Sternalis muscle, what every anatomist and clinician should know

Sternalis featuring tendomuscular fusion to the contralateral sternocleidomastoid: a cadaveric case report

PURPOSE

To report the morphologic and spatial relationships of a bilateral sternalis muscle variant.

METHODS

Routine cadaveric dissection in an undergraduate anatomy laboratory revealed two sternalis muscles parasternal to the sternal body. Subsequent fine prosection of the anterior thoracic wall and neck was carried out to uncover the soft tissue attachments of both sternalis muscles. Positional relationship to neighboring anterior thoracic and neck structures, and geometric dimensions of the muscle bellies and tendons, were documented.

RESULTS

Both sternalis muscles were imbedded in the pectoral fascia, with their muscle fibers running obliquely to the midsternal line. The right sternalis muscle was notably larger in length, width, and thickness compared to the sternalis muscle on the left. The right sternalis muscle featured a distinct superior cord-like intermediate tendon that traversed superolateral and fused directly with the contralateral sternomastoid and sterno-occipital portions of the left sternocleidomastoid muscle. The superior tendon of the left sternalis muscle was aponeurotic and affixed to the cord-tendon of the right sternalis muscle. A distinct tendinous entheses for the sternal head for both sternocleidomastoid muscles were noted at the manubrial body.

CONCLUSIONS

This case report describes a unique bilateral sternalis muscle variant with conjoined sternocleidomastoid muscle integration. This anatomical description of a sternalis-sternocleidomastoid muscle morphology may supplement radiographic interpretations and support diagnostic accuracy.

Sternalis Muscle: A Cadaveric Case Report of a Rare Variant With Multiple Branching

The sternalis muscle is a rare anatomical variant located in the anterior thoracic wall. Understanding variations in the sternalis muscle anatomy is essential for clinicians, especially radiologists and surgeons to prevent misdiagnosis and avoid complications during surgical procedures in the anterior thoracic region. We present a unique case of bilateral branched sternalis muscles. On either side, the sternalis muscle lies deep to the breast and superficial fascia and superficial to pectoralis major muscle and pectoral fascia. Each sternalis muscle is branched into medial and lateral slips with the medial slip larger than the lateral slip. The medial slip of the right sternalis was larger than the medial slip of the left sternalis. The lateral slip of the left sternalis was larger than the lateral slip of the right sternalis. The lateral slip of the left sternalis muscle has a curved course with superior-lateral convexity and inferomedial concavity. Near its middle, the left sternalis lateral slip is branched into two smaller slips separated by a narrow cleft. The left sternalis muscle in our report is a new variant with multiple branching, which cannot be matched to any type of the previously described classifications. In this case report, we discussed the need of modification of the currently available sternalis classification system to accommodate all types of the previously reported sternalis muscles including the branching pattern of this muscle.

Bilateral Sternalis Muscles: The Clinical Significance of This Rare Discovery

This case report explores the physical characteristics and clinical significance of the sternalis muscle, an uncommon anatomical variation of the anterior thoracic wall. If present, the sternalis muscle may distort diagnostic images and can be associated with incorrect interpretation of such medical images, misdiagnoses, and even surgical complications. As such, enhancing clinicians' knowledge of this muscle and improving its recognition is of the utmost importance. In this case report, a rare bilateral sternalis muscle that was discovered during an educational human cadaveric dissection of a 73-year-old Black male is described. The right sternalis muscle fibres extended from the mid-sternal level to the right sternocostal arch, measuring 11.5 cm in length and 3.4 cm at its largest width. In contrast, the smaller left sternalis muscle fibres measured only 5.6 cm in length and 1.2 cm at its greatest width. This rare bilateral presentation of the sternalis muscle is documented in approximately one-third of all reported sternalis cases with an associated estimated prevalence as low as 1.7% among the general population. Serving as a reminder of the intricate anatomical complexities that continue to challenge and intrigue medical professionals, this report advocates for continued education of anatomical variations to enhance patient care and medical practices.

Bilateral Sternalis Muscle With the Absence of Unilateral Sternocostal Part of the Pectoralis Major and Variation of Pectoralis Minor Muscles

This study aims to report a 57-year-old male cadaver with a rare muscular variation of the sterno-pectoral region. An unusual sternalis muscle was observed on both sides, arising from the external oblique muscle aponeurosis. The fibers converged upwards and medially in a curved course, producing a bundle 99.50 mm long on the right side and 74.60 mm on the left. The muscles on both sides were supplied by the second, third, and fourth intercostal nerves. In the right pectoralis major (PM) muscle, the sternocostal head was completely absent, and the clavicular head arose from the medial two-thirds of the clavicle, whereas abdominal fibers arose from the aponeurosis of the external abdominal oblique muscle and ran upward and laterally and joined the clavicular fibers with a wide triangular gap. On the left side, there was an anatomically normal PM muscle. The origin of the pectoralis minor was unusually high on both sides. The morphological variations of sterno-pectoral musculature have significant implications for clinical practice, which allows more precise surgical or radiological outcomes. Clinicoradiological evaluation of these variations is important to achieve appropriate dissection planes during chest wall surgery.

Sternalis Syndrome Misidentified by Multiple Specialties Responding to Botox Treatment: A Case Report and Literature Review

When a clinician, especially one who is specialized in primary care is faced with presenting complaints of deep, sharp, anterior chest pain, the most common differential diagnoses include cardiac and gastrointestinal pain. Musculoskeletal pain is thought of less frequently as a possible root cause. In this case report, we describe the clinical journey of a female athlete who presented with complaints of burning anterior chest pain. Her sternalis syndrome pain was first misdiagnosed as pain of cardiac origin, resulting in pacemaker placement into the patient's chest. The pain continued, and the same musculoskeletal pain was then presumed to be of gastrointestinal origin due to a previous history of gastroesophageal reflux disease (GERD). As a result of this misidentification, the patient underwent an unnecessary esophageal surgical procedure. Here, we identify the origins of sternalis syndrome pain, what other conditions the pain may be confused with, and how clinicians should not be quick to exclude musculoskeletal pain from a differential diagnosis of acute chest pain. We discuss effective treatments for sternalis syndrome and shed light on this less common cause of anterior chest pain to promote more accurate diagnosis and avoidance of unnecessary surgical interventions.

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.

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.

Pediatric chest wall masses: spectrum of benign findings on ultrasound

A palpable finding along the chest wall is a frequent indication for pediatric US. Accurate identification of benign lesions can reassure families and appropriately triage children who need follow-up, cross-sectional imaging, or biopsy. In this pictorial essay, we review chest wall anatomy, illustrate US techniques and discuss key US imaging features of common benign lesions and normal variants.

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.

Unilateral Sternalis With Double Slips: An Astounding Muscle, Often Unnoticed and Unknown

Discovery and variations of rectus sternalis muscle are occasionally seen in humans. However, during routine academic dissection of an adult male embalmed cadaver, a rare variant of the muscle was identified. The muscle had origin from the pectoral muscle and fascia and was inserted into external oblique aponeurosis along with the sixth rib and cartilage. It had double slips with the partial merging of the bellies. Knowledge regarding such unique muscle is important to anatomists for medical education as well as to surgeons during thoracic surgeries, in craniocaudal mammography where it can mimic breast mass and for using as muscle flap in the anterior chest wall, head and neck, and breast reconstructions.

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.

Sternalis is muscle: An anatomic variation and its clinical implications

This report presents a case description of sternalis muscle which is an accessory muscle of anterior thoracic wall. A 56-year-old woman underwent mastectomy for breast cancer along with free flap reconstruction, revealing the presence of aberrant sternalis muscle. It was divided transversely during partial rib resection to expose internal mammary vessels. The case proceeded with successful flap transfer. Clinical implications of this anatomic variation is discussed. The authors conclude that plastic surgeons should be aware of this muscular anomaly.

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.

The Five Diaphragms in Osteopathic Manipulative Medicine: Myofascial Relationships, Part 2

The article continues the anatomical review of the anterolateral myofascial connections of the five diaphragms in osteopathic manipulative medicine (OMM), with the most up-to-date scientific information. The postero-lateral myofascial relationships have been illustrated previously in the first part. The article emphasizes some key OMM concepts; the attention of the clinician must not stop at the symptom or local pain but, rather, verify where the cause that leads to the symptom arises, thanks to the myofascial systems. Furthermore, it is important to remember that the human body is a unity and we should observe the patient not as a series of disconnected segments but as multiple and different elements that work in unison; a dysfunction of tissue will adversely affect neighboring and distant tissues. The goal of the work is to lay solid foundations for the OMM and the five-diaphragm approach showing the myofascial continuity of the human body.

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.

Anatomical Variations of the Pectoralis Major Muscle: Notes on Their Impact on Pectoral Nerve Innervation Patterns and Discussion on Their Clinical Relevance

BACKGROUND

The presented study attempts to classify individual anatomical variants of the pectoralis major muscle (PM), including rare and unusual findings. Rare cases of muscular anomalies involving the PM or its tendon have been presented. An attempt has also been made to determine whether anatomical variations of the PM may affect the innervation pattern of the lateral and medial pectoral nerves.

MATERIAL AND METHODS

The research was carried out on 40 cadavers of both sexes (22 males, 18 females), owing to which 80 PM specimens were examined.

RESULTS

Typical PM structure was observed in 63.75% of specimens. The most frequently observed variation was a separate clavicular portion of the PM. In one female cadaver (2.5% of specimens) the hypotrophy of the clavicular portion of the PM was noticed. In two male cadavers (5% of specimens) the fusion between the clavicular portion of the PM and the deltoid muscle was observed. In one of those cadavers, small sub-branches of the lateral pectoral nerve bilaterally joined the clavicular portion of the deltoid muscle. The detailed intramuscular distribution of certain nerve sub-branches was visualized by Sihler's stain. PM is mainly innervated by the lateral pectoral nerve. In all specimens stained by Sihler's technique, the contribution of the intercostal nerves in PM innervation was confirmed.

CONCLUSIONS

Surgeons should be aware of anatomic variations of the PM both in planning and in conducting surgeries of the pectoral region.

Chondroepitrochlearis and a supernumerary head of the biceps brachii

Unique variants of the pectoralis major and biceps brachii were found during a routine student dissection of a 96-year-old Caucasian female's axilla and brachium. The donor cadaver had bilateral presentation of a muscle originating from the pectoralis major, near the lateral lip of the intertubercular groove, extending obliquely to insert on the medial intermuscular septum and medial epicondyle of the humerus. This muscle variant is currently described as a rare presentation of the chondroepitrochlearis, potentially a remnant of the panniculus carnosus in man. Often considered to be a thin, slender muscle taking origin from the true ribs, the right-side chondroepitrochlearis described in this report was notably larger-to the authors' knowledge-than all other published cases, measuring 38.1 mm at the widest point. Meanwhile, another small muscle originating on the posterior surface of the pectoralis major tendon was present. Due to its insertion, the muscle was identified as a supernumerary portion, or a third head, of the biceps brachii. The proximal attachment of both the chondroepitrochlearis and the third head of the biceps brachii could impose functional limitations on the pectoralis major.

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.

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.