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Journal of the Anatomical Society of India

The Branching Pattern of Internal Thoracic Artery On The Anterior Chest Wall

Author(s): Gupta, M., Sodhi, L., Sahni, D.

Vol. 51, No. 2 (2002-07 - 2002-12)

Department of Anatomy, Postgraduate Institute of Medical Education and Research, Chandigarh, INDIA

Abstract

The branches of internal thoracic artery (ITA) are well documented in the textbooks of Anatomy. However, during the routine dissections of anterior thoracic wall variations in these branches from their usual description were observed. The present study was conducted to study the branching pattern of ITA, which is the main source of blood supply to the sternum.

Thirty formalin fixed specimens of ITA, obtained from adult cadavers were studied. Length of ITA, level of its termination and distribution of its branches were observed. The mean length of ITA was same on both sides (158 mm). It was rectilinear in its course but in 1/3rd of the cases, it was observed to have a medial concavity. Trifurcation of ITA was seen only in 8.3% specimens where the 3rd branch supplied the diaphragm, while the bifurcation was seen in 91.7%. The overall mean distance of right and left ITA from sternal margins was 8.28 ± 2.13 mm and 8.26 ± 2.39 mm respectively. Corforming to the usual description, the ITA was observed to give sternal, anterior intercostal (AIC) and perforating branches. Besides these, the sternal branches were found to be arising from intercostal or perforating branches through a common stem. Usually, two AIC braches arise from the ITA and supply the respective intercostal space. Whereas, in the present study besides these the AIC arteries arose by a common stem with sternal branches and with AIC branches of same space or adjacent space. The AIC arteries were absent in upper three spaces in a few specimens and the intercostal space was supplied by a continuation of posterior intercostal artery.

These branches of ITA and presence of posterior intercostal artery in the anterior part of intercostal space result in a continued blood supply to anterior thoracic wall after mobilization of ITA.

Key words: Sternal, anterior intercostal, perforating, arteries, internal thoracic artery.

Introduction:

IInternal thoracic artery (ITA) is often mobilized for coronary artery bypass grafting. It is the main source of blood supply to the sternum and any damage to this supply results in sternal wound complications. (Hazelrigg et al 1989; Loop et al, 1990; Carrier et al. 1992).

The ITA usually gives pericardiophrenic, mediastinal, pericardial, sternal, anterior intercostal, perforating, and terminal branches as described in various textbooks of Anatomy (Williams et al. 1995, Romanes, 1996; McMinn, 1994 and Snell, 2000). The surgical anatomy of the ITA has been described by Henriquez et al. (1997). However, during the routine dissections of anterior thoracic wall, variations of ITA branches from this description were observed. Hence the present study was undertaken to observe these variations in the branching pattern of ITA in the thorax.

Materials And Methods:

The present study was conducted on 30 specimens of anterior thoracic wall obtained from adult cadavers, in the department of Anatomy, Postgraduate Institute of Medical Education and Research, Chandigarh. The anterior thoracic wall was removed consisting of full length of sternum alongwith 1st to 7th costal cartilages of both sides. The specimens were then fixed in formalin and the ITA was carefully dissected.

The length, course in the thorax and level of termination of ITA per hemisternum were recorded. The distance between the ITA and sternal margins in each space per hemisternum was measured. The branches of both ITA from 1st to 6th intercostal (IC) space were dissected and traced. Only sternal, anterior intercostal and perforating branches were dissected and studied The incidence & distribution of these branches were noted. The mean length, mean distance from sternal margins per space, incidence of various courses of ITA and incidence of level of termination of ITA, were calculated. The range and mean number of various branches of ITA were also calculated statistically.

Observations and Results:

The ITA was present bilaterally in all the specimens of the present study. The mean length of ITA in the thorax was same on both sides (Right 158.0 mm 2.6 mm, Left 158.0 1.3 mm). Its course was rectilinear in majority of cases (Table 1). The commonest level of bifurcation of right ITA was 6th rib (43.3%) and of left ITA was 6th IC space (33.4%) (Table 2). The trifurcation (Fig. 1) of ITA was observed in 10% on right side and 6.7% on left side, where the third branch was found to be supplying the diaphragm. The distance between ITA and the sternal margins was greatest at the 2nd IC space on both sides. The overall mean distance being 8.28 2.13 mm on the right and 8.26 2.39 mm on the left side (Table 3).

The branches of each ITA, their incidence, range and mean number are shown in Table 4, and are described below :

Table 1 : Incidence of courses of ITA per hemisternum A. Sternal branches were either arisinig directly from ITA or from other branches of ITA.

Course of ITA Right Left
n % n %
1. Rectilinear 20 66.7 19 63.3
2. Curved        
( a) Medial concavity 10 33.3 11 36.7
(b) Lateral concavity - - - -
3. Tortous - - - -

A. Sternal branches were either arisinig directly from ITA or from other branches of ITA.

  1. A range of 5-9 sternal branches on the right side and 4-9 on the left were arising directly from ITA and supplying the sternum.
  2. A range of 0-2 sternal branches on the right and 0-3 on the left were also supplying the respective intercostal spaces besides the sternum. They were arising through a common stem with anterior intercostal arteries and divided in a T shaped manner to supply both the areas (Fig. 2a).
  3. A range of 0-4 sternal branches on the right and 0-3 on the left side were found to be arising by a common stem with the perforating branches (Fig. 2b).

B. Anterior intercostal (AIC) branches :

A range of 6-12 AIC branches on the right and 5- 10 on the left side were supplying the IC spaces. These branches were absent in upper three spaces in a few specimens.

Table II : Incidence of level of termination of ITA per hemisternum

Level Right Left
Bifurcation Trifurcation Bifurcation Trifurcation
n % n % n % n %
5 rib 1 3.3 - - - - - -
5 IC space 2 6.7 - - 6 20.0 1 3.3
6 rib 13 43.3* 2 6.7 8 26.6* - -
6 IC space 10 33.4* - - 10 33.4* - -
7 rib - - 1 3.3 2 6.7 - -
7 IC space 1 3.3 - - 2 6.7 1 3.3
Total 27*** 90.0 3** 10 28*** 93.3 2** 6.7

n - number of specimens
% - percentage
Note: The commonest level of termination of right (76.7%)* and left* (60%)* ITA was 6th rib or 6th IC space.

The total number of trifurcations of both ITA, was 8.3%** and total bifurcations were 91.7%***.

Table III : Mean distance between ITA and sternal margins in each IC space per hemisternum

Intercostal
space
Right Left
Mean (mm) SD (±) Mean (mm) SD (±)
1 7.73 3.96 7.90 3.53
2 9.60 2.89 9.56 2.99
3 8.83 2.03 8.86 3.09
4 7.93 2.79 6.90 2.92
5 6.86 2.51 5.13 2.14
6 5.26 2.65 3.53 1.99
Overall 8.28 2.13 8.26 2.39

Table IV: Distribution range and mean number of branches of ITA per hemisternum

  Right Left
Branches of ITA Incidence Range Mean No SD(±) Incidence Range Mean No SD(±)
(A) Sternal
(i) Sternal branches 100% 5-9 06.90 (1.30) 100% 4-9 06.06 (1.96)
(ii) A branch dividing into Y or T shaped manner into sternal and intercostal branch 80% 0-2 01.10 (0.71) 83% 0-3 01.30 (0.87)
(iii) A branch dividing into sternal and perforating branch 73.3% 0-4 01.46 (1.22) 60% 0-3 01.16 (1.08)
(B) Anterior intercostal branches 100% 6-12 09.80 (1.24) 100% 5-10 08.38 (0.23)
(i) Two AIC arteries arising from each ITA in each I.C. Space 90% 2-5 01.56 (1.24) 80% 2-4 01.18 (1.06)
(ii) AIC artery arising by a Common stem with sternal branch 80% 0-2 01.10 (0.71) 83% 0-3 01.30 (0.87)
(iii) AIC arteries dividing into two and supplying same IC space 60% 0-3 01.32 (0.86) 70% 0-3 01.87 (1.03)
(iv) AIC dividing into two on the rib and supplying adjacent space 40% 0-1 01.12 (0.72) 30% 0-1 00.86 (1.32)
(v) AIC artery absent instead PIC artery present 70% 0-2 01.10 (0.75) 70% 0-3 01.13 (0.93)
(C) Perforating 100% 0-4 03.01 (0.23) 100% 0-4 03.11 (1.21)
  1. Two AIC arteries were arising (Fig. 3a) in 2-5 IC spaces on the right and 2-4 IC spaces on the left.
  2. The AIC artery was arising by a common stem with sternal branches (Fig. 2a) as described in sternal branches (0-2 right, 0-3 left).
  3. The AIC artery was arising from ITA and dividing into two branches to supply the same IC space (Fig. 3b) (0-3 on both sides).
  4. The AIC artery was arising from ITA against the rib and supplied the adjacent spaces (Fig. 3b) (0-1 on both sides).
  5. The AIC arteries of some IC spaces were absent, instead the anterior part of IC space was supplied by a continuation of posterior intercostal (PIC) artery (Fig. 4) (0-2 right, 0-3 left).

C. Perforating branches

A range of 0-4 perforating branches on both sides were found to pierce the IC space near the lateral margin of the sternum and were found to enter the pectoralis major muscle.

Discussion:

The ITA was not found to be absent in any specimen in the present study as also observed in the series studied by Arnold (1972) and Henriquez et al. (1997). The mean length of ITA on both sides in the present study was found to be 158 mm. In the study by Henriquez et al. (1997) its mean length was 204 mm. However, the lengths of ITA of these two studies are not comparable since the present study gave the length of ITA in the thorax while the latter gave the total length of ITA. The course of ITA apart from being mostly rectilinear showed a medial concavity in 33.3% on the right and 36.7% on the left side and no case of lateral concavity or tortuosity was seen. Henriquez et al. (1997) reported rectilinear course in 34%, medial concavity in 30%, lateral concavity in 29% and tortuosity in 7% cases.

In the present study the commonest level of termination of right ITA (76.7%) and left ITA (60.0%) was on the 6th rib or 6th IC space as described in various textbooks of Anatomy. In rest of the specimens, ITA terminated from 5th rib to 7th intercostal space as also reported by Arnold (1972). It was observed to be bifucating in 90% cases on the right and 93.3% on the left, the incidence being almost similar to that reported by Henriquez at al. (1997). The ITA of both sides was trifurcating in 8.3% specimens while it trifurcated in 7% cases in the study by Henriquez et al. (1997). The distance from sternal margin was maximum at 2nd IC space in present study while it was a little lower as observed by Henriquez et al. (1997).

The ITA is usually described to give sternal, anterior intercostal & perforating branches besides others (Arnold, 1972, Williams et al. 1995, Romanes, 1996). Sternal branches were arising directly from ITA as usually described by earlier workers and in textbooks of Anatomy. Besides these, in the present study sternal branches were also seen arising by a common stem with AIC and perforating arteries. (Gupta et al, 2002)

Most of the anterior part of IC spaces was supplied by two AIC arteries as usually described. In some IC spaces, there was only one AIC artery arising from ITA and it divided into two, supplying the same space or adjacent space where it was arising against the rib. In a few IC spaces the AIC artery was arising by a common stem with sternal branches as discussed above. Green (1991) in his operative findings, described more frequent presence of common origin of sternal and intercostal branches as compared to present study.

In a few spaces where the ITA was not giving any AIC branches, the space was supplied by the continuation of PIC artery. The presence of these collateral branches from the PIC artery was also described by De Jesus and Acland (1995) but they did not mention about variations of the anterior intercostal arteries.

Carrier at al. (1992) reported that after sternotomy and bilateral grafting of ITA the decrease in blood supply to the sternum is only transient and is completely reverted one month after the operation. Green (1991) has also stated that important collateral blood vessels can provide a continued blood supply to the sternum even after bilateral mobilization of ITA.

Summary & Conclusion

The ITA was not found to be absent in any specimen in the present study. The mean length of ITA was found to be 158 mm. The course of ITA apart from being mostly rectilinear showed a medial concavity in 33.3% on the right and 36.7% on the left side and no case of lateral concavity or tortuosity was seen.

The commonest level of termination of right ITA (76.7%) and left ITA (60.0%) was on the 6th rib or 6th IC space. Bifurcation was seen in 90% cases on the right and 93.3% on the left. The ITA of both sides was trifurcating in 8.3% specimens. The distance of ITA from the sternal margin was maximum at 2nd IC space.

Sternal branches were arising directly from ITA and were also arising by a common stem with AIC and perforating arteries. Most of the anterior part of IC spaces was supplied by two AIC arteries. In some IC spaces, there was only one AIC artery arising from ITA and it divided into two, supplying the same space or adjacent space. The IC space was supplied by the continuation of PIC artery.

References:

  1. Arnold, M. (1972) : The surgical anatomy of sternal blood supply. Journal of Thoracic and Cardiovascular Surgery 64: 596-610.
  2. Carrier, M., Gregoire, J., Tronc, F et al. (1992) : Effect of internal mammary artery dissection on sternal vascularisation. Annals of Thoracic Surgery 53: 115-119.
  3. De Jesus, R.A., Acland, R.D. (1995) : Anatomic study of the collateral blood supply of the sternum. Annals of Thoracic Surgery 59: 163-168.
  4. Green, G.E. Sternotomy incision, mobilization and routing of ITA grafts. In: Green GE, Singh RN, Sosa JA (eds) Surgical Revascularization of the heart: the internal thoracic arteries. Igaku-shion Medical Publisher. New York. pp 119-127.(1991)
  5. Gupta, M; Sodhi, L; Sahni, D. (2002) : Variations in collateral contributions to the blood supply to the sternum. Surgical Radiological Anatomy 24: 265-70.
  6. Hazelrigg, S.R., Wellons, H.A., Schneider, J.A. et al. (1989): Wound complications after median sternotomy. Journal of Thoracic and Cardiovascular Surgery 98: 1096-1099.
  7. Henriquez-Pino, J.A., Gomes, W.J., Prates, J.C., Buffoto, E. (1997): Surgical Anatomy of the internal thoracic artery. Annals of Thoracic Surgery 64: 1041-1045.
  8. Loop, F.D., Lytle, B.W., Cosgrove, D.M. et al. (1990): Sternal wound complications after isolated coronary artery bypass grafting: early and late mortality, morbidity and cost of care. Annals of Thoracic Surgery 49: 179-187.
  9. McMinn, R.M.H. Last's Anatomy, Regional and applied. In: Thorax McMinn RMH editor. 9th ed. Churchill Livingstone. Edinburgh. p 248. (1994).
  10. Romanes, G.J. Cunningham's Manual of Practical Anatomy Thorax and Abdomen. In : The wall of the thorax. Romanes GJ (edr) 15th ed. Vol.2. University Press Oxford. p 15. (1996).
  11. Snell R.S. Clinical Anatomy for medical students. The Thorax Part I. In: The thoracic wall Snell, R.S. Edr. 6th ed. Lippincott Williams and Wilkins. Philadelphia: p 51. (2000).
  12. Willaims P.L. Bannister L.H. Berry M.M. et al.: Gray's Anatomy. The anatomical basis of medicine and surgery. In Cardiovascular. System Giorgia Gabellar (edr.) 38th edn. Churchill Livingstone Edinburgh: p 1534. (1995).

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Fig. 1. A dissection of posterior surface of anterior thoracic wall showing left internal thoracic artery (LITA) bifurcating (b) in 6th IC space and right internal thoracic artery (RITA) trifurcating (t) in 6th IC space.

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Fig. 2a: A dissection of posterior surface of anterior thoracic wall showing a common branch (B) originating from LITA, dividing in T shaped manner into sternal (S) and AIC branches. Note the common branch (B) also giving a branch to supply the adjacent IC space.

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Fig. 2b: A dissection of posterior surface of anterior thoracic wall showing the RITA, giving a common branch (B) which divides into sternal (S) and perforating branch (P).

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Fig 3a: A dissection of posterior surface of anterior thoracic wall showing the LITA giving two AIC arteries in the 5th IC space.

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Fig. 3b: A dissection of posterior surface of anterior thoracic wall showing one AIC artery arising from the LITA and dividing into two to supply the same space and one AIC artery arising from RITA and dividing into two branches to supply the adjacent IC space.

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Fig. 4 A dissection of posterior surface of anterior thoracic wall showing that anterior part of 3rd intercostal space is supplied by continuation of posterior intercostal (PIC) artery. The LITA gave no AIC branches in this space.

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