title: Atypical Neurocytoma: Dilemma in diagnosis and management.
abstract: BACKGROUND
  Central neurocytoma is an uncommon benign tumor of the central nervous system. A section of these tumors have unusual aggressiveness and are termed as "atypical central neurocytomas," the definition of which is debated. Many studies in the available literature define them as tumors with elevated MIB-1 labeling index (MIB-1 LI) >2%, while some associate them with higher values of MIB-1 LI or those with histological atypical features. Newer parameters also have been identified and correlated with MIB-1 LI to differentiate atypical from benign neurocytoma cases. A recent analysis of the atypical neurocytoma cases with malignant behavior revealed their increased tendency of spread through the cerebrospinal fluid causing craniospinal axis dissemination. However, limited studies document the appropriate indications and usefulness of additional therapeutic modalities, such as upfront craniospinal irradiation (CSI) or adjuvant chemotherapy, in countering the aggressive behavior of such tumors.
  
  
  METHODS
  We present two such rare cases of atypical neurocytoma with elevated MIB-1 LI, of 3% and 4%, respectively, without histological atypia. Since there is insufficient evidence documenting advantages of any additional measures in the adjuvant management of atypical cases, both patients were treated with localized cranial radiotherapy alone, as per the evidence available in the literature currently.
  
  
  CONCLUSIONS
  We propose that future studies must aptly redefine these atypical neurocytomas with malignant potential and provide guidance to identify aggressiveness of these tumors early in the course of management. Lastly, strong evidence to provide specific adjuvant therapy is also warranted.
authors.affiliation: Department of Radiation Oncology, Krishna Institute of Medical Sciences, (KIMS), Secunderabad, Andhra Pradesh, India.
authors.forename: Gangadhar
authors.initials: G
authors.lastname: Vajrala
authors.affiliation: Department of Radiation Oncology, Krishna Institute of Medical Sciences, (KIMS), Secunderabad, Andhra Pradesh, India.
authors.forename: Piyush K
authors.initials: PK
authors.lastname: Jain
authors.affiliation: Department of Radiation Oncology, Krishna Institute of Medical Sciences, (KIMS), Secunderabad, Andhra Pradesh, India.
authors.forename: Shitalkumar
authors.initials: S
authors.lastname: Surana
authors.affiliation: Department of Pathology, Krishna Institute of Medical Sciences, (KIMS), Secunderabad, Andhra Pradesh, India.
authors.forename: Sailaja
authors.initials: S
authors.lastname: Madigubba
authors.affiliation: Department of Pathology, Krishna Institute of Medical Sciences, (KIMS), Secunderabad, Andhra Pradesh, India.
authors.forename: Satish R
authors.initials: SR
authors.lastname: Immaneni
authors.affiliation: Department of Neurosurgery, Krishna Institute of Medical Sciences, (KIMS), Secunderabad, Andhra Pradesh, India.
authors.forename: Manas K
authors.initials: MK
authors.lastname: Panigrahi
keywords: Atypical neurocytoma; MIB labeling index; cerebrospinal fluid dissemination; chemotherapy; craniospinal irradiation; malignant; radiotherapy