MRI of the brain is often performed for patients with primary headaches, which account for about 90% of all headaches. An incidental finding (IF) or normal anatomical variant is frequently revealed and may cause concern for the patient and family. Before MRI is done for primary headaches, it is useful to advise patients that the chance of finding an abnormality that is causing the headache is very small, but that an incidental finding or normal anatomic finding is common. This may decrease potential anxiety for the patient and save you time.
Prevalence of Incidental Findings
A number of studies have reported IFs in normal volunteers, with the prevalence of clinically significant neuropathologies occurring in an estimated 2%-8% of the general population.[1]
In a meta-analysis of 16 studies of 19,559 people aged 0-97 years with no neurologic symptoms who underwent MRI of the brain with or without contrast for research purposes or occupational, clinical, or commercial screening, the overall prevalence of IF was 2.7% (4.3% in studies where participants underwent at least one high-resolution MRI sequence vs 1.7% in studies using only low-resolution sequences).[2] White-matter hyperintensities, silent brain infarcts, brain microbleeds, and anatomical variants were not included. The following IFs were found: neoplasia, 0.70% prevalence (meningioma, 0.29%; pituitary adenoma, 0.15%; low-grade glioma, 0.05%; acoustic neuroma, 0.03%; lipoma, 0.04%; epidermoid, 0.03%); structural vascular abnormality, 0.56% (aneurysm, 0.35%; cavernous malformation, 0.16%; arteriovenous malformation, 0.05%); cyst, 0.54% (arachnoid cyst, 0.50%; colloid cyst, 0.04%); Chiari I malformation, 0.24%; hydrocephalus, 0.10%; inflammatory lesion, 0.09% (definite demyelination, 0.06%; possible demyelination, 0.03%); and extra-axial collection, 0.04%.
Figure 1. Arteriovenous malformation of the brain. An axial T2-weighted MRI shows numerous flow voids. Note the mass effect on the lateral ventricle despite the lack of a mass or hemorrhage. Image from Dr Evans.
Figure 2. Axial T2-weighted MRI through the body of the lateral ventricles, showing superior extension of a right middle cranial fossa lesion. The lesion is homogeneous, with no perceptible wall, no internal complexity, and CSF signal intensity. There is associated remodeling of the adjacent calvarium and brain displacement. These features are typical of an arachnoid cyst. Image from Dr Evans
In a study of 203 healthy volunteers aged 18-35 years who underwent MRI, 30.5% had variations of normal findings.[3] The three most common were pineal gland cyst, widened bifrontal subarachnoid space, and Rathke cleft cyst. IFs occurred in 9.4% of the volunteers, with the most common being occasional/not important white-matter lesions and Chiari I malformations. Among 180 participants who had their upper head and neck region evaluated, 3.3% had findings that were variations of the norm (most commonly hypoplastic frontal or maxillary sinus) and 36.7% had abnormal findings (most commonly sinonasal retention cyst or polyp, isolated mucosal swelling, and pharyngeal or parotid lymphadenopathy).
In a retrospective study of MRI scans of 2536 healthy young men (aged 17-35 years), normal anatomical variants were present in 18.14% of participants: cavum vergae, 4.77%; pineal gland cysts, 3.43%; asymmetry of the lateral ventricles, 2.68%; occasional white-matter lesions, 2.60%; enlarged perivascular spaces, 2.56%; large basal cisterns, 1.74%; empty sella, 0.35%; and ossification of the cerebral falx, 0.32%.[4]
In a general population study of 2000 persons aged 45-97 years living in Rotterdam, The Netherlands, the following IFs were recorded: asymptomatic brain infarct, 7.2% (lacunar, 5.6%; cortical, 2.0%); aneurysm, 1.8%; benign primary tumor, 1.6% (meningioma, 0.9%; pituitary tumor, 0.3%; vestibular schwannoma, 0.2%; lipoma, 0.1%); arachnoid cyst, 1.1%; Chiari I malformation, 0.9%; major-vessel stenosis, 0.5%; cavernous angioma, 0.4%; malignant primary tumor, < 0.1%; metastases, < 0.1%; and subdural hematoma, < 0.1%.[5] Asymptomatic brain infarcts were found in 4% of participants aged 45-59 years, 6.8% of those aged 60-74 years, and 18.3% of those aged 75-97 years. The median volume of white-matter lesions was 1.8 mL in those aged 45-90 years, 3.1 mL in those aged 60-74 years, and 7.74 mL in those aged 75-97 years. All but three of the 35 aneurysms detected were smaller than 7 mm in diameter and all but two were located in the anterior circulation.
Figure 3. Large right frontal and left occipital cavernous angiomas on a T1-weighted axial MRI. These two heterogeneous masses have a reticulated core of high and low signal intensities surrounded by a hypointense rim of hemosiderin. Image from Dr Evans.
Numerous incidental findings and anatomical variants have been observed in adults and children, ranging from aneurysms to white-matter abnormalities. Two recent review articles provide information on 21 types in adults[6] and 11 types in children.[7]
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Cite this: Headache MRI: What to Do With Incidental Findings - Medscape - Aug 28, 2018.
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