OBJECT High-resolution PET (hrPET) performed using a high-resolution research tomograph is reported as having a resolution of 2 mm and could be used to detect corticotroph adenomas through uptake of 18F-fluorodeoxyglucose (18F-FDG). To determine the sensitivity of this imaging modality, the authors compared 18F-FDG hrPET and MRI detection of pituitary adenomas in Cushing disease (CD). METHODS Consecutive patients with CD who underwent preoperative 18F-FDG hrPET and MRI (spin echo [SE] and spoiled gradient recalled [SPGR] sequences) were prospectively analyzed. Standardized uptake values (SUVs) were calculated from hrPET and were compared with MRI findings. Imaging findings were correlated to operative and histological findings. RESULTS Ten patients (7 females and 3 males) were included (mean age 30.8 ± 19.3 years; range 11–59 years). MRI revealed a pituitary adenoma in 4 patients (40% of patients) on SE and 7 patients (70%) on SPGR sequences. 18F-FDG hrPET demonstrated increased 18F-FDG uptake consistent with an adenoma in 4 patients (40%; adenoma size range 3–14 mm). Maximum SUV was significantly higher for 18F-FDG hrPET–positive tumors (difference = 5.1, 95% CI 2.1–8.1; p = 0.004) than for 18F-FDG hrPET–negative tumors. 18F-FDG hrPET positivity was not associated with tumor volume (p = 0.2) or dural invasion (p = 0.5). Midnight and morning ACTH levels were associated with 18F-FDG hrPET positivity (p = 0.01 and 0.04, respectively) and correlated with the maximum SUV (R = 0.9; p = 0.001) and average SUV (R = 0.8; p = 0.01). All 18F-FDG hrPET–positive adenomas had a less than a 180% ACTH increase and 18F-FDG hrPET–negative adenomas had a greater than 180% ACTH increase after CRH stimulation (p = 0.03). Three adenomas were detected on SPGR MRI sequences that were not detected by 18F-FDG hrPET imaging. Two adenomas not detected on SE (but no adenomas not detected on SPGR) were detected on 18F-FDG hrPET. CONCLUSIONS While 18F-FDG hrPET imaging can detect small functioning corticotroph adenomas and is more sensitive than SE MRI, SPGR MRI is more sensitive than 18F-FDG hrPET and SE MRI in the detection of CD-associated pituitary adenomas. Response to CRH stimulation can predict 18F-FDG hrPET–positive adenomas in CD.

BACKGROUND AND PURPOSE Intramedullary spinal cord neoplasms (ISCN) in children provide diagnostic, treatment and management dilemmas. Resection results in the best chance for disease control, but the greatest risk of neurologic deficit. We hypothesize that diffusion tensor imaging (DTI) and diffusion tensor-fiber tracking (DT-FT) can help characterize margins of pediatric ISCN to aid in surgical planning. METHODS This HIPAA compliant retrospective study was performed after Institutional Review Board approval. Patients with ISCN from a single tertiary care pediatric institution were identified, and patients with preoperative DTI were evaluated. RESULTS Ten patients (8 males, 2 females) with ISCN with preoperative DTI were identified. The mean age was 11.1 ± 6.2 years (range 2 – 18 years). Eight tumors demonstrated DTI and DT-FT evidence of splayed cord tracts, and two demonstrated evidence of infiltration of cord tracts. The eight patients with splayed tracts underwent resection, with seven achieving gross-total resection and one subtotal resection. The two patients with infiltration of white matter tracts underwent biopsy of their lesion. DISCUSSION DTI of pediatric ISCN can aid in defining the margins of the tumor and relationship to the intrinsic white matter structures of the spinal cord. Splaying and displacement of fiber tracts appears to predict a discrete margin to the tumor and resectability, while infiltration of the white matter tracts suggests biopsy may be more advisable.

We report a patient with Cushing’s disease (CD) and two pituitary adenomas that demonstrated different imaging characteristics and therefore suggest an alternative imaging strategy for these patients. A 42-year-old woman presented with signs and symptoms of CD. Biochemical evaluation confirmed hypercortisolemia and suggested CD. On pituitary MRI with spoiled gradient recalled acquisition in the steady-state and T1-weighted spin echo protocols, a 5 mm hypoenhancing region typical for a pituitary adenoma was identified on the left. However, after surgical resection the patient remained hypercortisolemic and pathology revealed a nonfunctional adenoma. At early repeat surgical exploration a 10 mm adenoma was found in the right side of the gland. Postoperatively the patient became hypocortisolemic and pathology demonstrated an adrenocorticotropic hormone (ACTH)-staining adenoma. On review of the initial MRI this tumor corresponded to a region of contrast retention best visualized on delayed fluid attenuated inversion recovery (FLAIR) imaging. While the incidentaloma in this case demonstrated classical imaging characteristics of a pituitary adenoma the larger ACTH-secreting tumor was best appreciated by contrast retention. This suggests a role for delayed postcontrast FLAIR imaging in the preoperative evaluation of CD. ACTH-secreting tumors causing CD cause significant morbidity. Due to their small size, a pituitary adenoma is frequently not identified on imaging despite endocrinologic testing suggesting CD. Regardless of improvements in MRI, many tumors are only identified at surgical exploration.

Although schwannoma and neurofibroma tumors are generally reported as distinct pathologic diagnoses, sporadic schwannoma/neurofibroma hybrid nerve sheath tumors have been reported in the general population with components of both entities. We report the clinicopathological features of these hybrid nerve sheath tumors in patients with neurofibromatosis type 2 (NF2). A retrospective review of nerve sheath tumor surgical specimens from patients with NF2 enrolled at the National Institutes of Health was performed. Those specimens reported to have schwannoma-like and neurofibromalike features were selected for further characterization by morphology, immunohistochemical panel (CD34, S100, neurofilament triplet protein (immunostain) (NFTP), epithelial membrane antigen (EMA)), and confirmation as hybrid tumors. Of 43 total NF2 patients undergoing resection of nerve sheath tumors, 11 specimens from 11 (26%) patients were found to be benign nerve sheath tumors exhibiting hybrid features of both neurofibroma and schwannoma. Immunohistochemical studies showed the schwannoma component to be S100+, CD 34- while the neurofibroma component was CD34+, variable S100+. Our experience emphasizes the importance of including this distinct tumor subtype, the schwannoma/neurofibroma hybrid tumor, in the differential diagnosis of nerve sheath tumors in NF2 patients and suggests that the relationship between neurofibroma and schwannoma tumors is closer than previously suspected..