title: The shading sign: is it exclusive of endometriomas?
abstract: OBJECTIVE
  To investigate if the shading sign is an exclusive MRI feature of endometriomas or endometrioid tumors, and to analyze its different patterns.
  
  
  METHODS
  Three hundred and fourty six women with adnexal masses who underwent 1.5/3-T MRI were included in this retrospective, board-approved study. The shading sign was found in 56 patients, but five cases were excluded due to lack of imaging follow-up or histological correlation. The final sample included 51 women. The type of tumor and the pattern of shading were recorded for each case.
  
  
  RESULTS
  Thirty endometriomas and five endometrioid carcinomas were found. The remaining 16 cases corresponded to other benign and malignant tumors. The overall sensitivity, specificity, positive predictive value, and negative predictive value were 73%, 93%, 59%, and 96%, respectively. Restricting the analysis to cystic lesions without solid or fat component, sensitivity, specificity, positive predictive value, and negative predictive value were 73%, 96%, 94%, and 80%. Five shading patterns were identified: layering (15.7%), liquid-liquid level (11.8%), homogenous (45.1%), heterogeneous (11.8%), and focal/multifocal shading within a complex mass (19.6%). No significant correlation was found between these patterns and the type of tumor.
  
  
  CONCLUSIONS
  The shading sign is not exclusive of endometriomas or endometrioid tumors. Homogenous shading was the most prevalent pattern in endometriomas and half of the cases with focal/multifocal shading within a complex mass were endometrioid carcinomas.
authors.affiliation: Department of Radiology, Hospital de S. José, Centro Hospitalar de Lisboa Central, Rua José António Serrano, 1150-199, Lisbon, Portugal. joaolopesdias85@gmail.com.|Faculdade de Ciências Médicas, NOVA Medical School, Lisbon, Portugal. joaolopesdias85@gmail.com.
authors.forename: João Lopes
authors.initials: JL
authors.lastname: Dias
authors.affiliation: Department of Radiology, Centro Hospitalar do Algarve, Rua Leão Penedo, 8000-386, Faro, Portugal.|Department of Biomedical Sciences and Medicine, Regenerative Medicine Program, University of Algarve, Faro, Portugal.
authors.forename: Filipe
authors.initials: F
authors.lastname: Veloso Gomes
authors.affiliation: Department of Radiology, Hospital de St. António dos Capuchos, Centro Hospitalar de Lisboa Central, Alameda de Santo António dos Capuchos, 1169-050, Lisbon, Portugal.
authors.forename: Rita
authors.initials: R
authors.lastname: Lucas
authors.affiliation: Department of Radiology, Instituto Português de Oncologia de Lisboa Francisco Gentil, Rua Professor Lima Basto, 1099-023, Lisbon, Portugal.
authors.forename: Teresa Margarida
authors.initials: TM
authors.lastname: Cunha
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018269:Carcinoma, Endometrioid / Q000473:pathology*; D003937:Diagnosis, Differential; D016889:Endometrial Neoplasms / Q000473:pathology*; D004715:Endometriosis / Q000473:pathology*; D004717:Endometrium / Q000473:pathology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult
keywords: Endometrioid carcinoma; Endometrioma; Gynecology; Imaging; Magnetic resonance imaging