A Commentary on the Lead Positioning for Deep Brain Stimulation in the Pedunculopontine Tegmental Nucleus in a Patient Affected by Multiple System Atrophy

Identification of the position of the leads in the PPTg is problematic for a number of reasons that we extensively discussed in our recent review [6] . Briefly, the human brainstem has a high degree of variability from patient to patient; thus, the traditional stereotactic identification of a target based on ventriculography and evaluation of the Ca-Cp line cannot be adopted. Furthermore, the PPTg is only partly represented in the classic Schaltembrand and Wahren’s stereotactic atlas [7] , while other reconstructions of the position of the PPTg [8] do not provide a detailed description of the structures surrounding the PPTg and extend the nucleus into the lower mesencephalon rather than below the pontomesencephalic junction. One way to overcome these limitations is to combine the axial plates reported in Paxinos and Huang’s human brainstem atlas [9] with postoperative MRIs, in which the lead contacts may be appreciated. The lower and central portions of the PPTg, which are reported in Paxinos and Huang’s plates, are useful for checking the spatial relationships between the discrete structures present in the targeted region and the location of the leads. The case report by Acar et al. [1] recently published in Stereotactic and Functional Neurosurgery, as do other similar case reports [2, 3] populating the literature concerning deep brain stimulation (DBS) of the pedunculopontine tegmental nucleus (PPTg), demonstrates the growing interest of neurosurgeons in the use of new neurosurgical targets for the treatment of movement disorders in drug-resistant patients. Such an interest is especially prompted by the need to treat symptoms for which traditional stimulation of the subthalamic nucleus has given unsatisfactory results [4–6] , such as gait freezing and postural instability. Undoubtedly, the efforts that several groups have devoted to this issue deserve to be appreciated. However, skepticism remains when observations are sporadic and carried out on a single case or on a few patients, who are often not affected by Parkinson’s disease (PD) but rather by parkinsonian syndromes such as progressive supranuclear palsy and multiple system atrophy. The patient implanted in the PPTg by Acar et al. [1] suffered from multiple system atrophy. In this pathology, neither medical therapy nor neurosurgery of traditional targets improves motor signs; thus, the hope was that PPTg DBS would have a positive outcome, which did not occur. Although currently there is no convincing evidence to show that PPTg DBS may be of benefit in such parkinsonian syndromes, improper positioning of the stimulating leads in the PPTg may cause inconsistencies in the evaluation of clinical outcome. We wish to point out that the axial slices of postoperative MRIs presented by Acar et al. [1] ( fig. 1 , 2 ) show a position of the stimulating tip that clearly differs from the region ( fig. 3 ) that we targeted in the 27 patients so far implanted in our experience. Received: September 6, 2011 Accepted: October 17, 2011 Published online: March 2, 2012