"When, in the judgment of the Secretary, expert medical opinion, in addition to that available within the Department, is warranted by the medical complexity or controversy involved ... the Secretary may secure an advisory medical opinion from one or more independent medical experts who are not employees of the Department." 38 U.S.C. § 5109(a) (emphasis added); see also 38 U.S.C. § 7109(a). The determination that an expert medical opinion is warranted is left entirely to the discretion of the Secretary. 38 U.S.C. § 7261(a)(3)(A); see Boutwell v. West, 11 Vet. App. 387, 391 (1998); Stringham v. Brown, 8 Vet. App. 445, 448 (1995).
An examination report "is adequate when it is based upon consideration of the [appellant's] prior medical history and examinations and also describes the disability, if any, in sufficient detail so that the Board's 'evaluation of the claimed disability will be a fully informed one.'" Stefl v. Nicholson, 21 Vet. App. 120, 123 (2007) (quoting Ardison v. Brown, 6 Vet. App. 405, 407–08 (1994)); Green v. Derwinski, 1 Vet. App. 121, 124 (1991). It is a medical examiner's responsibility to provide a well-supported opinion so that the Board may carry out its duty to weigh the evidence of record. See Nieves–Rodriquez v. Peake, 22 Vet. App. 295, 304 (2008) (medical opinion is not entitled to any weight if it contains only data and conclusions); Stefl, 21 Vet. App. at 124 (a VA medical opinion "must support its conclusion with an analysis that the Board can consider and weigh against contrary opinions"). "It is the factually accurate, fully articulated, sound reasoning for the conclusion ... that contributes probative value to a medical opinion." Nieves-Rodriguez, 22 Vet. App. at 304; Stefl, 21 Vet. App. at 124 (holding that a medical examination report must contain not only clear conclusions with supporting data, but also a reasoned medical explanation connecting the two); see also D'Aries v. Peake, 22 Vet. App. 97, 104 (2008) ("Whether a medical opinion is adequate is a finding of fact which this Court reviews under the 'clearly erroneous' standard of review.").