7): 2049-2063.
9.Fujimura M, et al. Apparent diffusion coefficient value for estimating clinicohistological factors in bladder cancer including infiltration style and lymphatic invasion. Springerplus. 2016; 5(1): 848.
10.Kita M. Personal communication in Fuchu Hospital
11.Aoki S et al. Diffusion MRI 3rd edition. Syujunsha 2013 (Japanese)
2021.12.3