Abstract
OBJECTIVE The aim of the study was to explore the anatomy of the intercostobrachial nerve in rats.
METHODS Dissections of 8 Sprague-dawley rats were performed to examine the intercostobrachial nerve. Fifteen dissections were successful. The position of the nerve, origin, termination, length and diameter were measured and recorded.
RESULTS 1) 80% of the nerves originated from the second intercostal space and 20% from the first intercostal space; 2) 60% of the nerves terminated in the latissimus dorsi and 40% in the axillary skin 3) the branches of the nerves only were divided into 2 types, single and double; 4) the length of the nerves ranged from 2.4 to 3.4 cm with an average of 2.97±0.90 cm; 5) the diameter of the nerves was thicker at their origin compared to their termination.
CONCLUSION The intercostobrachial nerve is simple in rats with 60% terminating in the latissimus dorsi.
keywords
Breast cancer is one of the most common malignancies in women. The vast majority of patients presenting with breast cancer will undergo surgical resection, usually combined with an axillary lymph node dissection (ALND)[1,2]. With increasing morbidity associated with ALND, intercostobrachial nerve (ICBN) preservation is of more concern to achieve better quality of life.[3,4]
Rat anatomy is relatively similar to that of the human. The rat is a favored laboratory animal and is commonly used in research because it is inexpensive, reliable and easily available. [5,6] Studies of the anatomy of the ICBN are essential prior to starting a large scale clinical study in patients. The objectives of this study were to become familiar with the anatomical details of the area involved, improve skills and develop techniques to examine the ICBN. This research will provide us with practical information for future clinical study.
Materials and Methods
Eight female Sprague-Dawley (SD) rats, weighting from 405~486 g and a length of 29~36 cm, were obtained from the Experimental Animal Center of Tianjin Medical University. The rats were kept under standard laboratory conditions (room temperature 22 ±0.5°C, 12 h light-dark cycle, 60% humidity and standard rat chow and water ad libitum). Experiments were approved by the Committee for Animal Research (CAR) of the Tianjin Medical University. All efforts were made to minimize the number of animals and their suffering.
The rats were anaesthetized by an intraperitoneal injection of 10% chloral hydrate at a dose of 400 mg/kg body weight.[7] Using normal surgical procedures a single incision was made from the middle line of the sternum, up to the jugular notch and down to 1 cm above the costal arch. After exposure of the perctoralis, the ICBN was found along the outer edge of the perctoralis minor. The ICBN was separated toward its origin and termination. The point of its origin and termination, length, diameter and variation of the nerves were measured and recorded. An axillary dissection was performed with the isolation of the ICBN being successful in 15 of the 16 cases attempted.
The statistical analysis-was conducted using SPSS 12.0 software. Data were presented as the mean±SD.
RESULTS
The origin and termination of the ICBN
The ICBN originated from the first intercostal space in 3 out of the 15 cases (20%), and from the second intercostal space in 12 cases (80%). In 4 cases (26.7%) the nerves terminated at the latissimus dorsi, in 6 cases (40%) at the axillary skin and in 5 cases (33.5%) at both the latissimus dorsi and axillary skin (Table 1).
The origin and termination of the intercosto-brachial nerve in 15 dissections in SD rats
The branches of the ICBN
There were 10 cases (66.7%) with a single branch (Fig.1) and 5 cases (33.3%) with 2 branches (Fig.2).
Single branch of the intercostobrachial nerve in a SD rat.
Double branches of the intercostobrachial nerve in a SD rat.
The diameter of the ICBN
The diameter of ICBN at its origin averaged 0.51 ±0.09 mm and at its termination 0.48+0.10 mm. The nerve was thicker at the origin than in the end, but there was no significant difference.
The length of the ICBN
The average length of the ICBN was 2.97 ±0.29 cm. The distance from the nerve to the middle point of the clavicle, the border line of the sternum, the bottom edge of axillary vein and the bottom of the axilla are shown in Table 2.
The diameter, length and relative position of the intercostobrachial nerve
DISCUSSION
Although the surgical anatomy of the axilla has been described, the path of the ICBN encountered by the surgeon during axillary dissection is highly variable. The benefits of preserving the ICBN during axillary dissection for breast cancer have been reported in several descriptive studies.[3,8,9] Therefore, it is necessary and important to understand the detailed anatomy of this structure in animals so that better surgical skills can be achieved. A description of the anatomy of therat ICBN is also of value.
The anatomy of rat ICBN has not been described in the literature. In our anatomical study of 8 rats (15 cases) we found the following: 1) the origin of the ICBN in rats is stable with 80% originating from the second intercostal space and 20% from the first intercostal space; 2) the termination of the nerve is also stable in that 40% of the nerves terminated at the axillary skin and 60% reached the latissimus dorsi or both the latissimus dorsi and axillary skin. Whether this nerve functions as a motor neuron requires further study, which is undergoing in our laboratory; 3) the diameter of the nerve is slightly thicker at its origin compared to its termination, but there is no significant difference between them; 4) the branches of the nerve is simply described as there are only 2 variations with single or double branches; and 5) the distribution of the nerve supplying the axilla and upper arm is also stable as we found that it is parallel to the axillary vein, vertical to the long thoracic nerve and extends to the axilla.
The anatomy of the ICBN in man was constant in some dissections,[10] whereas it was highly variable in another report.[11] The anatomy of ICBN in rat is simple. One reason may be that in rats there is less individual variability. A second reason maybe that the rats used in our study were healthy and the dissections of the axilla were performed under normal conditions. It is possible that variations may be numerous during a disease process.
- Received November 9, 2005.
- Accepted January 10, 2006.
- Copyright © 2006 by Tianjin Medical University Cancer Institute & Hospital and Springer
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