PNist is a new method for the semiautomatic segmentation of PN lesions. Its simplicity and reliability make it unique among other state-of-the-art methods. It has the potential to become a clinical tool that allows the reliable evaluation of PN burden and progression.

Th e commo n neopl asms of shee p include intestina l ade no carcino ma [1,6,14] and lymphosarco ma and hepatic ca rcino ma [1,5,14]. Th ere are few report s of neopl asms arising in nervou s tissue in sheep. Aba tto ir survey dat a generally do not ment ion tum ors of th e cen tra l nervous system [I,3, II ,14]. Review ar ticles also lack inform ati on on centra l nervou s system tum ors of sheep [8,12,13]. Menin giom a, perineural fib robl astom a and adventitia l sa rcomas [91 , cerebra l hem an giom a astroc ytoma and intercos ta l neu rofibr om a [4] and spinal melan om a [2J ha ve been reported in shee p.A 9-mo nth-old fema le Hampsh ire shee p was sub mitted to th e Sch ool of Veterinary Med icine's Diagnostic Lab or at ory, Ore gon State U niversity. Fo r th e previous mo nth th e shee p had refused to stand . T he owners had d ren ched th e shee p with egg yo lk and sugar, and had prov ided hay an d oa ts. At necropsy th ere was a firm white-tan 2-to 3-centime ter ovo id no dule on the ven tral surface of th e anterio r cervical spina l cord at the atlantal-occipi tal articulation ( fig. I). Ne rves did no t extend from the tum or. On section, th e tumor 's exp an sion had resulted in seve re co mpressio n atro phy of th e adj acent spina l cord ( fig. 2). T issue was fixed in 10% buffe red formalin and hem atoxylin and eosin (HE) -stained 6-microme ter sections were pre pared.T he tumo r was composed of numerous interl acing bundles of elonga te ba sophilic nuclei embedded in an abundant eosi no phi lic cytoplasm ic mat rix ( fig. 3). Ce ll bord ers were not distin ct. Th e nuclei varied in chroma tin density, but nucl eoli and mitot ic figures were uncommon . N ucle i were consisten tly a ligned in parall el ar rays, but palisading was rar e. Specia l stains showed a mod erat e amo unt of collage n, mainly restric ted to th e ed ges of th e cell-rich anastomosing bundles. Reticul in was not prom inent. T here was no evidence of necrosis, hemorrhage, miner alization, inl1amm ation or enca psulatio n. U ltras truc tural exa mination of form alin-fixed tissues was unrewarding becau se of fixation ar tifacts .

Our study suggests that the new PNist method is accurate, intuitive, and less time consuming for PN segmentation compared to existing commercial volumetric methods. The workflow is simple and user-friendly, making it an important clinical tool to be used by radiologists, neurologists and neurosurgeons on a daily basis, helping them deal with the complex task of evaluating PN burden and progression.

The original version of this paper unfortunately contained error. Figure 1c is incorrect and should be replaced by the following Fig. 1c: The online version of the original article can be found at http://dx