Technical Note Dynamic Intraoperative MRI in Transsphenoidal Resection of Pituitary Macroadenomas: A Quantitative Analysis Alessandro Boellis, MD, 1 * Maria Camilla Rossi Espagnet, MD, 1 Andrea Romano, MD, 2 Giuseppe Trill  o, MD, 3 Antonino Raco, MD, 3 Marta Moraschi, MSc, 4 and Alessandro Bozzao, MD 1 Purpose: To compare intraoperative dynamic contrast- enhanced (dCE) sequences with conventional CE (cCE) in the evaluation of the surgical bed after transsphenoidal removal of pituitary macroadenomas. Materials and Methods: Twenty-one patients with mac- roadenoma were selected. They all underwent intraopera- tive magnetic resonance imaging (iMRI) (1.5T) acquisitions during transsphenoidal resection of the tumor. For each patient, dCE and cCE images were acquired in the operating room after tumor removal. The mean values of surgical cavities volumes were measured and statistically compared through Student’s t-test analy- sis. Informed consent to iMRI was obtained from the patients as a part of the surgical procedure. Institutional Review Board (IRB) approval was obtained. Results: No patient showed recurrence within at least 1 year of follow-up. Two patients showed residual tumor in the iMRI. Intraoperative analysis of the remaining 19 demonstrated that the mean value of the surgical cavities was significantly bigger in dCE than in cCE images (2955 mm 3 vs. 1963 mm 3 , respectively, P ¼ 0.022). Conclusion: This study demonstrated underestimation of surgical cavity by conventional iMRI, simulating resid- ual tumor and potentially leading to unnecessary surgical revision. Key Words: dynamic iMRI; intraoperative MRI; pituitary macroadenoma; transsphenoidal surgery J. Magn. Reson. Imaging 2014;40:668–673. V C 2013 Wiley Periodicals, Inc. TRANSSPHENOIDAL RESECTION of macroadenomas is a safe, validated technique for neoplasm removal in the pituitary region (1). Intraoperative magnetic reso- nance imaging (iMRI) has been proposed for the assessment of surgical procedures, including the transsphenoidal approach. The main advantages of iMRI are the detection of residual tumor and identifi- cation of complications (2–4); 20%–30% of intraopera- tive images indeed showed residual tumor in patients treated with the transsphenoidal approach, although with considerable variability (5%–66%) (5–7). iMRI is also a valuable tool for the surgeon to identify the pre- cise location of the tumor distinguishing normal gland from neoplastic tissue (3). MRI with dynamic contrast injection was proven to be a useful tool in the evaluation of pituitary patholo- gies (8). Enhancement involves the pituitary stalk first, then the normal gland, and finally pituitary adenoma (9). This peculiar temporal sequence makes dynamic contrast-enhanced (dCE) more effective than conven- tional contrast-enhanced (cCE) imaging, especially for identifying normal pituitary displaced by the tumor (8). The acquisition of dCE sequences using iMRI during transsphenoidal surgery has been described in only a few studies (10,11). Some authors (6,10) have suggested that surgical procedures may cause enhancement within the surgical bed, simulating a residual tumor on cCE. Our hypothesis was that dCE sequences could overcome this problem leading to a more realistic evalu- ation of the surgical cavity. This was the purpose of our study and was done by comparing the surgical cavity size in dCE and cCE sequences performed intraopera- tively after resection of pituitary macroadenomas. MATERIALS AND METHODS Images were acquired in Brain Suite (Brain Lab, Heim- stetten, Germany), an operating room dedicated to 1 Neuroradiology NESMOS Department, University of Rome “La Sapi- enza” and Azienda Ospedaliera Sant’Andrea, Rome. 2 Fondazione San Raffaele, Merit project RBNE08E8CZ, Ceglie, Mes- sapica, Italy. 3 Neurosurgery NESMOS Department, University of Rome “La Sapi- enza” and Azienda Ospedaliera Sant’Andrea, Rome. 4 Medical Physics Department, University of Roma “La Sapienza: and Azienda Ospedaliera Sant’Andrea, Rome. *Address reprint requests to: A.B., Neuroradiology NESMOS Depart- ment, University of Rome “La Sapienza” and Azienda Ospedaliera Sant’Andrea, Rome. E-mail: alessandroboellis@gmail.com [Correction added after online publication September 23, 2013: In the first sentence of the first paragraph on the second page of this article, December 2010 has be corrected to December 2009. We apologize for this error.] Received March 20, 2013; Accepted August 19, 2013. DOI 10.1002/jmri.24414 View this article online at wileyonlinelibrary.com. JOURNAL OF MAGNETIC RESONANCE IMAGING 40:668–673 (2014) CME V C 2013 Wiley Periodicals, Inc. 668