Dear Editor:We would like to thank Gudrunardottir and coworkers forcommenting on our paper “Fronto-cerebellar fiber tractographyin pediatric patients following posterior fossa tumor surgery”[1]. We admit that the paper entitled “Cerebellar mutism:review of the literature” by Gudrunardottir et al. [2] shouldhave been cited at the respective passage instead of or eventogether with “Cerebellar mutism: definitions, classificationand grading of symptoms” by the same group [ 3]whichwere published both in 2011.The issue raised by Gudrunardottir et al. is the ambiguoususe of the term of “cerebellar mutism (CM)” and its exactdefinition. In our report, we used CM and CM syndrome(CMS)assynonymsandtherebymaynothaveclearlyenoughexpressed that we agree that posterior fossa syndrome (PFS)describes a broader symptomatology complex of which CMSorCMisanintegralpart.Inthiscontextandtobetterelucidatethe problem of inconsistent terminology, we scrutinized theterminology used in the literature in the period between 2000and2013byperformingaMedlinesearchusingthephrases“cerebellar mutism” and “cerebellar mutism syndrome.” Weexcluded all non-English papers and all publications, whichdid not primarily deal with cerebellar pathology. The searchrevealed 86 publications: 12 reviews, 13 letters to the editors,26 case reports, and 35 original papers. Among these, weevaluated the terminology used for the clinical picture dealingwith mutism caused by cerebellar pathology. Eventually, wefound up to nine different specifications (Table 1). The major-ity of papers used only one or two terms (n=57) for thesymptomatology. The mean number of terms used was 2.2ranging from one up to five terms per paper. CM and CMSwere used most often as synonyms (n=14). Even more con-fusing synonymous descriptions were CM together with“posterior fossa syndrome” (n=5) or together with“akinetic mutism” (n=4). In contrast, clear delineation be-tween the terms CM and CMS was performed in onlyseven publications.This wide spectrum of terms employed clearly shows thatthe definition of CM and its associated syndromes is stillwithout clear definition. Thus, wesupport theneedfor a clearandwidelyacceptedterminologyproposedbyGudrunardottiret al. [3]. We agree with their definition of CM as a mutenessfollowing lesion of the cerebellum as opposed to occurrencewith lesions of the cerebrum or the lower cranial nerves. WealsoagreethatCMisonlyonesymptomoftheCMScomplexthatalsoincludesataxia,hypotonia,andirritabilityorthatCMand CMS are part of PFS that additionally includes cranialnervedeficits,neurobehavioralchanges,andurinaryretentionor incontinence [3]. In our view for future discussions, threeissues need further clarification: firstly, any symptoms ofdecreasedimpetusmaybebetterclassifiedwithinCMSratherthaninthecontextofPFSasproposedbyGudrunardottiretal.[3].Thisincludesimpairedimpulsionofmotormovements(aslong as no brainstem lesion is present) or impaired impulsionof eye opening, which may be similar in its cerebellar originlike impaired impulsion of speech production. Secondly,neurobehavioral changes like apathy and deficits of atten-tion or memory may resemble lack of cerebellar controlon higher prefrontal function, which is yet not fully un-derstood. As long as anatomical correlates are not clearlyidentified, an exact and sustainable terminology cannot befound. Nevertheless, it seems reasonable to distinguishCMS with neurological deficits being related to cerebellarfunctions from PFS that includes symptoms related tocranial nerves or brainstem deficits. Thirdly, grading ofseverity of CMS is still ill defined. Robertson et al. usedthe duration of symptoms as a measure for severity [4].The future goal may be to grade the severity of mutenessitself as well as to grade the amount of symptoms withinCMS. This may be relevant to evaluate even mild