Wednesday, June 14, 2017

Incidental findings in MRIs done for primary headaches in adults

Evans RW. Incidental Findings and Normal Anatomical Variants on MRI of the Brain in Adults for Primary Headaches. Headache. 2017 May;57(5):780-791.

When MRI scans of the brain are obtained for evaluation of primary headaches in adults, incidental findings are commonly present. After a review of the prevalence of incidental findings and normal anatomical variants, 21 types are presented.

From the article

About 90% of all headaches are the primary type where MRI scans of the brain will not reveal any pathology responsible for headaches. MRI scans are frequently done for primary headaches for a variety of reasons including the following: secondary pathology; at the patient's or family's request; to reassure the patient, “our stubborn quest for diagnostic certainty;”  faulty cognitive reasoning; the medical decision rule where it is better to impute disease than to risk overlooking it; busy practice conditions where tests are ordered as a shortcut; financial incentives; professional peer pressure where recommendations for routine and esoteric tests are expected as a demonstration of competence; and medicolegal concerns. Incidental findings are common, often revealing benign pathology which may cause concern of the patient. Normal anatomical variants are also common.  Definitions may differ among investigators as some may classify normal anatomical variants as incidental findings while others may not.


Case 1
This is a 32-year-old male with a history of increasingly frequent episodic migraine. MRI of the brain was normal except for a 7 mm pineal cyst. Another MRI of the brain 5 years later for chronic migraine showed no change in the size of the cyst.

Case 2
This is a 27-year-old male, the brother of case 1, with a history of headaches consistent with migraine without aura since childhood. Headaches have increased to twice a week in frequency. Past medical history is negative. Neurological examination is normal. Magnetic resonance imaging (MRI) of the brain shows a left anterior cranial fossa arachnoid cyst measuring 1.2-cm anteroposterior by 1.6-cm transverse by 1.5-cm craniocaudad without significant parenchymal compression. He is placed on a triptan with a good response….

There have been a number or studies which report IF in normal volunteers with the prevalence of clinically significant neuropathologies occurring in 2-8% of the general population.
In a meta-analysis of 16 studies of 19,559 people with a range of 1-97 years without neurological symptoms who underwent MRI of the brain with or without contrast for research purposes or for occupations, 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 versus 1.7% in studies using only low resolution sequences). White matter hyperintensities, silent brain infarcts, brain microbleeds, and anatomical variants were not included. The following IF and prevalences (%) were found: neoplasia, 0.7 (meningioma, 0.29; pituitary adenoma, 0.15; low grade glioma, 0.05, acoustic neuroma, 0.03; lipoma, 0.04; epidermoid, 0.03); structural vascular abnormalites, 0.56 (aneurysm, 0.35; cavernous malformation, 0.16; arteriovenous malformation 0.05); inflammatory lesions, 0.09 (definite demyelination, 0.06; possible demyelination, 0.03); cysts, 0.54 (arachnoid cysts, 0.5; colloid cyst, 0.04), Chiari I malformation, 0.24; hydrocephalus, 0.10; and extra-axial collection, 0.04.

In a study of 206 healthy volunteers ages 9-50 years (mean 25.68 years) on a 3-tesla MRI scanner, 19% had incidental findings.  IF without clinical importance were present in 9% as follows: signal abnormalities, 4%; pineal cysts < 1 cm, 3%; and mega cisterna magna, 1%. IF with clinical importance were present in 10% as follows: intrasellar abnormalities, 6%; pineal cysts >1 cm, 2%; cavernomas, 1%; arteriovenous malformations, 1%; multiple white matter lesions, 1%; Chiari malformation, 1%; subependymal heterotopia, .5%; and multiple sinusoidal polpys, 1%.

In a study of 203 healthy volunteers ages 18-35 years (mean 21.9 years) on a 1.5-tesla MRI scanner, 30.5% had variations of the norm including the 3 most common as follows: pineal gland cyst, 6.1%; widened bifrontal subarachnoid space, 6.1%; and Rathke cleft cyst, 3.9%.[8] IF of the brain were found in 9.4% with occasional/not important white matter lesions, 4.4% and Chiari I malformations, 1%. In 180 participants, the upper head and neck region were evaluated, finding 3.3% with variants of the normal (most common hypoplastic frontal or maxillary sinus) and 36.7% with abnormal findings (most common sinonasal retention cyst or polyp, 10%; isolated mucosal swelling, 6.1%; pharyngeal or parotid lymphadenopathy, 5%; and cystic lesion in the parotid gland, 1%.

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