An application of a quantitative analytical system for the grading of pulmonary fat embolisms

Forensic Scrience Znternutional, 39 (19881 Elsevier Scientific Publishers Ireland Ltd.

263

AN APPLICATION OF A QUANTITATIVE ANALYTICAL FOR THIE GRADING OF PULMONARY FAT EMBOLISMS

SYSTEM

YASUO BUNAI*, NAOKI YOSHIMI, HIDEOU KOMORIYA, MINE0 IWASA and ISA0 OHYA Deportmenr:s of Legal Medicine and Pathology, (Japad

Gifu Univetsity

School of Medicine, Gij% 500

(Received January 4th, 19881 (Revision received April 18th, 19881 (Accepted April 18th. 19881

The severity of pulmonary fat embolism in 5 autopsied cases has been measured using a quantitative image analytical system. With reference to the mean size of the fat emboli. the cases were divided into 2 groupings regardless of the number of the emboli. The mean sizes of the emboli lin 3 cases of the first group were significantly larger (about 499-666 ~‘1 than those found in the 2 cases of the other group (about 220 and 235 @l. An investigation into the localization of fat emboli revealed that more were lodging in the small arteries and artelioles in the first group than in the second. Our results have indicated that a reliable grading of pulmonary fat embolism can not be established without a quantitative image analysis of the size and localization of th.e fat emboli, and that this quantitative analytical method is useful in achieving this reliable grading. Key words: Pulmonary fat embolism: Quantitative image analysis

Introduction Ever since the first description of a fat embolism by Zenker, the lesion has been intensively studied [l - 51. Though the genesis and pathophysiology of the lesion are still under discussion, it has been widely accepted that a severe pulmonary fat embolism frequently becomes fatal in a patient with a fracture. Some investigators have attempted to establish the criteria to evaluate the severity of histologically detected pulmonary fat embolisms in order to determine its contribution to the cause of death, and have classified them into degrees or gradings, such as mild, moderate and severe, in semiquantitative ways [5-81. Even so, it is not rare for considerable difficulties to arise :in deciding whether the embolism could have played a prime role in the death of a victim. A problem in reaching a decision is that these gradings are not essentially objective but subjective. Thus, a reliable quantitative analytical method is needed to determine the severity of pulmonary fat embolism. *To whom correspondence should be addressed. 0379-0738/881$03.50

0 1988 Ekevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland

264

Recent advances in medical electronics have seen the development of quantitative image analytical methods which help pathologists to make morphometric diagnoses in their histopathologic and cytopathologic studies. In this paper, we discuss an application of a quantitative analytical method for measuring the severity of a pulmonary fat embolism, so as to clarify its significance in the medicolegal field. Materials and Methods Five autopsied cases were studied, showing moderate or gross pulmonary fat embolism according to the grading by Sevitt [5]. All were victims of traffic accidents and had been found to have sustained bone fractures. In each case, 5 tissue samples were obtained from the formalin-fixed lungs; one piece from each lobus. All tissues were immersed overnight in a 0.5% 0~0, solution and then rinsed in running water. Next, the tissues were cut by a cryostat into 8 pm thicknesses.

Fig. 1. (a) Fat emboli in the pulmonary vessels. A frozen section cut from the lung tissue postfixed with osmium tetraoxide, x 266. (Case 4). 01) Computer graphic display of the same position.

Fig. 2. Definition of a size of the embolus.

Image analysis was performed by the Rapid Image Sensor Analytical System (RISAS) which uses charge coupled devices (NEC Co., Tokyo, Japan), and developed at the First Department of Pathology, Gifu University School of Medicine, Gifu, Japan [9]. This system can distinguish the fat emboli, which stain black from the OsO,, from the surrounding tissue, because of the higher density of fat emboli (Fig. 1). whose sizes then can be calculated by a YD 8110 computer (Yedata Co., Tokyo, Japan), (Fig. 2). If anthracotic granules or formalin pigments are present, however, this system can not distinguish the emboli, since these granules or pigments have a similar density. Thus in this study, fat emboli smaller than 50 pm2 were not studied. In spite of this condition, more than 90% of the fat emboli could be measured, and most granules and pigments could be avoided. In each case, the total measured area was 2-3 cm2. Suspected content of embolic fat of the lung was calculated by the following equation. SC = :N x M x Lv x lo6 (cm31 SC, Suispected content of embolic fat of the lung (cm% N, Number of embolic fat per mm2; M, Mean size of embolic fat (pm2); Lv, Volume of the lung (cm% Results Table 1 summarizes the number, mean size, and suspected contents of the

266 TABLE

1

QUANTITATIVE

ANALYSIS

OF FE* USING RISAS

Case

Sex

Age

No. of FE per mm*

Mean size of FE IpnY

Suspected content of Fe of the lung km4

1 2 3 4 5

M M F M M

17 6 53 79 56

2.92 3.42 7.60 48.85 89.40

510.63 603.68 236.08 491.81 219.86

1.69 0.93 1.26 23.99 16.70

*Fat emboli **Significantly

f 681.11** f 858.53** zt 312.30 * 2,049.37*+ zt 496.41

different from caees 3 and 5 (P < 0.001).

embolic fat in the lung. The number of fat emboli increased corresponding to the grading of the fat embolism. In regard to the mean size, however, the cases were divided into 2 groups, regardless of the grading. The mean sizes of cases 1,2 and 4 were found to be significantly larger than those of cases 3 and 5 P < 0.0011. The investigation of the distribution of the emboli revealed that the former group showed more emboli lodging in the small arteries and arterioles than the latter group (Table 21. In the image analytical examination, fat emboli lodging in the capillaries were smaller than 1000 pm” in size, whereas those in the small arteries and arterioles were larger than 500 m2. The largest fat embolus found in case 4 was about 75,000 w2 in size. Discussion A fat embolism is a well-known clinical entity divisible into 2 groups: embolisms with complicating clinical symptoms and embolisms with no cliniTABLE

2

DISTRIBUTION

1 2 3 4 5 *Percentage

OF SIZE OF FE

-500

~1000

-5000

~10,000

10,0001 nJ

65.4* 63.6 88.3 80.5 92.6

21.0 21.4 9.0 10.5 4.6

13.1 14.5 2.7 7.7 2.7

0.5 0.5 0 0.7 0.1

0 0 0 0.6 < 0.1

of size of each FE.

267

Fig. 3. (a) Small arteries completely obstructed by fat emboli. (Case 4). (b) Numerous small fat emboli observed in the pulmonary capillaries. (Case 5). Frosen sections cut from the lung tissue post-fixed w itb osmium tetraoxide, x 75.

cal symptoms [2]. The former is referred to as fat embolism syndrome, which occurs in 0.5% -2Ob of long bone fractures and approaches a 5Ob- 10% incidence in multiple fractures associated with pelvic injuries, and primarily manifests severe respiratory insufficiency with coagulation abnormalities. The latter is considered fat embolisation as a subclinical event, its occurrence associated with almost all long bone fractures, other traumatic and nontraumatic conditions. This latter embolization is usually a postmorten finding rather than a clinical syndrome [2]. In the :medicolegal field, fat embolism also is important as a cause of death as well as for revealing evidence of antemorten violence. There still remains an unsettled problem: how to determine the significance of a fat embolism found on autopsy. Some investigators have classified the severity of the pulmonary fat embolism and have attempted to link this to the cause of death [5--81, claiming that some victims showing the most severe grade of

268

pulmonary fat embolism may have died because of the embolism. In contrast, other investigators often have difficulty in deciding whether a pulmonary fat embolism really was the cause of death. One problem in reaching a decision over the scope of the role that a fat embolism may play, is that gradings for the severity of the embolism are not essentially objective; they are gradings that are mainly based on the number and form of the emboli. Whiteley [lo] and Moore et al. [ll] have shown that embolic blockage in the small arteries and arterioles has caused more severe complications than similar or larger amounts of embolic fat lodging in the alveolar capillaries. In this present study, the mean sizes of the emboli in cases 1, 2 and 4 were significantly larger than those in cases 3 and 5. Moreover, the former group showed more emboli lodging in the small arteries or arterioles than did the latter group (Fig. 2). In a histological examination and quantitative analysis of the fat contents of the lungs by chloroform extraction, Brinkmann et al. [l] have revealed that the histological degree of a pulmonary fat embolism is equivalent to an occlusion of half of all vessels in corpses with a total fat content of about 20 g or more, and that this content presented proof of death caused by a fat embolism in corpses which show no conflicting diseases or organic damages. If the grading of a fat embolism was determined based only on the number of emboli, the most severe case in the present study is case 5, whose suspected content of fat in the lung was 16.7 cm5. Yet, though the number of fat emboli found in case 4 was about half that of case 5, the suspected content of fat of case 4 was 23.99 cm3, which exceeded that of case 5 and satisfies the criteria advocated by Brinkmann et al. These results suggest that the size and localization of fat emboli differ from case to case, and that a quantitative grading of fat embolism can not be established, regardless of these parameters. A reliable grading of the fat embolism, based on an optical examination, is only capable of being done by experienced observers. The grading needs an analysis of its many parameters, such as the number, size and localization of the emboli. Quantitative image analysis in this present study has made it possible to measure some of these parameters with objectivity and reproducibility. This quantitative method has proven very useful to both experienced and nonexperienced observers and has aided in making reliable gradings of pulmonary fat embolism. Acknowledgement This work was supported in part by a Grant-in-Aid (62770401) from the Ministry of Education, Science and Culture, Japan. References 1

B. Brinkmann, M. Bornger and M. Biilow, Die Fettembolie der Lungen als Todesursache, Atiologie, Pathogenese und Beweisfiihrung. Z. Rechtsmed, 78 (1976) 255- 272.

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H.R. Gossling and V.D. Pellegrini, Fat embolism syndrome, A review of the pathophysiology and physiological basis of treatment. Cl& O&q., 166 (1982) 68-82. 3 L.F. Peltier, Fat embolism, A current concept. Cl& O&hop., 66 (1969) 241-253. 4 L.F. Peltier, Fat embolism, An appraisal of the problem. CZin Crthop., 187 (1984) 3- 17. 5 S. Sevitt. Fat Embolism, Butterworth, London, 1962. 6 H.E. Emson, Fat embolism studied in 100 patients dying after injury. J. Cl% Pathol, 11 (1968) :!8 - 35. 7 G. F&d, R. Henn und W. Spann, tiher pulmonale Fettembolie nach Traumen mit verschieden langer ijherlebenszeit. M&CA. iUed Wsdr., 106 (1964) 978 - 981. 8 A.H.T. BobbSmith, Pulmonary fat-embolism. Lancet, I(19411 135- 141. 9 A. Nislhikawa,H. Nishikawa and M. Takahashi, Development of analytical cytology system using charge coupled devices (CCD) and fundamental study of cell image analysis. Acta Sch. Med. Univ. Gifu, 32 (1984) 108- 130. 10 H.J. Whiteley, The relation between tissue injury and the manifestations of pulmonary fat embolism. J. PathoL Bad, 67 (1964) 521- 530. 11 D.B. Moore, R.J. Graff, S. Lang and MD. Pareira, Studies on the mechanism of death in pulmonary microembolism. Surg. GynecoL Obstet, 107 (1958) 615-622. 2