RESUMO
Recent innovations in neuroimaging technology have provided opportunities for researchers to investigate connectivity in the human brain by examining the anatomical circuitry as well as functional relationships between brain regions. Existing statistical approaches for connectivity generally examine resting-state or task-related functional connectivity (FC) between brain regions or separately examine structural linkages. As a means to determine brain networks, we present a unified Bayesian framework for analyzing FC utilizing the knowledge of associated structural connections, which extends an approach by Patel et al. (2006a) that considers only functional data. We introduce an FC measure that rests upon assessments of functional coherence between regional brain activity identified from functional magnetic resonance imaging (fMRI) data. Our structural connectivity (SC) information is drawn from diffusion tensor imaging (DTI) data, which is used to quantify probabilities of SC between brain regions. We formulate a prior distribution for FC that depends upon the probability of SC between brain regions, with this dependence adhering to structural-functional links revealed by our fMRI and DTI data. We further characterize the functional hierarchy of functionally connected brain regions by defining an ascendancy measure that compares the marginal probabilities of elevated activity between regions. In addition, we describe topological properties of the network, which is composed of connected region pairs, by performing graph theoretic analyses. We demonstrate the use of our Bayesian model using fMRI and DTI data from a study of auditory processing. We further illustrate the advantages of our method by comparisons to methods that only incorporate functional information.
RESUMO
BACKGROUND: Silent corticotroph adenomas (SCAs) are clinically nonfunctioning pituitary adenomas (NFPAs) with positive staining for corticotropin (ACTH) by immunohistochemistry. Whether SCAs behave more aggressively than NFPAs without ACTH immunoreactivity (ACTH negative) remains controversial. OBJECTIVE: To compare characteristics and outcomes of SCAs with ACTH-negative NFPAs and to identify predictors of aggressive outcome. Primary composite endpoint included the first of any of the following events: progression, recurrence, or death. METHODS: We reviewed all cases of SCAs and all ACTH-negative macroadenomas operated on between April 1995 and December 2007 by 1 neurosurgeon. RESULTS: Our retrospective cohorts included 33 SCAs followed for 42.5 months (median) (range, 6.7-179.0 months) and 126 ACTH-negative patients followed for 42 months (range, 6-142 months). SCA were younger (mean ± SD; 49.6 ± 14.1) than ACTH-negative patients (55.6 ± 12.8, P = .02). Tumor diameter was similar (2.8 ± 1.0 cm); cavernous sinus invasion was present in 45.5% of SCAs and 30.2% of ACTH-negative NFPAs (P = .09). Postoperative tumor residual was detected in 53.1% of SCAs and 49.6% of ACTH-negative patients. Radiation was administered in 40.6% of SCAs at 16 months (range, 3-149 months) and 33.3% of ACTH-negative patients at 13 months (range, 3-94) postoperatively. Progression of residual tumor occurred in 24.2% of SCAs and 11.1% of ACTH-negative patients (P = .08); recurrence was similar (6.0% SCAs vs 5.5% ACTH-negative patients). Cumulative event-free survival rates were not significantly different between the 2 groups (P = .3). Age, sex, tumor size, cavernous sinus invasion, or SCA subtypes were not associated with outcome. CONCLUSION: SCA patients were younger, but exhibited similar postoperative tumor regrowth rates as ACTH-negative macroadenomas while using a similar adjuvant radiation protocol. Long-term follow-up is warranted because predictors of regrowth are currently lacking.
