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Background
Ovarian malignancies are seventh leading cause of female deaths from cancer and ultrasound is the primary investigative modality. The American College of Radiology (ACR), has recently proposed O-RADS (Ovarian-adnexal Reporting and Data System) ultrasound algorithm, which is aimed at standardization of ultrasound evaluation and interpretation, for accurate assignment of malignancy risk, along with, recommended management for each of the six (0 to 5) categories.The ACR-ORADS is an amalgamation of the North American pattern approach and the algorithmic European approach which is based on IOTA ( International Ovarian Tumor Analysis) strategies. The objective of this presentation is to navigate the reader in a step by step tour of the ORADS ultrasound categories as the category moves from 1 to 5, with a simplified approach.

Educational Goals / Teaching Points
The suggested teaching principle works on progressively moving to a higher category of O-RADS as the gray scale ultrasound and color score (CS) features of the adnexal mass gradually become more complex.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
An incompletely evaluated tumor, on ultrasound is classified category 0. A normal ovarian follicle or corpus luteum cyst, up to 3 cm size are both categorized as O-RADS 1, no follow up is required as there is no malignancy risk in ORADS1. The next category is a simple unilocular cyst without solid contents or septa, up to 10 cm size and is assigned is O-RADS 2 category. The ORADS 2 category also includes 6 classical benign lesions: hemorrhagic cyst, dermoid cyst, endometrioma, paraovarian cyst, peritoneal inclusion cyst and hydrosalpinx, but the upper limit for size is 5 cm, except for a retracting clot in a hemorrhagic cyst, which can be up to 10 cm size. The risk of malignancy in ORADS 2 is 0 - 1% and recommended management is ultrasound surveillance, at 6 - 12 weeks. As the tumor from unilocular becomes multilocular with size up to 10 cm and CS 3, the category moves to 3. Category 3 also includes the 6 classical benign lesions of category 2 when the lesions larger than 5 cm size or solid tumors with smooth margins, with CS 1 - 3, are assigned O-RADS 3. The risk of malignancy in ORADS 3 category is 1 - 10% and recommended management is MRI evaluation followed by gynecology consultation. Multilocular tumors larger than 10 cm, cystic tumors with up to 3 papillae and solid tumors with smooth margins with a color score 2 - 3, are ORADS 4 category. The risk of malignancy in ORADS 4 category is 10-50% and should be managed by a gynecologic oncologist. Tumors associated with ascites, cystic tumors with >4 papillae, solid irregular tumors and tumors with color score 4 are in category 5.The risk of malignancy in ORADS category is >50%. should be managed by a gynecologic oncologist.

Conclusion
The step by step approach based on gray scale features such as unilocular cyst, multilocular cyst, size of lesion, internal septae, solid nodules / contents , papillae, inner and outer margins of cystic / solid tumor, coupled with the vascularity score, can all effectively assist beginners unravel the complex learning path.