The role of "penumbra sign" and diffusion-weighted imaging in adnexal masses: do they provide a clue in differentiating tubo-ovarian abscess from ovarian malignancy?

Abstract

Purpose: To evaluate the role of "penumbra sign", diffusion-weighted imaging (DWI), and the apparent diffusion coefficient (ADC) value in differentiating tubo-ovarian abscess (TOA) from ovarian malignancy.

Material and methods: Thirty-six patients with 50 adnexal masses (tubo-ovarian abscess, n = 24; ovarian malignancy, n = 26), who underwent magnetic resonance imaging (MRI) with DWI, were retrospectively evaluated. "Penumbra sign" (hyperintense rim on T1W images), diffusion restriction, and mean apparent diffusion coefficient (ADC) values from cystic (c-ADC) and solid (s-ADC) components were evaluated for all the masses.

Results: "Penumbra sign" on T1W images was significantly more common in the TOA group (n = 21, 87.5%) than in the ovarian malignancy group (n = 2, 7.7%) (p < 0.001). Similarly, diffusion restriction in the cystic component was more frequent in the TOA group (n = 24, 100% vs. n = 2, 10.5%; p < 0.001). In contrast, diffusion restriction in the solid component was more common in the ovarian malignancy group (n = 5, 20.8% vs. n = 26, 100%; p < 0.001). The mean c-ADC value was significantly lower in TOAs (p < 0.001). A c-ADC value of 1.31 × 10-3 mm2/s may be an optimal cut-off in distinguishing TOAs from ovarian malignancies. Conversely, the mean s-ADC value was significantly lower in the ovarian malignancy group (p < 0.001). An s-ADC value of 0.869 × 10-3 mm2/s may be an optimal cut-off in differentiating ovarian malignancies from TOAs (p < 0.001). ROC curve analysis showed that c-ADC values had a higher diagnostic accuracy than s-ADC values.

Conclusions: "Penumbra sign" on T1W images, diffusion characteristics, and ADC values provide important clues in addition to conventional MR imaging features in differentiating TOA from ovarian malignancy.

Keywords: apparent diffusion coefficient (ADC); conventional MRI; diffusion-weighted imaging (DWI); ovarian malignancy; penumbra sign; tubo-ovarian abscess (TOA).

Conflict of interest statement

The authors report no conflict of interest.

Copyright © Polish Medical Society of Radiology 2021.

Figures

Figure 1

Penumbra sign on T1-weighted images. A) Right tubo-ovarian abscess shows a complex adnexal mass with hyperintense rim along the inner walls of cavities (white arrows) – termed as “penumbra sign”. B) The cavity of tubo-ovarian abscess in another patient also shows hyperintense rim (white arrows)

Figure 2

Left-sided tubo-ovarian abscess in a 21-year-old female. A) Axial T2W image shows a complex solid-cystic right adnexal mass with a few incomplete septae (yellow arrows). B) Axial T1W image shows “penumbra sign” (white arrows B). C) CE-T1W image depicts enhancing thick irregular septae, solid peripheral component, and irregular enhancement in the surrounding. D) DWI image showing marked diffusion restriction in the abscess cavity (red asterisks) with (E) low ADC values (minimum ADC of 0.560 × 10-3 mm2/s); F) solid component appears hypointense on DWI with higher ADC values (minimum value of 1.305 × 10-3 mm2/s)

Figure 3

Right tubo-ovarian abscess (tubercular) in a 32-year-old female. A) Axial T2W image shows a complex solid cystic right adnexal mass of intermediate signal intensity. B) Axial T1W image at a slightly lower level shows “penumbra sign” around the abscess cavity (white arrows). C) Post-contrast T1WI image showing enhancing solid components. D) DWI image shows marked diffusion restriction in cystic areas (red arrows) with a minimum ADC value of 0.352 × 10-3 mm2/s (E), whereas solid tissue (F) does not show diffusion restriction with an ADC value of 1.153 × 10-3 mm2/s

Figure 4

Bilateral ovarian serous cystadenocarcinoma. Axial T2W (A) and T1W (B) images show complex T2 intermediate and T1 hypointense multilocular solid-cystic masses in bilateral adnexae with multiple papillary projections (red arrows A); no “penumbra sign” is noted; contrast-enhanced T1W image (C) shows enhancing solid components and septae. Axial DW image (D) reveals marked diffusion restriction in the solid areas (white arrows) with (E) low ADC values (minimum ADC value of 0.565 × 10-3 mm2/s); F) cystic component showing facilitated diffusion with higher ADC values (minimum value of 2.495 × 10-3 mm2/s)

Figure 5

Juvenile granulosa cell tumour of the left ovary. Axial T2W (A) and T1W Non-FS (B) images show a well-defined T2 intermediate and T1 hypointense solid-cystic left ovarian mass; few T1 hyperintense cystic areas are noted (yellow arrows B), indicating haemorrhage; T1W image (C) at a lower section showing a T1 hyperintense rim around the cyst (white arrow C); post-contrast T1WI image (D) shows enhancing solid component; axial DWI image (E) depicts high signal in the solid as well as cystic (red arrows E and F) areas with low signal on corresponding ADC map (F), suggesting diffusion restriction; ADC value measured in the solid area is 0.837 × 10-3 mm2/s

Figure 6

ROC curves analysis show greater area under the curve (AUC) for c-ADC values (A) than that of s-ADC values (B), indicating that c-ADC has higher diagnostic accuracy than s-ADC in differentiating a tubo-ovarian mass from an ovarian malignancy