Fibromatosis colli (FMC), also termed sternocleidomastoid tumor of infancy, pseudotumor of infancy, and infancy sternocleidomastoid pseudotumor, is an uncommon (incidence: 0.4%–1.3% of live births),

congenital A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...

tumor in one of the two

sternocleidomastoid The sternocleidomastoid muscle is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck. The sternocleidomastoid is innervated by the access ...

neck muscles although rare cases have presented with a FMC tumor in both sternocleidomastoid muscles. A tumor is here defined as a growth of tissue that is not coordinated with the normal surrounding tissue and persists in growing even if the original trigger for its growth is removed. FMC tumors are benign growths that may cause disfigurements but are not cancers and do not metastasize (i.e. spread) to distant tissues. As judged by microscopic

cytology Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and ...

analyses, fibromatosis colli tumors consist of spindle-shaped fibroblasts (i.e. the most common cell type in

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

) located in a background of

collagen fibers Type I collagen is the most abundant collagen of the human body. It forms large, eosinophilic fibers known as collagen fibers. It is present in scar tissue, the end product when tissue heals by repair, as well as tendons, ligaments, the endomys ...

, decomposing

skeletal muscle fibers Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...

, and, in some cases, regenerating skeletal muscle fibers. The fibroblasts have a completely normal appearance with no evidence suggesting that they are malignant. The

World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...

in 2020 classified fibromatosis colli in the category of benign

fibroblastic and myofibroblastic tumors Fibroblastic and myofibroblastic tumors (FMTs) develop from the mesenchymal stem cells which differentiate into fibroblasts (the most common cell type in connective tissue) and/or the myocytes/myoblasts that differentiate into muscle cells. FMTs ...

. In the majority of cases, FMC tumors decrease in size and completely resolve by the newborn's second year. If left untreated, however, a significant percentage of cases progress to, and are the most frequent cause of, congenital muscular torticollis, i.e. an abnormal, asymmetrical head or neck position commonly called wry neck. Untreated FMC tumors may also progress to

facial asymmetry Facial symmetry is one specific measure of bodily symmetry. Along with traits such as averageness and youthfulness it influences judgments of aesthetic traits of physical attractiveness and beauty. For instance, in mate selection, people have be ...

plagiocephaly Plagiocephaly, also known as flat head syndrome, is a condition characterized by an asymmetrical distortion (flattening of one side) of the skull. A mild and widespread form is characterized by a flat spot on the back or one side of the head cause ...

(i.e. flattened head), permanent loss of neck mobility,

scoliosis Scoliosis is a condition in which a person's spine has a sideways curve. The curve is usually "S"- or "C"-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis does not t ...

(i.e. sidewise curvature of the spine), or other structural disfigurements that result from compensatory mechanisms.

Presentation

FMC tumors most commonly present as slow-growing, firm, mobile, nontender, spindle-shaped masses in the lower two-thirds of the sternocleidomastoid muscle of infants within 8 weeks (average: 24 days) of delivery. At diagnosis, these infants' heads may tilt toward the side with the mass while their chins tilt to the opposite, uninvolved side. This tilting is due to sternocleidomastoid muscle contracture. FMC tumors are more common in males and the right sternocleidomastoid muscle although very rare cases present with bilateral tumors. Untreated, the masses may continue to grow for weeks after birth but then stabilize, start regressing after 4–8 months of life, and over the ensuing 1–2 years typically fully resolve. In three studies, >25%, >50% and >80% of these infants have had difficult deliveries such as a

breech birth A breech birth is when a baby is born bottom first instead of head first, as is normal. Around 3–5% of pregnant women at term (37–40 weeks pregnant) have a breech baby. Due to their higher than average rate of possible complications for the ...

, delivery requiring forceps, primigravida birth (i.e. mother's first child), prolonged, difficult

labor Labour or labor may refer to: * Childbirth, the delivery of a baby * Labour (human activity), or work ** Manual labour, physical work ** Wage labour, a socioeconomic relationship between a worker and an employer ** Organized labour and the labour ...

, or delivery by

Caesarean section Caesarean section, also known as C-section or caesarean delivery, is the surgical procedure by which one or more babies are delivered through an incision in the mother's abdomen, often performed because vaginal delivery would put the baby or mo ...

. From 6-20% of newborns with fibromatosis colli also present with other congenital lesions such as

hip dysplasia Hip dysplasia is an abnormality of the hip joint where the socket portion does not fully cover the ball portion, resulting in an increased risk for joint dislocation. Hip dysplasia may occur at birth or develop in early life. Regardless, it doe ...

or, less commonly, facial asymmetry.

Pathology

Microscopic

histopathological Histopathology (compound of three Greek words: ''histos'' "tissue", πάθος ''pathos'' "suffering", and -λογία ''-logia'' "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Spec ...

analyses of biopsied FMC tumor tissues typically find benign-appearing, spindle-shaped fibroblasts, decomposing skeletal muscle fibers, and, in some cases, regenerating skeletal muscle fibers in a

collagen fiber Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whol ...

-containing background. If necessary, these tumors are typically diagnosed by microscopic examination of

fine-needle aspiration Fine-needle aspiration (FNA) is a diagnostic procedure used to investigate lumps or masses. In this technique, a thin (23–25 gauge (0.52 to 0.64 mm outer diameter)), hollow needle is inserted into the mass for sampling of cells that, aft ...

samples rather than the more invasive approach of tumor

biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a diseas ...

sampling. The aspirates show scant to moderately cellular, scattered, oval-shaped to spindle-shaped fibroblasts, naked nuclei (i.e. cell nuclei virtually devoid of other cell elements such as the

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

), wisps of collagen, atrophic, degenerating muscle fibers, regenerating muscle fibers, and intact skeletal muscle cells containing multiple nuclei. There is no evidence of

inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...

hemorrhage Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...

, cell

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

, or rapidly dividing and/or proliferating cells.

Etiology

It has been postulated that the FMC tumor mass itself is a remnant of a

hematoma A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillary, capillaries. A he ...

caused by tissue injury occurring during delivery. However, there are no features of hematomas (e.g.

hemosiderin Hemosiderin image of a kidney viewed under a microscope. The brown areas represent hemosiderin Hemosiderin or haemosiderin is an iron-storage complex that is composed of partially digested ferritin and lysosomes. The breakdown of heme gives rise ...

released by dying

red blood cells Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''k ...

) in theses lesions at diagnosis and no evidence of trauma (e.g. overlying skin changes or discolorations) at birth in infants who later present with FMC tumors. It has also been suggested that venous outflow obstruction occurring in the

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...

while in the uterus or during delivery leads to degeneration of sternocleidomastoid muscle fibers and subsequent fibrosis of the damaged areas. Finally, it has been suggested that an injury due to poor fetal head positioning in the uterus produces a

compartment syndrome Compartment syndrome is a condition in which increased pressure within one of the body's anatomical compartments results in insufficient blood supply to tissue within that space. There are two main types: acute and chronic. Compartments of the ...

-like pressure-induced injury to the sternocleidomastoid muscle that results in muscle cell death followed by tissue fibrosis and the usual pathology of FMC tumors.

Diagnosis

The recommended first step after clinically detecting a sternocleidomastoid mass in a newborn infant is Doppler ultrasonography combined with duplex ultrasonography. This method commonly reveals diagnostic (up to 100% sensitivity rates) findings of diffuse or focal enlargement of sternocleidomastoid muscle that has no

cysts A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubble) ...

or other ultrasonography-detected abnormalities. If these imaging findings are not diagnostic,

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...

may clarify the diagnosis. If the findings still remain unclear, microscopic examination of fine needle asperates taken from the tumor will, when combined with the imaging findings, the lesion’s natural history, and its clinical presentation, likely confirm the diagnosis of FMC in virtually all cases.

Treatment and prognosis

Prompt diagnosis and treatment of FMS is crucial for avoiding the impairments that may follow long-term mal-positioning of infant's head such as permanent facial asymmetry, flattened head, loss of neck mobility, and scoliosis. About 95% of infants with minimal limitations in their head's mobility show improvements in this mobility after four weeks of an active home stimulation program (i.e. observation, massage, and active and passive stretching), while ~91% of infants with more severe movement limitations show good results after three sessions of targeted physiotherapy over a 3–4 month period. The recommended treatment for infants who show no improvements in mobility after one year of physical therapy or who initially present at >12 months of age is surgical

tenotomy A tenotomy is a surgical act which involves the division of a tendon. It and related procedures are also referred to as tendon release, tendon lengthening, and heel-cord release. When it involves the Achilles tendon, it is called "Achillotenotomy ...

(i.e. cutting) of one of the

tendons A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...

on the involved sternocleidomastoid muscle. Tenotomy may use the open surgical (i.e. cutting of skin) approach or endoscopic (i.e. percutaneous) approach. The overall prognosis of FMS tumors is good using these treatment measures. Infants presenting with FMS should be examined for the presence of

References