Risonanza magnetica

 Torno sull'argomento del ricovero a neurologia a Lecce, e sull'aver atteso di effettuare una risonanza magnetica al cervello. Un apparecchio per la risonanza è presente nella struttura, quindi occorre entrare nella lista di attesa, che spesso viene disattesa per ricoveri in urgenza che hanno la precedenza. In reparto eravamo almeno in due, come ricoverati, in attesa di venire sottoposti all'imaging. 

Prima di tutto, soggettivamente l'esame è stato complicato dalla reazione del corpo alla stimolazione acustica. Si viene immessi in un alloggiamento chiuso, oppressivo, sormontati da una calotta tipo coperchio di bara. Le onde sonore sono di vario tipo, più procede l'esame più diventano rimbombanti. Il corpo ha reagito male, tipo iniziali conati di vomito, che ho soppresso pensando che sarei stato dimesso grazie a questo referto, ho resistito fino ad esaurimento nervoso (quasi).

Questo esame viene facilitato dalla somministrazione di un liquido di contrasto, spesso contenente gadolinio complessato a composti chelanti.

Gadolinium is a rare-earth metal of the lanthanide series with atomic number 64 in the periodic table of elements. Given its highly paramagnetic properties, it is used as a component of contrast agents administered during magnetic resonance (MR) imaging and angiography procedures. Because gadolinium is highly toxic in its free form, it is bound to an organic chelate when used as a contrast agent. The preparations of GBCAs that are administered during imaging procedures contain the gadolinium–chelate complex with variable amounts of excess chelate added to bind free gadolinium that is released from its chelate while stored in the bottle.

Commercially available GBCAs differ in the structure of their chelate (macrocyclic vs. linear) and in their charge (ionic vs. non-ionic). These properties determine the ease with which free gadolinium is released from the gadolinium–chelate complex. Whereas ionic and macrocyclic agents have the highest affinity for gadolinium, the risk of gadolinium dissociating from its chelate increases for non-ionic and linear agents

La metodologia del functional Brain Magnetic Resonance Imaging (fMRI) si applica per il rilevamento di tumori nel cervello, per l'identificazione delle aree da sezionare con chirurgia.

Brain magnetic resonance imaging (MRI) demonstrated the presence of a right middle cingulate tumor extending into the superior frontal gyrus, with radiological characteristics in keeping with diffuse astrocytoma (Fig. 1A-B-C). Although there was no pathological gadolinium enhancement, there were some areas of restricted diffusivity within the tumor suggestive of possible higher-grade transformation.

Fig. 1. Coronal (A), Sagittal (B) and Axial (C) FLuid Attenuated Inversion Recovery (FLAIR) images demonstrating a hyper-intense lesion in the cingulate region with radiological features suggestive of low grade glioma. These images were obtained intra-operatively and the green cross hair corresponds approximately to the point of monopolar stimulation of the cingulate cortex following tumour resection. D,E,F: Montreal Neurological Institute (MNI) coordinates as obtained from the online atlas.

In questo articolo, D'Urso PI, Lodwick S, Pereira N, Ponnusamy A. Cingulate motor areas: Intraoperative findings. Clin Neurophysiol. 2020 Aug;131(8):1804-1805) i neurochirurghi riportano sul metodo per l'eliminazione di un astrocitoma.

Herein, we document our intraoperative electrophysiological findings in a case of diffuse astrocytoma of the right mid-cingulate gyrus.

A 79-year-old patient presented to our Neurosurgery department with left leg dyspraxia and numbness. On examination she had grade 4/5 weakness and increased reflexes in her left leg.

  The stimulation point corresponds to Broadman Area 23. Our stimulation point appears to be slightly more posterior to the mid-cingulate areas described on fMRI studies, but this is believed to be related to the fact that the normal anatomy in our case was distorted by the presence of the tumour.

We have reported the case of a patient affected by diffuse astrocytoma of the right cingulate gyrus who underwent resection with intraoperative neurophysiology mapping and monitoring. During the resection, cortico-spinal tracts for the upper limb were activated both from motor cortex stimulation as well as cingulate cortex stimulation. It is to be noted that during cingulate cortex stimulation the MEP responses were limited to the contralateral Abductor Digiti Minimi (ADM) and First Dorsal Interosseous (FDI) in the upper limb: despite the medial location, no MEPs were elicited from the lower limb. This proves that the response primarily resulted from stimulation of the cingulate cortex stimulation rather than from stimulation of the medial and lateral part of the CST. The area of stimulation corresponds to cingulate areas highlighted in previous functional MRI studies.

Fig. 2. A. Motor evoked potential (MEP) from motor cortex stimulation (white arrow: latency 23.5 ms). B: MEP from cingulate stimulation (white arrow: latency 25.9 ms).