- Email: [email protected]
Freezing effect on brain density in postmortem CT
Legal Medicine 18 (2016) 62–65
Contents lists available at ScienceDirect
Legal Medicine journal homepage: www.elsevier.com/locate/legalmed
Case Report
Freezing effect on brain density in postmortem CT Miyu Sugimoto, Hideki Hyodoh ⇑, Masumi Rokukawa, Ayumi Kanazawa, Rina Murakami, Junya Shimizu, Shunichiro Okazaki, Keisuke Mizuo, Satoshi Watanabe Department of Legal Medicine, Sapporo Medical University, S1 W17 Chuo-ku, Sapporo 060-8556, Japan
a r t i c l e
i n f o
Article history: Received 15 November 2015 Received in revised form 16 December 2015 Accepted 17 December 2015 Available online 18 December 2015 Keywords: Postmortem CT Freezing effect Postmortem change Forensic radiology Low density
a b s t r a c t Two 60-year-old males were found at their homes whose bodies had deteriorated due to putrefaction. To prevent worm invasion and minimize deterioration, dry ice was used prior to the autopsy investigation. Prior to autopsy, postmortem CT demonstrated a decreased density in brain parenchyma at the dry-iced side, and autopsy revealed deteriorated brain parenchyma with frozen effect (presented like sherbet). Moreover, the deteriorated cerebral parenchyma maintained their structure and they were evaluated by cutting. When lower CT density presents in postmortem CT, the freezing effect may need to be considered and the physician should evaluate the cadaver’s postmortem condition to prevent misdiagnoses. Ó 2015 Elsevier Ireland Ltd. All rights reserved.
1. Introduction
2. Case 1
One of the recent topics of interest in legal medicine is postmortem CT, and many postmortem CT studies have been reported prior to postmortem investigation and/or full-autopsy examination [1–3]. Thali et al. [4] reported the usefulness of postmortem computed tomography (CT) to evaluate the cadaver objectively and with surface scan technique; they named it ‘‘Virtopsy”. The usefulness of postmortem CT has been reported, and in recent years, postmortem CT angiography has also been reported, and identified the causes of death in certain cases [5,6]. However, in situations when knowledge regarding postmortem image changes and the background of the cadaver is lacking, the precise interpretation of postmortem CT is difficult and it might result in incorrect conclusion [7]. Even if a CT image contains specific findings which seem to point to a clear conclusion, if the physician does not have knowledge of postmortem change, the apparent conclusion may be incorrect [7,8]. In this report, we present our finding of a lower density region on postmortem brain CT, which proved to be the effect of frozen tissue on autopsy examination. We investigate its mechanism and report this new pitfall in postmortem CT investigation. To verify the lower CT density in brain, we examined an additional ex vivo experiment.
A 60-year-old male (165.0 cm, 29.2 kg) was found dead in his room. The cadaver was lying on the bed without any extrinsic injury. Before the scheduled autopsy (2 days later), the cadaver was surrounded by dry ice to prevent worm invasion and minimize deterioration. Prior to autopsy, postmortem CT was used to monitor the internal change and to record the pre-autopsy condition. Postmortem whole body CT was performed using a 64-slice multi-detector CT scanner (Aquilion CX, Toshiba, Tochigi, Japan). Neck to head; 120 kV, 300 mA, 1.0 s/rotation, pitch factor 0.641, configuration 0.5 32, reconstruction 0.5 mm, MPR (multi-planar reformation) image reconstruction: 5 mm in the axial sections. Neck to foot; 120 kV, 50–400 mA (variable mA), 0.5 s/rotation, pitch factor 0.828, configuration 0.5 32, MPR (multi-planar reformation) image reconstruction: 7 mm in the axial sections. On postmortem CT, free air was detected in the cranium, and different densities were detected in the deteriorated brain parenchyma (19.4 ± 5.4 HU and 40.9 ± 4.4 HU), which appeared to exhibit decreased brain parenchymal density at the dry-iced side (Fig. 1a). An autopsy revealed deterioration in the brain parenchyma on the right side, but less deterioration on the left side (Fig. 1b). After cutting the parenchyma, the left-side cerebral parenchyma was frozen and presented like sherbet. No hematoma or infarction was detected in the brain autopsy. The postmortem CT also presented pneumothorax in the left pleural cavity, and its volume was 4.2 L (Fig. 1c). The mediastinum was shifted to the right side, which might be the cause of the
⇑ Corresponding author. E-mail address: [email protected] (H. Hyodoh). http://dx.doi.org/10.1016/j.legalmed.2015.12.007 1344-6223/Ó 2015 Elsevier Ireland Ltd. All rights reserved.
M. Sugimoto et al. / Legal Medicine 18 (2016) 62–65
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Fig. 1. A 60-year-old male found in his room; (a) postmortem brain CT, (b) macroscopic brain photography (view from the top), and (c) postmortem chest CT. (a) Intracranial and intravascular air density is demonstrated due to putrefaction. The shifted brain parenchyma shows layered densities; 19.4 ± 5.4 HU at the left side, and 40.9 ± 4.4 HU at the right side. (b) The right-side brain parenchyma deteriorated, but the left-side brain parenchyma kept its shape. The left-side brain parenchyma can be evaluated by cutting and it seems sherbet-like parenchyma. (c) Large free-air density (4.2 L) in the left pleural cavity, right-side shifted mediastinum, and right pleural space fluid collection (420 mL) is demonstrated. An autopsy proves no other causes of death, and tension pneumothorax is thought to be the cause of death.
respiratory and circulatory dysfunction. An autopsy revealed convex deformation of the left diaphragm to the abdominal cavity, left lung contraction, and right-sided mediastinum deviation. Consequently, the cause of death was diagnosed as respiratory and circulatory dysfunction due to the left tension pneumothorax.
tissue was frozen and the parenchyma presented like sherbet. No hematoma or infarction was revealed in the brain autopsy. Consequently, the cause of death was designated as unknown.
3. Case 2
This ex-vivo study was not needed to approve our institutional animal ethics committee. Commercially available extracted pig brain tissue (Hokkaido Wako Pure Chemical Industries, Ltd. Sapporo) was put into a sealed bag and placed on the dry-ice. The tissue was placed in the CT room (20 °C) through the whole observation period, and the whole tissue was examined by CT. Before and after freezing, a CT examination was performed in the same scanner using the following protocol: 120 kV, 200 mA, 0.5 s/rotation, pitch factor 0.641, configuration 0.5 32, reconstruction 0.5 mm. The pig brain parenchyma showed lower density after freezing (Fig. 3a and b). Comparing the CT numbers before and after freezing, the brain tissue has decreased its density from 72.6 ± 1.4 HU to 6.5 ± 1.5 HU. The cut surface presented like sherbet, macroscopically (Fig. 3c).
A 60-year-old male (167.7 cm, 51.8 kg) was found dead in his room. Because a stench had been noticed, a police investigator was requested to gain admittance to his room, and found the cadaver lying on the bed without any extrinsic injury. There were many worms in the cadaver. For personal identification and to investigate the cause of death, an autopsy was scheduled. To minimize deterioration and worm invasion of the cadaver until the autopsy, dry-ice was used for 24 h below the cadaver’s neck. Prior to autopsy, postmortem CT was used to monitor the internal change and to record the pre-autopsy condition. The same CT protocol was used as case 1. Free air was detected in the cranium, and brain parenchyma had shrunk, shifting to the posterior side. The brain parenchyma showed different densities, with a gradient and the area of transition was seen at the pons (Fig. 2a). Both cerebellar lobes were off the lower scale at the brain window view setting but its structure was detected at the lung window setting (Fig. 2b). The autopsy revealed deteriorated cerebral parenchyma, but the pons and cerebellum parenchyma had been maintained (Fig. 2c). After cutting the pons and cerebellum parenchyma, the
4. Experimental evaluation to verify lower CT density in brain
5. Discussion Postmortem CT has been reported as useful in detecting and evaluating bleeding lesion [9] and trauma [10], and postmortem CT looks promising in postmortem examination, as a good alternative for a refused autopsy or a good adjunct to autopsy [10]. Using
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M. Sugimoto et al. / Legal Medicine 18 (2016) 62–65
Fig. 2. A 60-year-old male found at his room; (a) postmortem brain CT (WL 35, WW 80), (b) postmortem brain CT (WL-600, WW 1500), and (c) macroscopic brain photography (view from the top). (a) The brain parenchyma shows different densities with a gradient and the area of transition is seen at the pons. The dorsal pons presents 13.9 ± 6.1 HU and the ventral pons presents 39.1 ± 5.9 HU. Both cerebellar lobes are off the lower scale at the brain window view setting, but its construction is detected at the lung window setting (b). (c) The pons and cerebellum have kept their shape and can be evaluated by cutting. The cerebral lobes are deteriorated after opening of the cranium.
Fig. 3. An extracted pig brain freezing on dry-ice; (a) postmortem brain CT (WL 40, WW 80) as a control image (0 min freezing), (b) 50 min freezing, and (c) macroscopic brain photography after 18 h freezing. The brain parenchyma shows different densities with a gradient, and the area of transition is seen at the dry-iced side (b). The brain tissue has decreased its density from 72.6 ± 1.4 HU to 6.5 ± 1.5 HU. (c) The cut surface presented like sherbet, macroscopically.
M. Sugimoto et al. / Legal Medicine 18 (2016) 62–65
autopsy confirmation, abnormal high density lesion on postmortem CT was reported as intracranial bleeding [11,12], pericardial cavity containing blood [13,14], and aortic rupture [13,15], and low density lesion as inclusion of extra-anatomical air [16– 18]. These findings were diagnosed based on the clinical CT image findings. In our presented cases, there was lower density (compared with normal tissue) in postmortem brain CT, so that the differential diagnosis might be interpreted as an edematous change due to infarction [19,20], fatty tissue containing lesion [21,22], or air migration into the brain/cranium [23]. An autopsy recognized the sherbet brain parenchyma at the lower density parenchyma. This is the first report that frozen tissue presented lower density on postmortem CT. The molecular structure of ice shows a continuous well-ordered four-surface structure, and consequently there is empty space between the water molecules [24,25]. CT density is calculated based on the X-ray absorption coefficient, and the CT density shows in proportion to the material’s density, unrelated to the material’s condition [26]. The density of ice is lower than that of liquid water, so that its X-ray absorption coefficient is 0.92 compared to liquid water [26,27]. Therefore, the ice density was – 80 HU in theory [26,27]. If solid ice was present in the frozen cadaver, its CT value is – 80 HU in theory, but the sherbet tissue showed a relatively higher CT value than solid ice (and lower CT value than normal organ) in our cases. The averaged CT value might reflect a mixture of frozen with non-frozen tissue. O’Donnell et al. [28] reported the appearance of ice crystals in liver and spleen on PMCT. According to their report, the frozen effect influenced the liver and spleen, and the tissue contained the ice crystals on postmortem CT. In our cases, there is no crystalized density in liver or spleen parenchyma. We speculated that the tissue containing a ratio of fat/water may affect the extent of freezing, and ice crystals might present with further cooling [27]. The distance from dry ice also affected the formation of ice crystals. If the body temperature was monitored during the dry-ice procedure, the correlation between the change of CT value and temperature might be apparent. In practice, the freezing procedure (using dry ice) is commonly used to prevent the worm-eaten deterioration of the cadaver. Therefore, the cadaver’s postmortem condition (with or without freezing effect) should be evaluated to enable the correct image interpretation on postmortem CT. In our case, even after advanced putrefaction, the sherbet brain tissue kept its shape, so that it could be evaluated after ex vivo investigation. If a suitable freezing technique can be employed when the cadaver demonstrates putrefaction, the organ investigation (at least brain parenchyma evaluation) might become easier, and detailed investigation would be possible using the technique. Further study will be needed in order to use the frozen technique in forensic investigation. In conclusion, frozen tissue can exhibit a lower density than non-frozen tissue, and this is confirmed by autopsy. When interpreting postmortem CT images, background information is crucial for precise diagnosis. Moreover, regardless of the unknown postmortem CT findings, it is necessary to take the proper precautions when making a diagnosis. Acknowledgment We thank Prof. Dr. Myles O’Brien (Mie Prefectural College of Nursing, Tsu, Mie, Japan) for assistance with English Language. References [1] C. O’Donnell, N. Woodford, Post-mortem radiology – a new sub-speciality?, Clin Radiol. 63 (2008) 1189–1194.
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[2] H. Hyodoh, S. Watanabe, R. Katada, K. Hyodoh, H. Matsumoto, Postmortem computed tomography lung findings in fatal of hypothermia, Forensic Sci. Int. 231 (2013) 190–194. [3] H. Hyodoh, J. Shimizu, S. Watanabe, S. Okazaki, K. Mizuo, H. Inoue, Timerelated course of pleural space fluid collection and pulmonary aeration on postmortem computed tomography (PMCT), Leg. Med. 17 (2015) 221–225. [4] M.J. Thali, K. Yen, W. Schweitzer, P. Vock, C. Boesch, C. Ozdoba, et al., Virtopsy, a new imaging horizon in forensic pathology: virtual autopsy by postmortem multislice computed tomography (MSCT) and magnetic resonance imaging (MRI) – a feasibility study, J. Forensic Sci. 48 (2003) 386–403. [5] S.G. Ross, M.J. Thali, S. Bolliger, T. Germerott, T.D. Ruder, P.M. Flach, Sudden death after chest pain: feasibility of virtual autopsy with postmortem CT angiography and biopsy, Radiology 264 (2012) 250–259. [6] C. Pichereau, E. Maury, L. Monnier-Cholley, S. Bourcier, G. Lejour, M. Alves, et al., Post-mortem CT scan with contrast injection and chest compression to diagnose pulmonary embolism, Intensive Care Med. 41 (2015) 167–168. [7] A. Kanazawa, H. Hyodoh, S. Watanabe, M. Fukuda, M. Baba, S. Okazaki, et al., New pitfalls of high-density postmortem computed tomography, Leg. Med. 16 (2014) 297–299. [8] A. Christe, P. Flach, S. Ross, D. Spendlove, S. Bolliger, P. Vock, et al., Clinical radiology and postmortem imaging (Virtopsy) are not the same: specific and unspecific postmortem signs, Leg. Med. 12 (2010) 215–222. [9] S. Kasahara, Y. Makino, M. Hayakawa, D. Yajima, H. Ito, H. Iwase, Diagnosable and non-diagnosable causes of death by postmortem computed tomography: a review of 339 forensic cases, Leg. Med. 14 (2012) 239–245. [10] M. Scholing, T.P. Saltzherr, P.H. Fung Kon Jin, K.J. Ponsen, J.B. Reitsma, J.S. Lameris, et al., The value of postmortem computed tomography as an alternative for autopsy in trauma victims: a systematic review, Eur. Radiol. 19 (2009) 2333–2341. [11] M. Hayakawa, S. Yamamoto, H. Motani, D. Yajima, Y. Sato, H. Iwase, Does imaging technology overcome problems of conventional postmortem examination? A trial of computed tomography imaging for postmortem examination, Int. J. Legal Med. 120 (2006) 24–26. [12] H. Iwase, D. Yajima, M. Hayakawa, S. Yamamoto, H. Motani, A. Sakuma, et al., Evaluation of computed tomography as a screening test for death inquest, J. Forensic Sci. 55 (2010) 1509–1515. [13] M. Burke, S. Parsons, R. Bassed, Management of medicolegal natural deaths from hemopericardium or hemothorax using postmortem CT scanning, Forensic Sci. Med. Pathol. 8 (2012) 367–372. [14] S. Watanabe, H. Hyodoh, J. Shimizu, S. Okazaki, K. Mizuo, M. Rokukawa, Classification of hemopericardium on postmortem CT, Leg. Med. 17 (2015) 376–380. [15] S. Shiotani, M. Kohno, N. Ohashi, K. Yamazaki, H. Nakayama, K. Watanabe, et al., Non-traumatic postmortem computed tomographic (PMCT) findings of the lung, Forensic Sci. Int. 139 (2004) 39–48. [16] C. Jackowski, M. Sonnenschein, M.J. Thali, E. Aghayev, K. Yen, R. Dirnhofer, et al., Intrahepatic gas at postmortem computed tomography: forensic experience as a potential guide for in vivo trauma imaging, J. Trauma 62 (2007) 979–988. [17] S. Shiotani, Y. Ueno, S. Atake, M. Kohno, M. Suzuki, K. Kikuchi, et al., Nontraumatic postmortem computed tomographic demonstration of cerebral gas embolism following cardiopulmonary resuscitation, Jpn. J. Radiol. 28 (2010) 1–7. [18] M. Ishida, W. Gonoi, K. Hagiwara, Y. Takazawa, M. Akahane, M. Fukayama, et al., Intravascular gas distribution in the upper abdomen of non-traumatic in-hospital death cases on postmortem computed tomography, Leg. Med. 13 (2011) 174–179. [19] N. Takahashi, Y. Lee, D.Y. Tsai, K. Ishii, Development of an algorithm for the detection of early signs of cerebral ischemia on CT images, Nihon Hoshasen Gijutsu Gakkai Zasshi 63 (2007) 835–842. [20] H. Saito, S. Katsuragawa, T. Hirai, S. Kakeda, Y. Kourogi, A computerized method for detection of acute cerebral infarction on CT images, Nihon Hoshasen Gijutsu Gakkai Zasshi 66 (2010) 1169–1177. [21] G.M. Bydder, L. Kreel, R.W. Chapman, D. Harry, S. Sherlock, L. Bassan, Accuracy of computed tomography in diagnosis of fatty liver, Br. Med. J. 281 (1980) 1042. [22] B. Wang, Z. Gao, Q. Zou, L. Li, Quantitative diagnosis of fatty liver with dualenergy CT. An experimental study in rabbits, Acta Radiol. 44 (2003) 92–97. [23] Y. Uchiyama, S. Katsuragawa, H. Abe, J. Shiraishi, F. Li, Q. Li, et al., Quantitative computerized analysis of diffuse lung disease in high-resolution computed tomography, Med. Phys. 30 (2003) 2440–2454. [24] Y.T.K. Nomura, High School Chemistry II, Suken Shuppan Co. Ltd., 2010, p. 25. [25] N.S.K. Toshima, Understandable Chemistry I/II, Buneido, 2010, p. 294. [26] T. Kawamura, H. Fukushi, Observation of internal structure in sea ice by X-ray computed tomography, Low Temp. Sci. 45 (1986) 59–67. [27] H. Hyodoh, K. Ogura, M. Sugimoto, Y. Suzuki, A. Kanazawa, R. Murakami, et al., Frozen (iced) effect on postmortem CT – experimental evaluation, J. Forensic Radiol. Imaging 3 (2015) 210–213. [28] C. O’Donnell, P. Bedford, M. Burke, Massive hemoperitoneum due to ruptured ectopic gestation: postmortem CT findings in a deeply frozen deceased person, Leg. Med. 13 (2011) 245–249.
Contents lists available at ScienceDirect
Legal Medicine journal homepage: www.elsevier.com/locate/legalmed
Case Report
Freezing effect on brain density in postmortem CT Miyu Sugimoto, Hideki Hyodoh ⇑, Masumi Rokukawa, Ayumi Kanazawa, Rina Murakami, Junya Shimizu, Shunichiro Okazaki, Keisuke Mizuo, Satoshi Watanabe Department of Legal Medicine, Sapporo Medical University, S1 W17 Chuo-ku, Sapporo 060-8556, Japan
a r t i c l e
i n f o
Article history: Received 15 November 2015 Received in revised form 16 December 2015 Accepted 17 December 2015 Available online 18 December 2015 Keywords: Postmortem CT Freezing effect Postmortem change Forensic radiology Low density
a b s t r a c t Two 60-year-old males were found at their homes whose bodies had deteriorated due to putrefaction. To prevent worm invasion and minimize deterioration, dry ice was used prior to the autopsy investigation. Prior to autopsy, postmortem CT demonstrated a decreased density in brain parenchyma at the dry-iced side, and autopsy revealed deteriorated brain parenchyma with frozen effect (presented like sherbet). Moreover, the deteriorated cerebral parenchyma maintained their structure and they were evaluated by cutting. When lower CT density presents in postmortem CT, the freezing effect may need to be considered and the physician should evaluate the cadaver’s postmortem condition to prevent misdiagnoses. Ó 2015 Elsevier Ireland Ltd. All rights reserved.
1. Introduction
2. Case 1
One of the recent topics of interest in legal medicine is postmortem CT, and many postmortem CT studies have been reported prior to postmortem investigation and/or full-autopsy examination [1–3]. Thali et al. [4] reported the usefulness of postmortem computed tomography (CT) to evaluate the cadaver objectively and with surface scan technique; they named it ‘‘Virtopsy”. The usefulness of postmortem CT has been reported, and in recent years, postmortem CT angiography has also been reported, and identified the causes of death in certain cases [5,6]. However, in situations when knowledge regarding postmortem image changes and the background of the cadaver is lacking, the precise interpretation of postmortem CT is difficult and it might result in incorrect conclusion [7]. Even if a CT image contains specific findings which seem to point to a clear conclusion, if the physician does not have knowledge of postmortem change, the apparent conclusion may be incorrect [7,8]. In this report, we present our finding of a lower density region on postmortem brain CT, which proved to be the effect of frozen tissue on autopsy examination. We investigate its mechanism and report this new pitfall in postmortem CT investigation. To verify the lower CT density in brain, we examined an additional ex vivo experiment.
A 60-year-old male (165.0 cm, 29.2 kg) was found dead in his room. The cadaver was lying on the bed without any extrinsic injury. Before the scheduled autopsy (2 days later), the cadaver was surrounded by dry ice to prevent worm invasion and minimize deterioration. Prior to autopsy, postmortem CT was used to monitor the internal change and to record the pre-autopsy condition. Postmortem whole body CT was performed using a 64-slice multi-detector CT scanner (Aquilion CX, Toshiba, Tochigi, Japan). Neck to head; 120 kV, 300 mA, 1.0 s/rotation, pitch factor 0.641, configuration 0.5 32, reconstruction 0.5 mm, MPR (multi-planar reformation) image reconstruction: 5 mm in the axial sections. Neck to foot; 120 kV, 50–400 mA (variable mA), 0.5 s/rotation, pitch factor 0.828, configuration 0.5 32, MPR (multi-planar reformation) image reconstruction: 7 mm in the axial sections. On postmortem CT, free air was detected in the cranium, and different densities were detected in the deteriorated brain parenchyma (19.4 ± 5.4 HU and 40.9 ± 4.4 HU), which appeared to exhibit decreased brain parenchymal density at the dry-iced side (Fig. 1a). An autopsy revealed deterioration in the brain parenchyma on the right side, but less deterioration on the left side (Fig. 1b). After cutting the parenchyma, the left-side cerebral parenchyma was frozen and presented like sherbet. No hematoma or infarction was detected in the brain autopsy. The postmortem CT also presented pneumothorax in the left pleural cavity, and its volume was 4.2 L (Fig. 1c). The mediastinum was shifted to the right side, which might be the cause of the
⇑ Corresponding author. E-mail address: [email protected] (H. Hyodoh). http://dx.doi.org/10.1016/j.legalmed.2015.12.007 1344-6223/Ó 2015 Elsevier Ireland Ltd. All rights reserved.
M. Sugimoto et al. / Legal Medicine 18 (2016) 62–65
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Fig. 1. A 60-year-old male found in his room; (a) postmortem brain CT, (b) macroscopic brain photography (view from the top), and (c) postmortem chest CT. (a) Intracranial and intravascular air density is demonstrated due to putrefaction. The shifted brain parenchyma shows layered densities; 19.4 ± 5.4 HU at the left side, and 40.9 ± 4.4 HU at the right side. (b) The right-side brain parenchyma deteriorated, but the left-side brain parenchyma kept its shape. The left-side brain parenchyma can be evaluated by cutting and it seems sherbet-like parenchyma. (c) Large free-air density (4.2 L) in the left pleural cavity, right-side shifted mediastinum, and right pleural space fluid collection (420 mL) is demonstrated. An autopsy proves no other causes of death, and tension pneumothorax is thought to be the cause of death.
respiratory and circulatory dysfunction. An autopsy revealed convex deformation of the left diaphragm to the abdominal cavity, left lung contraction, and right-sided mediastinum deviation. Consequently, the cause of death was diagnosed as respiratory and circulatory dysfunction due to the left tension pneumothorax.
tissue was frozen and the parenchyma presented like sherbet. No hematoma or infarction was revealed in the brain autopsy. Consequently, the cause of death was designated as unknown.
3. Case 2
This ex-vivo study was not needed to approve our institutional animal ethics committee. Commercially available extracted pig brain tissue (Hokkaido Wako Pure Chemical Industries, Ltd. Sapporo) was put into a sealed bag and placed on the dry-ice. The tissue was placed in the CT room (20 °C) through the whole observation period, and the whole tissue was examined by CT. Before and after freezing, a CT examination was performed in the same scanner using the following protocol: 120 kV, 200 mA, 0.5 s/rotation, pitch factor 0.641, configuration 0.5 32, reconstruction 0.5 mm. The pig brain parenchyma showed lower density after freezing (Fig. 3a and b). Comparing the CT numbers before and after freezing, the brain tissue has decreased its density from 72.6 ± 1.4 HU to 6.5 ± 1.5 HU. The cut surface presented like sherbet, macroscopically (Fig. 3c).
A 60-year-old male (167.7 cm, 51.8 kg) was found dead in his room. Because a stench had been noticed, a police investigator was requested to gain admittance to his room, and found the cadaver lying on the bed without any extrinsic injury. There were many worms in the cadaver. For personal identification and to investigate the cause of death, an autopsy was scheduled. To minimize deterioration and worm invasion of the cadaver until the autopsy, dry-ice was used for 24 h below the cadaver’s neck. Prior to autopsy, postmortem CT was used to monitor the internal change and to record the pre-autopsy condition. The same CT protocol was used as case 1. Free air was detected in the cranium, and brain parenchyma had shrunk, shifting to the posterior side. The brain parenchyma showed different densities, with a gradient and the area of transition was seen at the pons (Fig. 2a). Both cerebellar lobes were off the lower scale at the brain window view setting but its structure was detected at the lung window setting (Fig. 2b). The autopsy revealed deteriorated cerebral parenchyma, but the pons and cerebellum parenchyma had been maintained (Fig. 2c). After cutting the pons and cerebellum parenchyma, the
4. Experimental evaluation to verify lower CT density in brain
5. Discussion Postmortem CT has been reported as useful in detecting and evaluating bleeding lesion [9] and trauma [10], and postmortem CT looks promising in postmortem examination, as a good alternative for a refused autopsy or a good adjunct to autopsy [10]. Using
64
M. Sugimoto et al. / Legal Medicine 18 (2016) 62–65
Fig. 2. A 60-year-old male found at his room; (a) postmortem brain CT (WL 35, WW 80), (b) postmortem brain CT (WL-600, WW 1500), and (c) macroscopic brain photography (view from the top). (a) The brain parenchyma shows different densities with a gradient and the area of transition is seen at the pons. The dorsal pons presents 13.9 ± 6.1 HU and the ventral pons presents 39.1 ± 5.9 HU. Both cerebellar lobes are off the lower scale at the brain window view setting, but its construction is detected at the lung window setting (b). (c) The pons and cerebellum have kept their shape and can be evaluated by cutting. The cerebral lobes are deteriorated after opening of the cranium.
Fig. 3. An extracted pig brain freezing on dry-ice; (a) postmortem brain CT (WL 40, WW 80) as a control image (0 min freezing), (b) 50 min freezing, and (c) macroscopic brain photography after 18 h freezing. The brain parenchyma shows different densities with a gradient, and the area of transition is seen at the dry-iced side (b). The brain tissue has decreased its density from 72.6 ± 1.4 HU to 6.5 ± 1.5 HU. (c) The cut surface presented like sherbet, macroscopically.
M. Sugimoto et al. / Legal Medicine 18 (2016) 62–65
autopsy confirmation, abnormal high density lesion on postmortem CT was reported as intracranial bleeding [11,12], pericardial cavity containing blood [13,14], and aortic rupture [13,15], and low density lesion as inclusion of extra-anatomical air [16– 18]. These findings were diagnosed based on the clinical CT image findings. In our presented cases, there was lower density (compared with normal tissue) in postmortem brain CT, so that the differential diagnosis might be interpreted as an edematous change due to infarction [19,20], fatty tissue containing lesion [21,22], or air migration into the brain/cranium [23]. An autopsy recognized the sherbet brain parenchyma at the lower density parenchyma. This is the first report that frozen tissue presented lower density on postmortem CT. The molecular structure of ice shows a continuous well-ordered four-surface structure, and consequently there is empty space between the water molecules [24,25]. CT density is calculated based on the X-ray absorption coefficient, and the CT density shows in proportion to the material’s density, unrelated to the material’s condition [26]. The density of ice is lower than that of liquid water, so that its X-ray absorption coefficient is 0.92 compared to liquid water [26,27]. Therefore, the ice density was – 80 HU in theory [26,27]. If solid ice was present in the frozen cadaver, its CT value is – 80 HU in theory, but the sherbet tissue showed a relatively higher CT value than solid ice (and lower CT value than normal organ) in our cases. The averaged CT value might reflect a mixture of frozen with non-frozen tissue. O’Donnell et al. [28] reported the appearance of ice crystals in liver and spleen on PMCT. According to their report, the frozen effect influenced the liver and spleen, and the tissue contained the ice crystals on postmortem CT. In our cases, there is no crystalized density in liver or spleen parenchyma. We speculated that the tissue containing a ratio of fat/water may affect the extent of freezing, and ice crystals might present with further cooling [27]. The distance from dry ice also affected the formation of ice crystals. If the body temperature was monitored during the dry-ice procedure, the correlation between the change of CT value and temperature might be apparent. In practice, the freezing procedure (using dry ice) is commonly used to prevent the worm-eaten deterioration of the cadaver. Therefore, the cadaver’s postmortem condition (with or without freezing effect) should be evaluated to enable the correct image interpretation on postmortem CT. In our case, even after advanced putrefaction, the sherbet brain tissue kept its shape, so that it could be evaluated after ex vivo investigation. If a suitable freezing technique can be employed when the cadaver demonstrates putrefaction, the organ investigation (at least brain parenchyma evaluation) might become easier, and detailed investigation would be possible using the technique. Further study will be needed in order to use the frozen technique in forensic investigation. In conclusion, frozen tissue can exhibit a lower density than non-frozen tissue, and this is confirmed by autopsy. When interpreting postmortem CT images, background information is crucial for precise diagnosis. Moreover, regardless of the unknown postmortem CT findings, it is necessary to take the proper precautions when making a diagnosis. Acknowledgment We thank Prof. Dr. Myles O’Brien (Mie Prefectural College of Nursing, Tsu, Mie, Japan) for assistance with English Language. References [1] C. O’Donnell, N. Woodford, Post-mortem radiology – a new sub-speciality?, Clin Radiol. 63 (2008) 1189–1194.
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