The shrinkage of the human brain stem during formalin fixation and embedding in paraffin

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Abstract

On the basis of measurements on fresh human brains (n=33), changes in size of the brain stem which occurred as a result of formalin fixation and embedding in paraffin were quantified and converted into linear correction factors. In contrast to the known changes in the cerebrum, the formalin fixation did not result in a `positive formalin effect', but left transverse values unchanged and led to decreases in longitudinal distances of 1–8% (correction factors: 1.01–1.09). Further embedding resulted in a linear shrinkage of 11–12% (correction factors: 1.12–1.13) transversely and 17% (correction factor: 1.21) longitudinally, which was smaller than the shrinkage in the cerebrum of 11–25% (correction factors: 1.13–1.34) reported in the literature. The examinations revealed changes in the brain stem caused by the total fixation and embedding process different from those of the cerebrum.

Introduction

The development of microsurgical approaches to place electrodes in the area of ventral and dorsal cochlear nuclei for electric stimulation requires a detailed topo-anatomic knowledge of the exact extension of the nuclei surface at the base of the IVth ventricle and in the area of Luschka's foramen adjacent to the caudal end of the inferior cerebellar peduncle. This can only be reached by histological examination of these structures.

For the reconstruction of these dimensions in paraffin section series of formalin-fixed brain stem preparations, the exact evaluation of the shrinkage factors for formalin fixation and embedding in paraffin is necessary. Although several examinations concerning shrinkage behaviour of tissue have been published in the literature, they were mostly carried out on liver, muscle, spleen or kidney tissues (Bahr et al., 1957; Bloom and Friberg, 1956; Seki, 1937; Stoeltzner, 1906; Stowell, 1941; Wüstenfeld, 1954). Those examinations carried out on brain tissue mainly referred to the cerebral hemispheres and partly to the cerebellum. A literature review revealed no comparable investigations concerning the brain stem. These studies only partially relate to human tissue. Frequently, animal species such as guinea-pig, rat, cat or cow were examined in which other shrinkage factors can occur (Bahr et al., 1957; Blinkov and Glezer, 1968; Fischer et al., 1973; Flatau, 1897; Gellért, 1971; Haug, 1980; Hillman and Deutsch, 1978; Kato, 1939; Kretschmann et al., 1982; Lagerlöf and Torgersruud, 1934; Leibnitz, 1967; Leibnitz, 1971,1972; Mouritzen Dam, 1979; Sarkissow, 1930; Schremmer, 1967; Stephan, 1960; Stoeltzner, 1906; Treff and Kraus, 1960). In addition, it has not yet been proved whether the results of the investigations in the human cerebrum can simply be transferred to the brain stem. There might be differences owing to the different anatomic structures (Leibnitz, 1971,1972).

Section snippets

Materials and methods

Thirty-three brain stems from the regular autopsy material were examined: 29 male and four female cases, aged between 15 and 79 years. The brains did not show any pathological changes such as traumatic injuries, massive bleedings, meningitides, system or tumour diseases or degenerative diseases. Metabolic disturbances and brain edema were also excluded.

The autopsy was usually carried out 1–2 days post mortem and performed as follows: the brain was obliquely separated at the level of the

Results

Measurements on the fresh brain stem resulted in 1.79 cm as the maximum breadth at the olive level (range: 1.65–2.00 cm, s=0.88, n=17). The longitudinal measurements for the right olive resulted in 1.59 cm (range: 1.18–1.91 cm, s=0.18, n=14), for the left olive 1.53 cm (range: 1.30–2.00 cm, s=0.22, n=9), for the ventral conus 2.91 cm (range: 2.20–3.90 cm, s=0.58, n=17) and for the dorsal conus 4.10 cm (range: 3.42–5.05 cm, s=0.46, n=14). These values are reference values for the changes caused

Discussion

Topoanatomic measurements of brain structures are usually performed on formalin fixed preparations or section series after embedding in paraffin. Both processes lead to changes in size. The determination of correction factors is therefore necessary in order to be able to calculate back to values of fresh brain tissue.

The effects of formaldehyde on the human cerebrum have been described to result in a maximum increase in weight and volume between the first and fifth day, which decreases during

Acknowledgements

The investigations were performed with the support of the Federal Ministry of Education, Science, Research and Technology, reference number 01 VJ 9310/1.

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