Hearing preservation after gamma knife stereotactic radiosurgery of vestibular schwannoma

Abstract

We studied the distributions of interneurons containing the calcium‐binding proteins parvalbumin and calbindin D‐28k, as well as that of pyramidal neurons containing nonphosphorylated neurofilament (NNF), in the middle temporal visual area (MT) of marmoset monkeys. The distributions of these classes of cells in MT are distinct from those found in adjacent areas. Similar to the primary visual area (V1), in MT, calbindin‐immunopositive neurons can be objectively classified into “dark” and “light” subtypes based on optical density of stained cell bodies. Calbindin‐positive dark neurons are particularly concentrated in layers 2 and 3, whereas light neurons have a more widespread distribution. In addition, a subcategory of calbindin‐positive dark neuron, characterized by a “halo” of stained processes surrounding the cell body, is found within and around layer 4 of MT and V1. These cells are rare in most other visual areas. In comparison, parvalbumin‐immunopositive cells in area MT have a relatively homogeneous distribution, although with a trend toward higher spatial density in lower layer 3, and are relatively uniform in terms of density of staining. Finally, MT shows a characteristic trilaminar distribution of NNF‐immunopositive pyramidal cells, with stained cell bodies evident in layers 3, 5, and 6. Although the laminar distribution of cells stained for the three markers overlap to some extent, these subcategories can be readily distinguished in terms of morphology, including cell body size. Chemoarchitectural parallels observed between MT and V1 suggest comparable physiological requirements and neuronal circuitry. J. Comp. Neurol. 500:832–849, 2007. © 2006 Wiley‐Liss, Inc.

Radiosurgical treatment of vestibular schwannomas in patients with neurofibromatosis type 2

“…[25][26][27] Although we observed no significant effect of cochlear doses in the current study, this issue deserves further investigation in a larger series.…”

“…25 Facial neuropathy, both transient and permanent, occurred in 2.8% of tumor-affected sides in this study. This figure is similar to that of the low-dose treatment group in the study by Rowe et al 11 (Table 3).…”

“…It is well known that lowdose (12-13 Gy) radiosurgery results in better hearing preservation for sporadic vestibular schwannomas. 24,25 Therefore, it could be a reasonable radiosurgical strategy in NF2 patients to apply low doses (12-13 Gy) for hearing preservation and slightly higher doses to tumors without ipsilateral hearing for better tumor control.…”

Clinical outcome after Hypofractionated Stereotactic Radiotherapy (HSRT) for benign skull base tumors

“…Ito et al reported that 69% of patients who underwent radiosurgery (median dose: 16.8 Gy) for acoustic neuroma exhibited pure tone average (PTA) elevation of >20 decibels (dB), suggesting hearing loss after treatment [16]. Similarly, Paek et al reported that 16/25 patients (64%) with serviceable hearing pre-treatment suffered hearing loss of >20 dB after radiosurgery (12 Gy at the 50% isodose) [17].…”

“…Modern singlefraction SRS has been associated with a 10-40% risk of cranial nerve damage in some series [14,15], and the incidence has been reported to be as high as 60% when qualitative hearing assessments are used [16,17]. On the other hand, a conventional fractionated radiation therapy regime with 30-33 treatments over 5-6 weeks is very rarely associated with neurological toxicity [18][19][20][21].…”