Microsoft Word - PNE223BF.rtf

The Neuro Image Quiz, Answers T.P. Thomas P. Naidich Thomas P. Naidich, MD, Division of Neuroimaging, Children’s Memorial Hospital, 2300 Children’s Plaza, Chicago, IL 60614 (USA) These images demonstrate a well-circumscribed lobu-lated erosion of the anterior parietal bone, situated just posterior to the coronal suture. In this case the zone of transition from obviously normal bone to obviously pathological bone is very narrow. When the zone of transition is narrower than 3-5 mm on all borders, the lesion usually has low aggressivity. It is expanding slowly, so it is much more likely to be benign. Malignant lesions tend to be permeative and to infiltrate the adjacent bone, producing a wide zone of transition. The answer to question 1 is benign. Analysis of the zone of transition is the basic step in radiological diagnosis of calvari-al lesions. There are pitfalls, however. First, a malignant lesion may exhibit a narrow zone of transition on nearly all sides when it develops as malignant degeneration of a previously benign lesion, e.g. sarcomatous degeneration of fibrous dysplasia. Second, a benign inflammatory/infective lesion may permeate widely producing a very wide zone of transition. Thus, infection can be very difficult to differentiate from malignancy. Nonetheless, analysis of the zone of transition usually distinguishes benign from malignant lesions [1]. Within the group of benign lesions, the speed of lesion growth can be assessed by reviewing the degree of sclerosis along the margin of the lesion. Very slowly growing lesions afford time for the calvarium to enclose the lesion in a dense rim or ‘rind’ of sclerosis. Dermoid and epidermoid tumors commonly exhibit such a rind. So do some hemangiomas. Benign but more aggressive lesions expand more rapidly and afford less time for deposition of bone, creating a narrow (pencil-thin) rim of bone. More active, but still benign, lesions exhibit a sharp zone of transition with no sclerotic rim at all. Eo-sinophilic granuloma is an aggressive benign lesion and typically shows a sharp zone of transition with little or no rim of reactive sclerosis. When lesions erode the inner and outer tables of the calvarium to a different degree, the margins of the cal-varial defect are said to be beveled. Lesions arising external to the calvarium typically erode the outer table more than the inner table and are ‘beveled-from-without’. Such lesions include anterior fontanelle dermoids, some stages of cephalhematoma deformans and eosinophilic granuloma. Other lesions erode the inner table more