Pretreatment Normal WM Magnetization Transfer Ratio Predicts Risk of Radiation Necrosis in Patients with Medulloblastoma.

BACKGROUND AND PURPOSE: Radiation necrosis, for which abnormal WM enhancement is a hallmark, is an uncommon complication of craniospinal irradiation in children with medulloblastoma. The magnetization transfer ratio measures macromolecular content, dominated by myelin in the WM. We investigated whether the pretreatment supratentorial (nonsurgical) WM magnetization transfer ratio could predict patients at risk for radiation necrosis after radiation therapy for medulloblastoma. MATERIALS AND METHODS: Ninety-five eligible patients with medulloblastoma (41% female; mean age, 11.0 [SD, 5.4] years) had baseline balanced steady-state free precession MR imaging before proton or photon radiation therapy. Associations among baseline supratentorial magnetization transfer ratio, radiation necrosis (spontaneously resolving/improving parenchymal enhancement within the radiation field)3, age, and the presence of visible brain metastases were explored by logistic regression and parametric/nonparametric techniques as appropriate. RESULTS: Twenty-three of 95 (24.2%) children (44% female; mean age, 10.7 [SD, 6.7] years) developed radiation necrosis after radiation therapy (19 infratentorial, 1 supratentorial, 3 both). The mean pretreatment supratentorial WM magnetization transfer ratio was significantly lower in these children (43.18 versus 43.50, P = .03). There was no association between the supratentorial WM magnetization transfer ratio and age, sex, risk/treatment stratum, or the presence of visible brain metastases. CONCLUSIONS: A lower baseline supratentorial WM magnetization transfer ratio may indicate underlying structural WM susceptibility to radiation necrosis and may identify children at risk for developing radiation necrosis after craniospinal irradiation for medulloblastoma.

Utility of Pre-Hematopoietic Cell Transplantation Sinus CT Screening in Children and Adolescents.

BACKGROUND AND PURPOSE: The clinical benefit of pre-hematopoietic cell transplantation sinus CT screening remains uncertain, while the risks of CT radiation and anesthesia are increasingly evident. We sought to re-assess the impact of screening sinus CT on pretransplantation patient management and prediction of posttransplantation invasive fungal rhinosinusitis. MATERIALS AND METHODS: Pretransplantation noncontrast screening sinus CTs for 100 consecutive patients (mean age, 11.9 ± 5.5 years) were graded for mucosal thickening (Lund-Mackay score) and for signs of noninvasive or invasive fungal rhinosinusitis (sinus calcification, hyperattenuation, bone destruction, extrasinus inflammation, and nasal mucosal ulceration). Posttransplantation sinus CTs performed for sinus-related symptoms were similarly graded. Associations of Lund-Mackay scores, clinical assessments, changes in pretransplantation clinical management (additional antibiotic or fungal therapy, sinonasal surgery, delayed transplantation), and subsequent development of sinus-related symptoms or invasive fungal rhinosinusitis were tested (exact Wilcoxon rank sums, Fisher exact test, significance P < .05). RESULTS: Mean pretransplantation screening Lund-Mackay scores (n = 100) were greater in patients with clinical symptoms (8.07 ± 6.00 versus 2.48 ± 3.51, P < .001) but were not associated with pretransplantation management changes and did not predict posttransplantation sinus symptoms (n = 21, P = .47) or invasive fungal rhinosinusitis symptoms (n = 2, P = .59). CONCLUSIONS: Pre-hematopoietic cell transplantation sinus CT does not meaningfully contribute to pretransplantation patient management or prediction of posttransplantation sinus disease, including invasive fungal rhinosinusitis, in children. The risks associated with CT radiation and possible anesthesia are not warranted in this setting.

Relative ADC and Location Differ between Posterior Fossa Pilocytic Astrocytomas with and without Gangliocytic Differentiation.

BACKGROUND AND PURPOSE: Pilocytic astrocytomas, the most common posterior fossa tumors in children, are characterized by KIAA1549-BRAF fusions and shows excellent 5-year survival rates. Pilocytic astrocytoma with gangliocytic differentiation, a recently defined pilocytic astrocytoma variant that includes glial and neuronal elements similar to a ganglioglioma, may be distinguished from a classic ganglioglioma by molecular, radiologic, and histopathologic features. This study investigated whether imaging could distinguish posterior fossa pilocytic astrocytoma with and without gangliocytic differentiation. MATERIALS AND METHODS: Preoperative MRIs (± CTs) of 41 children (age range, 7 months to 15 years; mean age, 7.3 ± 3.7 years; 58.5% male) with pilocytic astrocytoma with gangliocytic differentiation (n = 7) or pilocytic astrocytoma (n = 34) were evaluated; differences in tumor location, morphology, and minimum relative ADC between tumor types were compared (Wilcoxon rank sum test, Fisher exact test). Histopathology and BRAF fusion/mutation status were reviewed. Associations of progression-free survival with diagnosis, imaging features, and BRAF status were examined by Cox proportional hazards models. RESULTS: Pilocytic astrocytoma with gangliocytic differentiation appeared similar to pilocytic astrocytoma but had lower minimum relative ADC (mean, 1.01 ± 0.17 compared with 2.01 ± 0.38 for pilocytic astrocytoma; P = .0005) and was more commonly located within midline structures (P = .0034). BRAF status was similar for both groups. Non-total resection (hazard ratio, 52.64; P = .0002), pilocytic astrocytoma with gangliocytic differentiation diagnosis (hazard ratio, 4.66; P = .0104), and midline involvement (hazard ratio, 3.32; P = .0433) were associated with shorter progression-free survival. CONCLUSIONS: Minimum relative ADC and tumor location may be useful adjuncts to histopathology in differentiating pilocytic astrocytoma with gangliocytic differentiation from pilocytic astrocytoma. Shorter progression-free survival in pilocytic astrocytoma with gangliocytic differentiation is likely due to a propensity for involvement of midline structures and poor resectability.

Postoperative intraspinal subdural collections after pediatric posterior fossa tumor resection: incidence, imaging, and clinical features.

BACKGROUND AND PURPOSE: Postoperative intraspinal subdural collections in children after posterior fossa tumor resection may temporarily hinder metastasis detection by MR imaging or CSF analysis, potentially impacting therapy. We investigated the incidence, imaging and clinical features, predisposing factors, and time course of these collections after posterior fossa tumor resection. MATERIALS AND METHODS: Retrospective review of postoperative spine MRI in 243 children (5.5 ± 4.6 years of age) from our clinical data base postresection of posterior fossa tumors from October 1994 to August 2010 yielded 37 (6.0 ± 4.8 years of age) subjects positive for postoperative intraspinal subdural collections. Their extent and signal properties were recorded for postoperative (37/37), preoperative (15/37), and follow-up spine (35/37) MRI. Risk factors were compared with age-matched internal controls (n = 37, 5.9 ± 4.5 years of age). Associations of histology, hydrocephalus and cerebellar tonsillar herniation, and postoperative intracranial subdural collections with postoperative intraspinal subdural collections were assessed by the Fisher exact test or χ(2) test. The association between preoperative tumor volume and postoperative intraspinal subdural collections was assessed by the Wilcoxon rank sum test. RESULTS: The overall incidence of postoperative intraspinal subdural collections was 37/243 (15.2%), greatest ≤7 days postoperatively (36%); 97% were seen 0-41 days postoperatively (12.9 ± 11.0 days). They were T2 hyperintense and isointense to CSF on T1WI, homogeneously enhanced, and resolved on follow-up MR imaging (35/35). None were symptomatic. They were associated with intracranial subdural collections (P = .0011) and preoperative tonsillar herniation (P = .0228). CONCLUSIONS: Postoperative intraspinal subdural collections are infrequent and clinically silent, resolve spontaneously, and have a distinctive appearance. Preoperative tonsillar herniation appears to be a predisposing factor. In this series, repeat MR imaging by 4 weeks documented improvement or resolution of these collections in 88%.

MR imaging evaluation of inferior olivary nuclei: comparison of postoperative subjects with and without posterior fossa syndrome.

BACKGROUND AND PURPOSE: Posterior fossa syndrome is a severe postoperative complication occurring in up to 29% of children undergoing posterior fossa tumor resection; it is most likely caused by bilateral damage to the proximal efferent cerebellar pathways, whose fibers contribute to the Guillain-Mollaret triangle. When the triangle is disrupted, hypertrophic olivary degeneration develops. We hypothesized that MR imaging patterns of inferior olivary nucleus changes reflect patterns of damage to the proximal efferent cerebellar pathways and show association with clinical findings, in particular the presence or absence of posterior fossa syndrome. MATERIALS AND METHODS: We performed blinded, randomized longitudinal MR imaging analyses of the inferior olivary nuclei of 12 children with and 12 without posterior fossa syndrome after surgery for midline intraventricular tumor in the posterior fossa. The Fisher exact test was performed to investigate the association between posterior fossa syndrome and hypertrophic olivary degeneration on MR imaging. The sensitivity and specificity of MR imaging findings of bilateral hypertrophic olivary degeneration for posterior fossa syndrome were measured. RESULTS: Of the 12 patients with posterior fossa syndrome, 9 had bilateral inferior olivary nucleus abnormalities. The 12 patients without posterior fossa syndrome had either unilateral or no inferior olivary nucleus abnormalities. The association of posterior fossa syndrome and hypertrophic olivary degeneration was statistically significant (P < .0001). CONCLUSIONS: Hypertrophic olivary degeneration may be a surrogate imaging indicator for damage to the contralateral proximal efferent cerebellar pathway. In the appropriate clinical setting, bilateral hypertrophic olivary degeneration may be a sensitive and specific indicator of posterior fossa syndrome.

Imaging of acute invasive fungal rhinosinusitis in a patient with gorlin syndrome and acute lymphocytic leukemia.

Gorlin Syndrome (GS), also known as nevoid basal cell carcinoma syndrome, is a rare autosomal dominant condition characterized by developmental abnormalities and predisposition to certain neoplasms. Acute invasive fungal rhinosinusitis (AIFRS) is an uncommon clinical entity characterized by high morbidity and mortality. In immunocompromised patients, computed tomography plays a critical role in screening for suspected AIFRS. However, due to the association between exposure to ionizing radiation and subsequent development of malignancies in patients with GS, patients with GS and suspected AIFRS present a unique and challenging clinical scenario. We present a case of a pediatric patient with GS and acute lymphocytic leukemia (ALL) diagnosed with AIFRS; to the best of our knowledge, it is the only case described in the literature.

Imaging changes in very young children with brain tumors treated with proton therapy and chemotherapy.

SUMMARY: PT promises to reduce side effects in children with brain tumors by sparing normal tissue compared with 3D conformal or intensity-modulated radiation therapy. Information is lacking about the combined effects of PT and chemotherapy in young children. We describe imaging changes in 8 very young children with localized brain tumors who received PT after chemotherapy. Mostly transient signal abnormalities and enhancement in brain parenchyma were observed by serial MR imaging, which were consistent with radiation-induced effects on normal-appearing tissue. Correlation with PT planning data revealed that the areas of imaging abnormality were located within or adjacent to the volume that received the highest radiation dose. Radiologists should be aware of these findings in children who receive PT after chemotherapy. In this report, we describe the time course of these PT-related imaging findings and correlate them with treatment and clinical outcomes.

Time-to-echo optimization for spin echo magnetic resonance imaging of liver metastasis using superparamagnetic iron oxide particles.

Superparamagnetic iron oxide (SPIO) particles are used as a contrast agent in liver magnetic resonance imaging (MRI). SPIO particles exert their greatest influence on T2-weighted MR signal intensity. The time-to-echo (TE) value that provides optimal contrast has not been systematically studied over the range of clinically relevant field strengths. The purpose of this study was to quantitatively evaluate the TE dependence of the post-SPIO tumor to liver contrast-to-noise ratio (CNR). The hypothesis was that there is a TE that provides an optimal CNR. Subjects having probable metastatic hepatic lesions secondary to colorectal carcinoma were studied. Pre- and post-SPIO images were acquired at TE-effective (TE(eff)) equal to 46, 76, and 106 msec by using a turbo spin echo pulse sequence at 0.2 T and 1.5 T. The CNR for all lesions greater than 1 cm in diameter was determined in pre- and post-SPIO images. A paired statistical design was used to identify TE-related CNR dependencies. The primary findings were as follows. (1) CNR differences attributable to TE(eff) variation over the range of 46-106 msec were less than 34%. For 0.2 T, TE(eff) = 46 msec yielded a statistically significantly greater CNR than did TE(eff) = 76 or 106 msec. The same was true at the higher field strength, but differences were not significant. (2) Signal-to-noise measures suggested that SPIO reduced the lesion signal. (3) Post-SPIO CNR was significantly greater at 1.5 T than at 0.2 T. The observations indicate that over the field strength range of 0.2-1.5 T, CNR differences attributable to the TE(eff) variation, while being statistically significant in some cases, are small relative to those resulting from the SPIO administration.