Microadenomi ipofisari: Aspetti RM

Abstract

RIA SSUNTO -La RM per le sue caratteristiche specifiche ed uniche ha sostituito la TC nello studio della patologia ipofisaria in genere e dei microadenomi in particolare. La RM consente infatti nella pressoche totalita dei casi di accertare la presenza di un microadenoma di cui inoltre ne consente un agevole monitoraggio in corso di terapia medica e dopo terapia chirurgica.La diagnostica RM dei microadenomi si avvale dell'impiego combinato di sequenze T2 e Tl prima e dopo mdc e di sequenze dinamiche in corso di iniezione di mdc: l'accertamento di microadenoma e in funzione della presenza di segni RM diretti ed indiretti. Nei rari casi per i quali la diagnostica RM non consente una diagnosi sicura e specie se esiste il sospetto di adenomi a secrezione ACTH e indicato il ricorso al cateterismo dei seni petrosi. La TC potrebbe essere utilizzata esclusivamente nei casi che per differenti ragioni non possono giovarsi dell'impiego della RM. Pituitary Microadenomas: MR FeaturesSUMMARY -Pituitary tumours constitute about 10-15% of intracranial tumours. Neuroradiologically, they are termed microadenomas when their diameter is less than 10 mm and macroadenomas when larger. Adenoma cell differentiation affects the immunohistochemical features of adenomas permitting a distinction between functional secreting adenomas and non-functioning adenomas. Overall, microadenomas secreting prolactin are the most common, followed by non-functioning tumours, adenomas secreting GH, those with mixed secretion, tumours secreting ACTH and lastly, rare TSH-secreting adenomas. In almost all cases they are benign tumours, even though there is a tendency towards local invasion. Malignancy and metastases are exceptional. MR has replaced CT in the study of microadenomas as in most cases it will identify the tumour directly as a small signal abnormality and indirectly through the effects on the healthy pituitary gland and its stalk. MR is usually performed combining T2 and T1 weighted scans and dynamic techniques during injection of contrast administration at normal or reduced doses .In general, microadenomas are depicted in T1 scans as a signal hypointensity accentuating during and after contrast injection. However, microadenomas largely isointense to the pituitary parenchyma, microadenomas spontaneously hyperintense if bleeding and microadenomas hyperintense soon after contrast administration are also encountered. In T2 sequences, spontaneous, often heterogeneous, hyperintensity of the microadenoma is often seen. The main indirect signs of a microadenoma include erosion of the sellar floor, raised superior pituitary profile and changes in the medial profile of the cavernous sinus on the side of the microadenoma as well as displacement of the pituitary stalk contralateral to the adenoma site. Without direct signs, indirect signs alone preclude final diagnosis of microadenoma. Differential diagnosis of microadenomas includes intermediate cysts, Rathke's cleft cysts and intrasellar craniopharyngioma. Benign aspecific focal signal abnormalities in th...