A posterior fossa tumour (PFT), and its subsequent treatment, has the potential to cause disruption to the functioning of the oromotor mechanism and speech production process in a child resulting in the motor speech disorder of dysarthria and/ or the swallowing disorder of dysphagia. Literature to-date has focused primarily on the acute presentation of these disorders in the PFT population with a paucity of attention to the persistent long-term characteristics. The dysarthria has been found to be an on-going sequelae of treatment for some children treated for PFT and the impact of this disorder, even to a mild degree can impact on a child's interactions with their peers. The primary aim of the current thesis is to profile the perceptual & acoustic characteristics of the dysarthric speech disturbance exhibited by a group of children treated for PFT, and examine the physiological features that underlie this disorder.
A total of 25 children treated for PFT were included in the current project along with a group of non-neurologically impaired control subjects, matched for age and sex. The PFT group consisted of 21 children with cerebellar tumour following initial treatment (CT), two children with brainstem tumours, one child with a recurrent cerebellar tumour and one child treated for a fourth ventricle choroid plexus papilloma. All PFT participants were at least six months post-treatment. All participants were assessed on a range of perceptual measures, with acoustic and physiological measures used to compliment the perceptual procedures.
Initially, the speech of the group of 21 CT participants was assessed using a comprehensive battery of perceptual assessment procedures including deviant speech feature analysis, speech intelligibility measures and oromotor function. The CT group was found to consist of both dysarthric (11) and non-dysarthric (10) participants and comparisons on each of the assessment measures with the control group were made for both the dysarthric (DCT) and non-dysarthric (NDCT). The DCT participants were found to be significantly less intelligible than the controls and impaired in three of the five aspects of speech production (phonation, articulation and prosody). These disturbances of phonation, articulation and prosody were accompanied by oromotor dysfunction in non-speech and speech tasks assessing laryngeal, lip and tongue function. The NDCT participants were found to perform similarly to the controls of most assessment measures. The results of the DCT groups are discussed in relation to the variability within the group, the effects of cerebellar damage on speech production, and similarities and differences between the dysarthria seen m the CT children when compared to adults with ataxic dysarthria caused by cerebellar damage.
To provide an objective measure of the phonatory impairments noted in the DCT participants, an acoustic examination of vocal quality was performed on nine of the DCT group and compared to the non-neurologically impaired controls. The acoustic voice analysis confirmed the presence of phonatory disturbance with increased values for frequency and amplitude perturbation, both in short term and long-term measures, as well as voice breaks. The perceptual characteristics of the DCT group's voices (roughness, instability and breathiness) were found to relate well with a cluster model of acoustic voice parameters proposed by Dejonckere et al. (1996). The results are discussed by interpreting the perceptual voice characteristics in relation to the acoustic findings, as well as possible physiological implications inferred by the acoustic analysis. The need for further physiological examination of laryngeal function was suggested.
To ascertain the nature of any physiological impairment that may impact on the CT participants' speech production ability the respiratory, laryngeal, velopharyngeal and articulatory subsystems of the speech mechanism were evaluated separately using instrumental procedures. The speech respiration ability of five CT children, laryngeal function of six CT participants, and velopharyngeal and articulatory abilities of seven CT children from the larger group of CT participants were assessed. Group analyses were performed for each of the examinations of the speech subsystems, along with individual case analyses due to small subject numbers and variability with regard to the diagnosis of dysarthria within these small groups. TTie group analyses for speech respiration and laryngeal function did not identify any significant difference in performance between the CT groups and controls; however, individual case analyses particularly for those children with dysarthria did identify some evidence of laryngeal impairment. Group analyses for velopharyngeal and articulatory function revealed significant differences between the CT and control groups. The individual case analyses raised some concerns regarding the validity of the group result for velopharyngeal function finding only one of the CT participants had nasalance scores indicative of impairment to the velopharyngeal mechanism. All results were discussed in relation to the perceptual profiles for the CT children, the variability within the small groups, and the possible links between the mechanisms of cerebellar damage and the neuromuscular impairments found.
The posterior cranial fossa as an anatomical structure contains more components of the central nervous system than the cerebellum, including the brainstem and fourth ventricle. Most of the current study to this point has focused on children treated for initial diagnosis of CT, a further four participants treated for PFT were included in the current study. These four case studies allowed for examination of motor speech and oromotor functioning in children with fourth ventricle, brainstem and recurrent cerebellar tumours. Two participants had both persistent dysarthria and dysphagia, while the remaining two children had been treated for brainstem tumours. All four participants underwent the complete perceptual physiological assessment battery, while the two participants with dysphagia also had videofluoroscopic examinations of swallowing completed. The results for the two participants with both dysarthria and dysphagia indicated that they had a dysarthria marked predominantly by laryngeal impairment, while the dysphagia was resultant from difficuties at all three stages of the swallow (oral preparatory, oral, and pharyngeal). The results for the two children treated for brainstem tumours found that dysarthria was evident in only one of the participants. This child exhibited deviant speech characteristics related to phonation, articulation, resonance and prosody, as well as unresolved developmental speech errors. The results for all four cases are discussed m relation to the sites of neurological damage and possible physiological mechanisms that could be associated with their speech production and m two cases, their dysphagia.
The current series of studies has served to document the variable nature of the impact the PFT and its treatment can have on the speech and swallowing abilities of children. The findings are discussed with respect to the heterogeneous nature of PFT participants, the effects of cerebellar or lower motor neuron damage on the speech production mechanism, the need for objective, instrumental assessment of the motor speech subsystems to support perceptual findings, the importance of evaluating the assessment results on an individual basis, and the need for consideration of the on-going neuromuscular development of child's speech mechanism. Directions for future research are suggested in relation to many of these issues to continue to build our knowledge base regarding acquired childhood dysarthria.