The sternalis muscle in the Bulgarian population: classification of sternales

An unusual sternalis with variation of the contralateral sternocleidomastoid muscle: a case report

PURPOSE

To report a previously undocumented variant of sternalis.

METHODS

An unusual muscle was observed during routine dissection.

RESULTS

The sternalis muscle located in the right thoracic region originated from the superior portion of the rectus abdominis sheath and 5-6th costal cartilages, crossed the midline and attached at the sternum. The muscle fibers then ascended with the left sternocleidomastoid muscle as an additional fasciculus, of which the superior ends were finally terminated at the left mastoid process. The sternalis muscle of the thoracic region was innervated by the anterior cutaneous branches of right intercostal nerve, while the additional fasciculus ascended with the left sternocleidomastoid muscle was innervated by the branches of left accessory nerve.

CONCLUSIONS

This study presents a unilateral sternalis muscle with the contralateral sternocleidomastoid variation. It will enhance the exhaustive classification of sternalis, and provide significant information to radiologists, angiologists and surgeons for better interpretation of images and safer interventions.

Anatomical variants identified on chest computed tomography of 1000+ COVID-19 patients from an open-access dataset

Chest computed tomography (CT) has been the preferred imaging modality during the pandemic owing to its sensitivity in detecting COVID‐19 infections. Recently, a large number of COVID‐19 imaging datasets have been deposited in public databases, leading to rapid advances in COVID‐19 research. However, the application of these datasets beyond COVID‐19‐related research has been little explored. The authors believe that they could be used in anatomical research to elucidate the link between anatomy and disease and to study disease‐related alterations to normal anatomy. Therefore, the present study was designed to investigate the prevalence of six well‐known anatomical variants in the thorax using open‐access CT images obtained from over 1000 Iranian COVID‐19 patients aged between 6 and 89 years (60.9% male and 39.1% female). In brief, we found that the azygos lobe, tracheal bronchus, and cardiac bronchus were present in 0.8%, 0.2%, and 0% of the patients, respectively. Variations of the sternum, including sternal foramen, episternal ossicles, and sternalis muscle, were observed in 9.6%, 2.9%, and 1.5%, respectively. We believe anatomists could benefit from using open‐access datasets as raw materials for research because these datasets are freely accessible and are abundant, though further research is needed to evaluate the uses of other datasets from different body regions and imaging modalities. Radiologists should also be aware of these common anatomical variants when examining lung CTs, especially since the use of this imaging modality has increased during the pandemic.

Variations in the anterior thoracic wall with sternalis muscle and accessory pectoralis major muscle

PURPOSE

The new type of the sternalis muscle needs to be recognized, and the accessory pectoralis major muscle (AcPM) was found between the pectoralis major and minor muscle. It needs to be acknowledged those two different variations can exist in one case.

METHODS

The muscle was found on a 73-year-old male cadaver during the dissection class for the anterior thoracic wall. It was proceeded to identify the adjacent structures with precise dissection.

RESULTS

The cadaver had sternalis muscle bilaterally. Both side sternalis muscles had a medial and lateral belly and attached to pectoral fascia and rectus abdominis sheath. The pectoralis major muscle (PMaj) had a more profound slip attached to the costal cartilage of rib 4 and 5, which is AcPM. The pectoral nerve traveled through the clavipectoral fascia to the AcPM and through PMaj to the sternalis muscle.

CONCLUSIONS

This study presented a new type of sternalis muscle. Two different variations were developed along with the pectoral nerve. It needs to be recognized in the diagnostic images, the muscle rehab outcome, and the surgical complication.

Digastric musculus sternalis

PURPOSE

To report a rare variant muscle.

METHODS

Aberrant muscle was observed in the anterior chest wall musculature during routine cadaver prosection.

RESULTS

Musculus sternalis consisting of two muscular bellies united at an angle by an intermediate tendon was observed anterior to the pectoral major of the left side. The muscle did not have any bony attachment.

CONCLUSIONS

The present case represents a hybrid muscle with superior belly derived from the prepectoral mass and inferior belly from ventral longitudinal muscle column. Clinically, the musculus sternalis may be misinterpreted as a pathological mass or lesion thus its accurate knowledge is significant to radiologists, angiologists and surgeons for better interpretation of mammographic images, safer interventions and for reconstructive surgeries.

The prevalence and distribution of sternalis muscle: a meta-analysis of published literature of the last two hundred years

The sternalis muscle (SM) is an anatomical variant that lies subcutaneously and is superficial to the pectoralis major muscle or sternum. The present meta-analysis was conducted to analyze the prevalence, anatomical features, and variance of the SM in different population. In total, 98 studies were included for this meta-analysis. Eighty-two studies dealt with adult subjects, and sixteen studies with fetuses. The worldwide prevalence of SM was observed to be 6% or 0.06 [0.05-0.7, 95% CI] in 27,470 adults, whereas it was 0.29 [0.20-0.39, 95% CI] in 673 fetuses. In 259 anencephalic fetuses, the prevalence was 44% or 0.44 [0.26-0.63, 95% CI], while the same in 414 fetuses without anencephaly was 16% or 0.16 [0.06-0.27, 95% CI]. The reported prevalence rate in Asian mongoloid population (9.1% = 0.091) was three times that of the Asian Caucasian population (3.33% = 0.0333). The prevalence in European descent was 3.93%. Interestingly, the reported prevalence rates in North and South American populations were 3.44% and 3.66%, almost being equivalent. The cadaveric investigations revealed that the SM had an overall prevalence of 5.96% in adults based on 76 studies, which was higher than other modalities of investigations. The multi-detector computerized tomography (MDCT) had shown the prevalence of approximately 4.33%. The same was reported in surgical studies and mammographic studies as 0.47% and 0.02%, respectively. The SM is not an unusual variant of the chest wall musculature. MDCT could be a new method to precisely demonstrate the morphology, course, and size of the SM in vivo.

Sternalis muscle in jordanian population: a prevalence study and level of physicians' awareness

Sternalis muscle (SM) is an anatomical variant that lies parallel to the sternum. It is present in (8%) of human population. Awareness about its presence during thoracic imaging is important, since it might be misdiagnosed as a tumor. This study is the first that discusses the prevalence of SM in the Jordanian population and document the level of awareness about SM among intern doctors and surgery and radiology residents. Our aims are to know the prevalence of SM in the Jordanian population, using thoracic multi-detector computerized tomography (CT) images, and to assess the awareness about SM among a sample of intern and resident Jordanian physicians. Random anonymous axial thoracic multi-detector CT images of 1,709 (801 females and 908 males) Jordanian patients, were examined for the presence or absence of unilateral and/or bilateral SM. A questionnaire aiming to identify SM was distributed among 175 intern doctors, 26 surgery resident and 28 radiology resident doctors, their answers were summarized. The prevalence of SM among Jordanians is 5.9%. The prevalence of unilateral SM is 2.1% on the right side of the thorax and 1.9% on the left side, bilateral prevalence was 1.8%. While 35.7% of the radiology residents could identify SM using CT and/or anatomy images, only 3.9% of surgery residents and none of the intern doctors could. We concluded that SM is present in the Jordanian population, with a prevalence of 5.9% which falls within the global average. Intern doctors and surgery and radiology residents are almost unaware and unfamiliar about SM.

Exploring Anatomic Variants to Enhance Anatomy Teaching: Musculus Sternalis

The opportunity to encounter and appreciate the range of human variation in anatomic structures—and its potential impact on related structures, function, and treatment—is one of the chief benefits of cadaveric dissection for students in clinical preprofessional programs. The dissection lab is also where students can examine unusual anatomic variants that may not be included in their textbooks, lab manuals, or other course materials. For students specializing in physical medicine, awareness and understanding of muscle variants has a practical relevance to their preparations for clinical practice. In a routine dissection of the superficial chest muscles, graduate students in a human gross anatomy class exposed a large, well-developed sternalis muscle. The exposure of this muscle generated many student questions about M sternalis: its prevalence and appearance, its function, its development, and its evolutionary roots. Students used an inquiry protocol to guide their searches through relevant literature to gather this information. Instructors developed a decision tree to assist students in their inquiries, both by helping them to make analytic inferences and by highlighting areas of interest needing further investigation. Answering these questions enriches the understanding and promotes “habits of mind” for exploring musculoskeletal anatomy beyond simple descriptions of function and structure.

Prevalence of the sternalis muscle in a sample of routinely dissected human cadavers

PURPOSE

Sternalis muscle is an uncommon muscle head attaching between the sternoclavicular joint superiorly and the costal cartilage near the xiphoid process.

METHODS

In this study, 36 cadavers (18 male, 18 female) were obtained through the Anatomical Board of the State of Florida and complete, routine musculoskeletal dissection was performed while adhering to all relevant laws and practices.

RESULTS

Two examples of the sternalis muscle belly (5%) were identified, one in a black male and one a white female. The sternalis muscles were bilateral in both cases and each was formed of a single muscle belly. The superior attachments were continuous with the sternal attachment of sternocleidomastoid, and the inferior attachments connected to the costal cartilages. Sternalis did not cross the midline and the T2-T5 anterior intercostal neurovasculature associated closely with the muscle belly. In the female, a well-formed unilateral chondrocoracoideus muscle was apparent with a branch from the medial pectoral nerve closely associated on the deep surface. No other abnormalities in the chest, axilla, or brachial plexus were noted on either cadaver, and the pectoralis major and minor muscles were normally formed and innervated in both cases.

CONCLUSION

This study supports other evidence in the literature that indicates the sternalis muscle has an average prevalence in the population of approximately 5%, and it appears across race and sex. Education about this structure is important for radiologists, surgeons, and doctors of physical therapy that may be involved in treatment and post-surgical rehabilitation of this region.

Describing the sternalis muscle: a new variant and an amended classification

PURPOSE

With emphasis on the clinical setting, knowledge of anatomical variation decreases misdiagnoses and surgical complications. We report a previously undocumented variant of sternalis muscle and recommend an augmented classification scheme.

METHODS

Dissection of the anterior thoracic wall on an 83-year-old female cadaver revealed bilateral sternalis muscles. The Snosek et al. classification system was referenced to describe the variant types.

RESULTS

The right sternalis muscle has a single belly and can be classified using the Snosek et al. classification system as a simple type, right single. The left sternalis muscle presented with three muscle bellies, each having a unique pattern of superior attachments (heads). This variation is previously undocumented and requires a more detailed classification.

CONCLUSIONS

We propose the addition of a new subtype of sternalis classification, as well as a modification to the Snosek et al. (Clin Anat 27:866-884, 2014) classification scheme, to include classification of different muscle bellies when multiple are present.

Evidence of the sternalis muscle in two South African cadavers

The sternalis muscle is an infrequent, non-pathological anatomical variant typically misrepresented in a clinical context. It presents with 3-8% prevalence, according to cadaveric studies. The muscles were identified during routine cadaver prosection at the School of Anatomical Sciences, University of the Witwatersrand. Here, we report two cases of the sternalis muscle in two South African White cadavers. Analysis of the sternalis muscles revealed unilaterally present, distinctly defined muscle masses on the right (case number 1, female) and left (case number 2, male) hemithorax, lateral to the sternum. The muscles occurred with a prevalence of 2.25% within the cadaveric population examined. The prevalence of the sternalis muscle is generally low, especially in the European population. Their presence represents the remnants of the cutaneous muscles in the ventral thorax of lower animals. Clinically, the sternalis muscle may be misinterpreted as a pathological mass or lesion, thus accurate knowledge regarding its variations and prevalence is of importance.

Improvement in Existing Chest Wall Irregularities During Breast Reconstruction

Mastectomies for both cancer resection and risk reduction are becoming more common. Existing chest wall irregularities are found in these women presenting for breast reconstruction after mastectomy and can pose reconstructive challenges. Women who desired breast reconstruction after mastectomy were evaluated preoperatively for existing chest wall irregularities. Case reports were selected to highlight common irregularities and methods for improving cosmetic outcome concurrently with breast reconstruction procedures. Muscular anomalies, pectus excavatum, scoliosis, polythelia case reports are discussed. Relevant data from the literature are presented. Chest wall irregularities are occasionally encountered in women who request breast reconstruction. Correction of these deformities is possible and safe during breast reconstruction and can lead to improved cosmetic outcome and patient satisfaction.

Evolution of the muscular system in tetrapod limbs

While skeletal evolution has been extensively studied, the evolution of limb muscles and brachial plexus has received less attention. In this review, we focus on the tempo and mode of evolution of forelimb muscles in the vertebrate history, and on the developmental mechanisms that have affected the evolution of their morphology. Tetrapod limb muscles develop from diffuse migrating cells derived from dermomyotomes, and the limb-innervating nerves lose their segmental patterns to form the brachial plexus distally. Despite such seemingly disorganized developmental processes, limb muscle homology has been highly conserved in tetrapod evolution, with the apparent exception of the mammalian diaphragm. The limb mesenchyme of lateral plate mesoderm likely plays a pivotal role in the subdivision of the myogenic cell population into individual muscles through the formation of interstitial muscle connective tissues. Interactions with tendons and motoneuron axons are involved in the early and late phases of limb muscle morphogenesis, respectively. The mechanism underlying the recurrent generation of limb muscle homology likely resides in these developmental processes, which should be studied from an evolutionary perspective in the future.

A previously unclassified variant of sternalis muscle

PURPOSE

We propose an addition to the Snosek et al. classification to include a subtype variant of sternalis muscle: mixed type and triple subtype.

METHODS

Dissection of the anterior thorax of a 96-year-old female cadaver revealed bilateral sternalis muscles with an undocumented variant of the right sternalis muscle.

RESULTS

The left sternalis muscle presented as a simple type-left single using the Snosek et al. classification scheme. The right sternalis muscle revealed a previously undocumented classification type. It consisted of three bellies and two heads, with the lateral head formed by two converging bellies and the medial head formed from the superficial medial belly.

CONCLUSIONS

The unique presentation of right sternalis muscle can be classified by expanding the Snosek et al. classification scheme to include triple-bellied subtypes. This presentation is classified as a mixed type-right triple, with single bicipital converging and single bicipital diverging. Documentation of sternalis muscle variations can prevent misdiagnoses within the anterior thorax.

Two Cases of Rectus Sternalis Muscle

The sternalis muscle, an uncommon anatomical variant of the chest wall musculature, though perhaps well known to anatomists, is quite unfamiliar to clinicians and radiologists despite attempts to highlight its clinical importance in recent years. During routine dissection for undergraduate medical teaching, in the department of anatomy, we came across two cases of sternalis muscle. The first was a unique case of unilateral right sternalis with contralateral insertion on the left sternocleidomastoid, and the second case where bilateral presence of the muscle was noted with ipsilateral insertion. The former was supplied by medial pectoral nerve and the latter by lower intercostal nerves. Usually present between the pectoral and superficial fasciae, wide ranging prevalence and morphology have been attributed to this muscular variant. Opinions differ on its development and nerve supply. Its presence can be misdiagnosed as a wide range of benign and malignant anterior chest wall lesions and tumours, but it is also of great use as a pedicle flap or flap microvascular anastomosis in reconstructive surgeries of anterior chest wall, head and neck and breast. In this paper, two cases of sternalis muscle which presented very differently from each other are discussed.

Sternalis Muscle: An Unexpected Finding during Mastectomy

Sternalis muscle also called rectus sternalis, rectus thoracis, or episternalis is an anomalous muscle of the anterior chest wall with unknown anatomical function. It is regularly observed in lower animal but infrequently in humans. Presence of this muscle can create confusion with tumours of the anterior chest wall during routine mammography. Although less is known about its origin and innervations, knowledge about this muscle can have many clinical implications. A case of unilateral sternalis muscle detected during mastectomy, in a female with carcinoma of the right breast, is being reported with a brief review of the literature and highlighting its clinical significance.

Sternalis muscle, what every anatomist and clinician should know

The sternalis muscle is a well documented but rare muscular variation of the anterior thoracic wall. It lies between the superficial fascia and the pectoral fascia and is found in about 8% of the population. It presents in several morphological variants both unilaterally and bilaterally and has no apparent physiological function. There is still much disagreement about its nerve supply and embryological origin. With the advent of medical imaging and thoracic surgery the clinical importance of this muscle has been re-emphasized. It has been implicated in misdiagnosis of breast masses on routine mammograms owing to its parasternal location and relative unfamiliarity among radiologists. When undetected before any thoracic surgery, it has the potential to interfere with and prolong such procedures. When present and detected preoperatively it can be used as a muscular flap in reconstructive surgeries of the breast and neck. This article will present the sternalis muscle with special emphasis on its morphology, homology, and clinical significance.

Prevalence and variance of the sternalis muscle: a study in the Chinese population using multi-detector CT

OBJECTIVE

To analyze the prevalence, anatomical features, as well as variance of the sternalis muscle in the Chinese population using multi-detector computed tomography (MDCT).

METHODS

We retrospectively reviewed 6,000 adult axial MDCT images to determine the overall and gender prevalence of the sternalis muscles. We also analyzed the side prevalence and anatomical features, including shape, size, location and course.

RESULTS

The sternalis muscle was present in 347 (5.8 %) of 6,000 adults. This muscle was more common in males (6.0 %, 187/3091) than in females (5.5 %, 160/2909). Among the 347 adults, 118 (34.0 %) had bilateral sternalis muscles; 148 (42.7 %) had right sternalis muscles; and 81 (23.3 %) had left sternalis muscles. The sternalis muscle was either flat or nodular and located superficial to the major pectoral muscles on CT axial transverse images. According to the muscle morphology and course, we classified sternalis muscles as three different types and nine subtypes. The muscles appeared with a single head and single belly in 58.5 %, double or multiple heads in 18.1 %, and double or multiple bellies in 23.4 %. The mean length, width and thickness were 111.1 ± 33.0, 17.7 ± 9.9 and 4.1 ± 1.7 mm measured on MDCT.

CONCLUSION

The sternalis muscle was highly prevalent in normal Chinese adults. MDCT is an effective method to demonstrate this muscle in vivo.

Development of the rectus abdominis and its sheath in the human fetus

PURPOSE

Although the rectus abdominis and its sheath are well known structures, their development in the human fetus is poorly understood.

MATERIALS AND METHODS

We examined rectus abdominis and sheath development in semiserial horizontal sections of 18 fetuses at 5-9 weeks of gestation.

RESULTS

Rectus muscle differentiation was found to commence above the umbilicus at 6 weeks and extend inferiorly. Until closure of the anterior chest wall via fusion of the bilateral sternal anlagen (at 7 weeks), the anterior rectal sheath originated from the external oblique and developed towards the medial margin of the rectus abdominis at all levels, including the supracostal part. After formation of the anterior sheath, fascial laminae from the internal oblique and transversus abdominis contributed to formation of the posterior rectus sheath. However, the posterior sheath was absent along the supracostal part of the rectus abdominis, as the transversus muscle fibers reached the sternum or the midline area. Therefore, it appeared that resolution of the physiological umbilical hernia (8-9 weeks) as well as chest wall closure was not required for development of the rectus abdominis and its sheath. Conversely, in the inferior part of the two largest fetal specimens, after resolution of the hernia, the posterior sheath underwent secondary disappearance, possibly due to changes in mechanical stress.

CONCLUSION

Upward extension of the rectus abdominis suddenly stopped at the margin of the inferiorly developing pectoralis major without facing the external intercostalis. The rectus thoracis, if present, might correspond to the pectoralis.

The sternalis muscle-incidental finding of a rare chest wall muscle variant during keloid excision-chest wall reconstruction

INTRODUCTION

The sternalis is a rare (strap-like) parasternal muscle that is well known to anatomists, but relatively unknown to clinicians, including surgeons. Familiarity with the muscle is important in avoiding potential confusion when incidentally encountered. When available, the muscle can be harvested for reconstruction of the chest wall or of nearby region.

PRESENTATION OF CASE

The patient is a 55-year-old man with significant sternal keloids secondary to a previous history of severe acne. The patient desires removal of the keloids. Hence, a decision was made to excise the keloids, followed by immediate reconstruction with a propeller flap. Intraoperative excision of the keloids and undermining of adjacent subcutaneous tissue revealed chest muscle fibers fitting the description of the sternalis muscle. The patient tolerated the procedure without any complications.

DISCUSSION

The sternalis muscle can be confused for a mass on mammography, but confusion is resolved by computed tomography/magnetic resonance imaging. It has unclear embryonic origin-perhaps a remnant of the panniculus carnosus and/or derivative of a primitive ventral-longitudinal muscle sheet that give rise to the sternocleidomastoid and the rectus abdominis muscles. It is uni- or bilateral and has 1 or 2 bellies. It originates in the intraclavicular region and inserts onto the rectus sheath, costal cartilages, lower ribs, or external oblique aponeurosis.

CONCLUSION

Not enough is known about the sternalis muscle to draw any conclusion about its utility in reconstructive surgery. It is hoped that cases will be presented in the foreseeable future describing its usage in reconstruction of the neck, chest, abdomen, and perhaps even other places.

The sternalis muscle: radiologic findings on MDCT

PURPOSE

The purpose of this study was to characterize and determine the prevalence of the sternalis muscle using 64-row multidetector computed tomography (MDCT).

MATERIALS AND METHODS

We retrospectively reviewed MDCT chest scans that were performed in a hospital during the course of a month. The study population consisted of 948 consecutive patients (511 males and 467 females). On the MDCT scans the sternalis muscle was defined as the longitudinal muscle lying on and superficial to the pectoralis major muscle.

RESULTS

The prevalence of the sternalis muscle was 10.5 %. The muscle was present more frequently in females (13.0 %) compared to males (8.4 %) (P = 0.02). In the majority of patients, the muscle was located longitudinally in the parasternal position; however, in two patients it was positioned across the sternum. One hundred twenty were flat types, while the remaining five had oblique shapes. The muscle mean height, width and depth were 77.9 ± 25.1, 19.4 ± 12.2 and 2.8 ± 1.3 mm, respectively. The muscle was wider in males compared to females (P < 0.001).

CONCLUSION

Using MDCT, its prevalence was shown to be 10.5 %. This variant muscle can be differentiated from other pathological structures using its specific characteristic appearance.

Sternalis muscle: an underestimated anterior chest wall anatomical variant

Over the recent years, an increased alertness for thorough knowledge of anatomical variants with clinical significance has been recorded in order to minimize the risks of surgical complications. We report a rare case of bilateral strap-like sternalis muscle of the anterior chest wall in a female cadaver. Its presence may evoke alterations in the electrocardiogram or confuse a routine mammography. The incidental finding of a sternalis muscle in mammography, CT, and MRI studies must be documented in a patient's medical records as it can be used as a pedicle flap or flap microvascular anastomosis during reconstructive surgery of the anterior chest wall, head and neck, and breast. Moreover, its presence may be misdiagnosed as a wide range of benign and malignant anterior chest wall lesions and tumors.

Variety of transversus thoracis muscle in relation to the internal thoracic artery: an autopsy study of 120 subjects

Background

The transversus thoracis muscle is a thin muscular layer on the inner surface of the anterior thoracic wall that is always in concern during harvesting of the internal thoracic artery. Because the muscle is poorly described in the surgical literature, the aim of the present study is to examine in details its variations.

Methods

The data was obtained at standard autopsies of 120 Caucasian subjects (Bulgarians) of both sexes (97 males and 23 females), ranging in age from 18 to 91 years (mean age 52.8 ± 17.8 years). The transversus thoracis morphology was thoroughly examined on the inner surface of the chest plates collected after routine incisions.

Results

An overall examination revealed that in majority of cases the transversus thoracis slips formed a complete muscular layer (left - 75.8%, right - 83.3%) or some of the slips (left - 22.5%, right - 15%) or all of them (left - 1.7%, right - 1.7%) were quite separated. Rarely (left - 3.3%, right - 5.8%), some fibrous slips of the transversus thoracis were noted. In 55.8% of the cases there was left/right muscle symmetry; 44.2% of the muscles were asymmetrical. Most commonly, the highest muscle attachment was to the second (left - 53.3%, right - 37.5%) or third rib (left - 29.2%, right - 46.7%). The sixth rib was the most common lowest attachment (left - 94.2%, right - 89.2%). Most frequently, the muscle was composed of four (left - 31.7%, right - 44.2%) or fifth slips (left - 53.3%, right - 40.8%).

Conclusions

This study provides detailed basic information on the variety of the transversus thoracic muscle. It also defines the range of the clearly visible, uncovered by the muscle part of the internal thoracic artery and the completeness of the muscular layer over it. The knowledge of these peculiar muscle-arterial relations would definitely be beneficial to cardiac surgeon in performing fast and safe arterial harvesting.

Use of the rectus sternalis in augmentation mammoplasty: case report and literature search

Breast augmentation is by far one of the most common aesthetic procedures currently performed by plastic surgeons. The plane of dissection for prosthesis placement is quite often partial submuscular. The rectus sternalis, an nomalous muscle, may interfere with the submuscular pocket dissection when an intraalveolar or submammary approach is used. The use of this muscle to cover the prosthesis in its most medial part is presented.

The Sternalis Muscles

OBJECTIVE

We studied the incidence and appearance of the sternalis muscles on multidetector computed tomography (MDCT) to permit the differentiation of the sternalis from significant pathologic condition.

METHODS

We retrospectively evaluated consecutive contrast-enhanced 16 row MDCT scans of the chest obtained in 1387 Korean patients (790 males and 597 females) between September 2003 and January 2005. All computed tomography scans were obtained in the supine position. Age ranges were 16 to 87 years and average was 59.2 years. Imaging analysis was based upon distribution (unilateral or bilateral, size, shape, and location). Statistical differences were evaluated by chi tests and Independent Samples t tests.

RESULTS

The sternalis muscle was present in 86 (6.2%) of 1387 patients. This muscle was more common in female (44 of 597, 7.3%) than in male (42 of 790, 5.3%) patients, but statistical significance was not noted (P=0.058). Twenty-three patients showed bilateral sternalis muscles. Among 63 patients with unilateral sternalis muscles, 28 patients showed left sternalis muscles and 35 patients showed right sternalis muscles. Unilateral distribution was more common. The height, AP diameter, and width of the sternalis muscle were not significantly different between unilateral and bilateral muscles (P=0.182, 0.911, and 0.114, respectively). The height and AP diameter showed no significant difference between male and female (P=0.470, 0.329, respectively) patients, but the width was wider in male (P<0.001) patients. All sternalis muscles showed flat appearance, except for 1 case. The sternalis muscles were located longitudinally in parasternal position in all cases.

CONCLUSIONS

The sternalis muscle is an unusual normal variant of the chest wall musculature running parallel to the sternum with various sizes and most sternalis muscles are flat on MDCT. Unilateral distribution is more common, and the size of muscle is larger in males. Its incidence is 6.2% in Korean population. Radiologists should be familiar with the image findings of the sternalis muscle to avoid any confusing pathologic lesions and facilitate its clinical use such as flap.

Left musculus sternalis

During routine dissection in the Morphological Sciences Department II of the Universidad Complutense de Madrid, the presence of a sternalis muscle was observed in the left hemithorax of a 70-year-old male cadaver. We report on its position, relationships, and innervation, as well as its clinical relevance, indicating some guidelines for its physical examination. We also present a brief overview of the existing literature regarding the nomenclature, historical reports, and incidence of this muscle.