The sternalis muscle variation is a well-known anatomical situation. It is present
in 8.7% of women and 6.4% of men, although the incidence varies according
to sex, race and ethnicity. During a left modified radical mastectomy operation
on a 46-year-old female patient a sternalis muscle was detected on the pectoralis
major muscle in the superficial fascia. It was in craniocaudal position and
was parallel to the body of the sternum. The cylindrical muscle was approximately
8 cm in length and 2 cm in diameter. Such variations are considered to
have their origin in embryological development. Awareness of muscular variations
and their identification is important both for procedure through the proper
dissection planes during breast surgery and in radiological examination and
follow-up

B, Kabay

B, Ozdemir

E, Adiguzel

I, Akdogan

English

Via Medica Journals

Folia Morphol. Vol. 64, No. 4, pp. 338–340Copyright © 2005 Via MedicaISSN 0015–5659www.fm.viamedica.plC A S E   R E P O R T338Address for correspondence: Bülent Özdemir, MD, PhD, Pamukkale Unv. Tip Fakultesi, Anatomi Anabilim Dali, 20020, Denizli, Turkey,tel: +90 258 213 40 30, fax: +90 258 213 28 74, e-mail: bulento@hacettepe.edu.tr; mehmeto@Pamukkale.edu.trThe left sternalis muscle variation detectedduring mastectomyBurhan Kabay1, Ilgaz Akdogan2, Bulent Ozdemir2, Esat Adiguzel21Pamukkale University Faculty of Medicine, Department of General Surgery, Denizli, Turkey2Pamukkale University Faculty of Medicine, Department of Anatomy, Denizli, Turkey[Received 27 September 2005; Accepted 27 October 2005]The sternalis muscle variation is a well-known anatomical situation. It is presentin 8.7% of women and 6.4% of men, although the incidence varies accordingto sex, race and ethnicity. During a left modified radical mastectomy operationon a 46-year-old female patient a sternalis muscle was detected on the pecto-ralis major muscle in the superficial fascia. It was in craniocaudal position andwas parallel to the body of the sternum. The cylindrical muscle was approxi-mately 8 cm in length and 2 cm in diameter. Such variations are considered tohave their origin in embryological development. Awareness of muscular varia-tions and their identification is important both for procedure through the properdissection planes during breast surgery and in radiological examination andfollow-up.Key words: sternalis muscle, thorax, breast, mastectomy, variationINTRODUCTIONThe sternalis muscle is a well-known anatomicalvariation [7]. It is located at the anterior wall of thethorax in the parasternal region [1]. According toTurner, it was named by Cabrolio in 1604 [1] and in1926 the features of the muscle were described byDupuy [1, 7].Incidence of the muscle varies according to sex,race and ethnicity [1]. It is more common amongwomen (8.7%) than among men (6.4%) [10]. It ispresent among white races in 2.9–6.4%, whileamong black races it is present in 11% [6]. Ethnicbackground is also important in view of the distri-bution of the sternalis muscle in certain populationgroups; the incidence is 4–8% in Indians [5], 13.1%in Japanese, 3.3% in Filipinos and 1% Chinese [6]. Itis usually unilateral [2]. Anatomists use a number ofdifferent terms to refer to the sternalis muscle, suchas the “parasternal”, “pectoris rectus” or “praester-nalis” muscle [1].Even though, as has been remarked, the sterna-lis muscle variation is well known in the literature,information about it is inadequate with the excep-tion that supplied by a few anatomy books [7]. It isdefined as a muscle that begins from the lower partof the ribs and the rectus sheath and then coursesupward, finally inserting the upper part of the ster-num and ribs or the sternocleidomastoid [3]. Thepositioning of the sternalis muscle adjacent to thebreast is of clinical importance.CASE REPORTDuring a left modified radical mastectomy opera-tion on a 46-year-old female patient for stage III inva-sive ductal carcinoma a left sternalis muscle was en-countered after dissection of the skin flaps. The mus-cle was located anterior to the thorax and was detect-ed between the superficial and deep sheath of the su-perficial fascia on the pectoralis major muscle and fas-cia parallel to the sternum in craniocaudal position.339Burhan Kabay et al., The left sternalis muscle variation detected during mastectomyIt lay between the 3rd rib and 6-7th rib cartilage lateral tothe insertion of the pectoralis major muscle (Figs. 1, 2).The sternalis muscle was removed with the breast andwas found to be a cylindrical muscle of approximately8 cm in length and 2 cm in diameter. The muscle tissuewas verified in histological examination.Figure 1. Photograph showing the sternalis muscle during the modified radical mastectomy opera-tion; sm — sternalis muscle.Figure 2. The diagram showing the position of the sternalis muscle; sm — sternalis muscle; pmm — pec-toralis major muscle; 2, 3, 4, 5, 6 — ribs 2, 3, 4, 5 and 6 (computer modified using the figures in the NetterHuman Anatomy Atlas and the Sobotta Human Atlas).340Folia Morphol., 2005, Vol. 64, No. 4DISCUSSIONWe report here the case of a sternalis muscleencountered during a left modified radical mastec-tomy and removed en bloc with the specimen. Themuscle was removed because of its close proximity(although without macroscopic invasion) to the tu-moral mass and the positioning of a thick layer ofbreast tissue under the muscle. Leaving this musclein its place might have been detrimental to the on-cological surgery of the breast. Firstly, the pectoralfascia and the entire breast tissue must be includedin the specimen during modified radical mastecto-my. Secondly, muscle tissue in close proximity to thetumoral mass may harbour tumoral nests within lym-phatics penetrating the muscle. For dissection of thepectoral fascia and the breast tissue to be completeand to ensure that no tumour tissue is left in place,this muscle was included in the specimen. The deci-sion to remove the muscle or not may be affectedby its localisation, direct invasion with the tumourand the presence of breast tissue under the muscle.Removal of the muscle did not cause any functionalor cosmetic loss and it was easy to dissect with thepectoral fascia under it.Most skeletal muscle is derived from the myo-tome regions of the somites. Some head and neckmuscles are derived from branchial or pharyngealarch mesoderm. The limb muscles develop in situfrom somatic mesoderm. Cardiac muscle and mostsmooth muscle is derived from splanchnic meso-derm. The sternalis appeared to be a continuationof the rectus abdominis muscle. However, it mightbe derived from a primitive ventral longitudinalmuscle sheet which gives rise to the pectoralis, ster-nocleidomastoid, rectus abdominis and ventrolater-al part of the diaphragm [9]. The sternalis is proba-bly derived from the pectoral muscle group [7]. Turn-er suggests that the sternalis could be an upwardprolongation of the rectus abdominis or a down-ward extension of the sternocleidomastoid. It is prob-ably a vestigial remnant of muscle lost during evolu-tion that is expressed in some individuals [5].The origin and nerve supply of the sternalis musclehave, therefore, puzzled anatomists. Most authors,however, hold the view that it is derived from the pec-toralis major muscle. Kida et al. [7] worked on 40 casesover 15 years and discovered that the sternalis muscleis supplied by the pectoralis nerves. Branches of theintercostal nerves may pierce the muscle to becomecutaneous but do not directly supply the sternalis. Noattempt was made in our study to demonstrate mus-cle innervation and vascularisation. The function of themuscle is uncertain [5], although anomalies of the ster-nalis in association with abnormalities of the pectora-lis major have been described [7, 8].There is a need to record and discuss unusualanatomical variants with the use of complex diag-nostic and therapeutic tools as these variants couldpresent a challenge to the radiologist or surgeon inmaking a diagnosis. The sternalis muscle can be eas-ily overlooked during breast surgery and may oftencause a diagnostic dilemma on mammography orCT scans. In mammography the sternalis muscle canmimic a malignant breast mass [4]. Surgeons andradiologists must therefore be familiar with it andits location and orientation must be known in orderto decide whether to remove the muscle or not. Inour view the removal of this muscle helps completedissection of the breast tissue and pectoral fascia,especially for tumours located in the inner upper andlower quadrants. We advise that the muscle be re-moved for this type of tumour. In the event of pre-operative confusion, a CT scan or MR imaging canaid in establishing the diagnosis.A recent case report indicates that many surgeonsare not familiar with the sternalis muscle [2]. How-ever, awareness of the muscle and its early identifi-cation are necessary in order to proceed in an ap-propriate plane during surgical dissection. This casereport puts forth the importance of the sternalismuscle for surgeons and radiologists.REFERENCES1. Arraez-Aybar LA, Sobrado-Perez J, Merida-velasco JR(2003) Left musculus sternalis. Clin Anat, 16: 350–354.2. Bailey PM, Tzarnas CD (1999) The sternalis muscle: a nor-mal finding encountered during breast surgery. PlastReconstr Surg, 103: 1189–1190.3. Bannister LH, Berry M, Collins P, Dyson M, Dussek JE,Ferguson MWJ (1995) Gray’s anatomy, 38th ed.Churchill Livingstone, Edingburg, p. 838.4. Bradley FM, Hoover HC Jr, Hulka CA, Whitman GJ,McCarthy KA, Hall DA, Moore R, Kopans DB (1996)The sternalis muscle: an unusual normal finding seenon mammography. Am J Roentgenol, 166: 33–36.5. Harish K, Gopinath KS (2003) Sternalis muscle: importancein surgery of the breast. Surg Radiol Anat, 25: 311–314.6. Jeng H, Su SJ (1998) The sternalis muscle: an uncommonanatomical variant among Taiwanese. J Anat, 193: 287–288.7. Kida MY, Izumi A, Tanaka S (2000) Sternalis muscle:topic for debate. Clin Anat, 13: 138–140.8. O’Neill MN, Folan-Curran J (1998) Case report: bilater-al sternalis muscles with a bilateral pectoralis majoranomaly. J Anat, 193: 289–292.9. Sadler TW (2004) Langman’s medical embrylogy, 9th ed.Lippincott Williams and Wilkins, Baltimore, pp. 199–209.10. Scott-Conner CEH, Al-Jurf AS (2002) The sternalis mus-cle. Clin Anat, 15: 67–69.

The left sternalis muscle variation detected during mastectomy

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The left sternalis muscle variation detected during mastectomy

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