Incidental Findings on Pediatric MR Images of the Brain

Methods

Results

Abnormalities of all categories of clinical importance were detected in 47 (21%) of the 225 studies reviewed, as shown in Table 1. Of these, 18 (38% of abnormalities or 8% of the total subject population) required either routine (17 cases) or urgent (1 case) clinical referral. No cases were in the immediate referral category. Two subjects presented with more than one finding. One of these subjects had acute sinusitis and a posterior fossa arachnoid cyst, and the other subject had a pineal cyst and sphenoid sinusitis.

The classification of all detected abnormalities is presented in Table 2. Extracranial abnormalities (eg, sinusitis) were found in 12% of subjects and accounted for 55% of all incidental findings. Intracranial abnormalities (eg, focal white matter lesions and other findings not related to sinus disease) were found in 9% of the subjects and accounted for 45% of the incidental findings. The age distribution of the subjects in whom these abnormalities was found is shown in Table 3.

We further analyzed the data according to sex and found that the incidence of neuroradiologic findings in male subjects was approximately twofold compared with that of the female subjects (Table 4; χ²=5.12; P < .05). More than one-third of the male subjects with a detected abnormality required at least routine referral. When we removed the cases of sinusitis that did not require referral from the analysis because of their clinical unimportance, more than one-half of the abnormal findings in both female and male subjects were considered to have required clinical referral (Table 5; χ²=4.5; P < .05).

Discussion

In 1999, Katzman et al (2) retrospectively studied the prevalence of incidental imaging findings in a healthy asymptomatic population. They reported an 18% incidence of findings in their cohort of 1000 research subjects (54.6% male, 45.4% female; mean age, 30.6 years; age range, 3–83 years). Of the findings they detected, 15.1% required no referral; 1.8%, routine referral; 1.1%, urgent referral; and 0.2%, immediate referral. Other clinical studies have addressed the prevalence of the incidental radiologic finding of sinus disease in adult patients presenting with symptoms such as a chronic cough, seizures, head injuries, and various intracranial diseases (3–6). Variations in incidental findings across age have also been observed, including incidental findings of white matter lesions (7), sinus disease (8), and focal white matter abnormalities (9) in symptomatic subjects.

In the present study, we retrospectively explored the frequency and clinical importance of incidental findings on brain MR images in a neurologically healthy pediatric population involved in fMRI research. Our data broadly replicate those of Katzman et al (2) in adults; for example, our 21% overall prevalence of incidental findings is generally consistent with the 18% of findings overall in healthy adults in the report by Katzman et al, with sinusitis in 12% of the adult cohort. In addition, albeit limited, the ventricular asymmetry found in one of two neonatal subjects is also consistent with the incidence of approximately 45% that Shen and Huang reported (10).

Although the age distribution in our sample was not homogeneous and although the overall incidence of clinically important findings in the total population was relatively small, nearly 10% of subjects had findings that were categorized as requiring at least routine referral. In contrast to findings in older adults, small foci of abnormal signal intensity on MR images are always of concern in children, whether the findings are in the deep gray matter or in the white matter. For example, small foci of abnormal signal intensity were strongly associated with neurofibromatosis (NF)-1 in a study by DeBella et al (11) in which 43–93% of children with NF-1 presented with such focal signal intensity abnormalities. Consequently, such findings on MR images have been proposed as a diagnostic criterion for NF-1. Our 2.2% incidence of such findings in healthy children is concordant with expected frequencies, although it is less than the incidence in the study by DeBella et al (11). Nevertheless, such findings should prompt further follow-up and routine referral of the subject to a physician or clinical setting.

We also report differences in the prevalence of total incidental findings related to sex. In addition to the twofold increase in the incidence of abnormalities in male subjects compared with female subjects, the male subjects also had a greater variety of incidental findings. Moreover, when we factored out all of the extracerebral findings (eg, sinus disease), the male subjects had a 17% incidence of intracerebral abnormalities, whereas the female subjects had a 3% incidence of such abnormalities. Previous studies have also shown some differences in the prevalence of certain findings across sex (12, 13), with a higher prevalence of pineal cysts reported in young women (14). Although the importance of these sex-related differences is uncertain, MR imaging researchers must be cognizant of such population-related variations.

The disproportionately limited ethnicity of the cohort, which included subjects of primarily European or Asian descent, may be a potential confounding factor in this study. Its effect is unknown at this time. and future multicenter investigations may help to broaden our understanding of the potential geographic, environmental, and genetic effects of the findings.

Conclusion

The prevalence of incidental MR imaging findings in the healthy pediatric population reported here, as well as the prevalence of unidentified bright objects and ventricular asymmetry in the neonatal subjects, are consistent with the results of previous research studies in adults and in clinical studies of adult and children. In addition to these findings, new findings of strong intersex differences and intracerebral abnormalities are other factors that must be taken into account when population variations are considered in fMRI.

Although the MR imaging findings reported here did not compromise the interpretability or validity of the research studies (subjects with intracranial abnormalities were excluded from analyses), even the limited presence of such findings in a cohort of young participants is a matter of medical concern. The findings suggest that researchers must develop specific procedures for managing the brain MR imaging examination that includes proactive involvement of the neuroradiology community both for the detection of abnormalities and for their appropriate follow-up. Such procedures should be applicable at a broad level, in a cost-effective fashion, and in a consistent and clinically appropriate manner.