Accessory

by S. Serkan Sezer MD

The word accessory is one of the most widely used terms in anatomical, surgical, and clinical medical literature. From accessory bones of the skeleton to a “secondary” cranial nerve, from accessory pathways in the heart to accessory muscles of breathing, the word frequently denotes structures that perform supportive or auxiliary functions in the body. Although accessory structures often go unnoticed in everyday life, they can be of considerable clinical importance.

Definition

In English medical dictionaries, the term is transcribed as /əkˈsesəri/ and given in two grammatical forms:

As a noun: “Something which helps something else to happen or operate, but may not be very important in itself.”

As an adjective: “Helping something else to happen or operate.”

In medical usage, the word carries several related meanings:

  1. Anatomically — a structure that is additional or supplementary to a principal structure
  2. Physiologically — an organ or system that supports the main function
  3. Surgically — additional tissues encountered during operative procedures
  4. Pathologically — accessory structures that play a role in disease processes

The word derives from the Latin accessorius, meaning “additional” or “supplementary.”

Anatomical Accessory Structures

The human body contains numerous “accessory” anatomical structures, many of which are clinically very important.

Accessory Nerve (Cranial Nerve XI)

One of the best-known accessory structures:

  • Eleventh cranial nerve
  • Also known as the spinal accessory nerve
  • Has two roots: cranial and spinal
  • Innervates the sternocleidomastoid and trapezius muscles
  • Damage causes weakness of head turning and shoulder shrugging
  • May be injured in neck dissection surgery
  • Loss of function may be seen after lymph node biopsies

Accessory Bones

Small, additional bones found in the skeletal system:

  • Os trigonum — accessory bone at the back of the ankle
  • Os tibiale externum — accessory bone on the inner side of the foot
  • Sesamoid bones — small bones found within tendons
  • Wormian bones — additional bones in the sutures of the skull
  • Cervical rib — extra rib found in the neck region

These accessory bones are usually congenital and asymptomatic but can sometimes cause pain, nerve compression, or vascular impingement.

Accessory Muscles of Breathing

Muscles that assist breathing alongside the main respiratory muscle (the diaphragm):

  • Sternocleidomastoid muscle
  • Scalene muscles
  • Pectoral muscles
  • Trapezius
  • Intercostal muscles
  • Abdominal muscles

Use of these muscles is normally minimal at rest. During exercise or in respiratory disease, however, they come into prominent action. The use of accessory muscles is an important clinical sign in conditions such as severe asthma attacks, chronic obstructive pulmonary disease (COPD), and respiratory failure.

Accessory Spleen

  • Splenule or supernumerary spleen
  • Found in approximately 10–30% of the population
  • Usually small (1–2 cm in size)
  • Most often located near the hilum of the spleen
  • Generally asymptomatic
  • Important to recognise during splenectomy; if not removed, can cause persistence of disease
  • May be mistaken for tumours on imaging studies

Accessory Pancreatic Duct

  • Duct of Santorini
  • An additional duct alongside the main pancreatic duct (duct of Wirsung)
  • Opens into the duodenum via the minor papilla
  • Variations may be associated with pancreatitis
  • Pancreas divisum is a relevant developmental anomaly

Accessory Salivary Glands

  • Minor salivary glands
  • Numbering 600–1000 in total
  • Distributed across the lips, cheeks, palate, and tongue
  • Important in maintaining a moist oral cavity
  • Possible sites of origin of salivary gland tumours

Accessory Lacrimal Glands

  • Help to keep the eye surface moist
  • Glands of Krause and Wolfring
  • Maintain basal tear production
  • Important when the main lacrimal gland is damaged

Accessory Reproductive Organs

  • In men — seminal vesicles, prostate, bulbourethral glands
  • In women — Bartholin’s glands, Skene’s glands
  • Contribute to fertility and sexual function

Accessory Sinuses

  • The paranasal sinuses are also referred to as “accessory” cavities
  • Frontal, maxillary, ethmoid, and sphenoid sinuses
  • Lighten the weight of the skull
  • Function in voice resonance
  • Common site of sinusitis

Accessory Pathways in the Cardiovascular System

A very important concept in cardiology:

Accessory Conduction Pathways

In the normal heart, the electrical signal is conducted only between the atria and ventricles via the AV node. In some people, however, additional (“accessory”) conducting fibres are present:

  • Bundle of Kent — most common, causes Wolff–Parkinson–White (WPW) syndrome
  • Mahaim fibres
  • James fibres

Clinical Significance

These accessory pathways can cause:

  • Pre-excitation syndromes (notably WPW)
  • Supraventricular tachycardia
  • Atrial fibrillation
  • Sudden cardiac death (rare but a serious risk)

Treatment

  • Catheter ablation — current first-line treatment
  • Drug therapy
  • Electrophysiological evaluation

Accessory Organs of the Digestive System

The principal organs of the digestive tract are the oesophagus, stomach, and intestines. The accessory organs are:

Liver

  • The largest gland of the body
  • Bile production
  • Detoxification
  • Metabolic regulation

Gallbladder

  • Storage and concentration of bile
  • Release of bile during digestion

Pancreas

  • Digestive enzymes
  • Endocrine function (insulin, glucagon)

Salivary Glands

  • Saliva production
  • Initial digestion
  • Lubrication of food

These structures are not directly part of the gastrointestinal tract but are essential for normal digestion.

Accessory Organs of the Skin

The “accessory structures” of the skin are also of clinical importance:

  • Hair and hair follicles
  • Sebaceous glands
  • Sweat glands (eccrine and apocrine)
  • Nails
  • Sensory receptors

These structures support the protective, thermoregulatory, and sensory functions of the skin.

Accessory in Surgery

The concept also has several specific meanings in surgical practice:

Accessory Incision

  • Additional incisions made during the main operation
  • For drainage or improved access
  • Particularly used in laparoscopic surgery

Accessory Instruments

  • Equipment used in addition to the main surgical instruments
  • Endoscopic accessories
  • Robotic surgery attachments

Accessory Procedures

  • Additional procedures performed during the principal operation
  • For example, appendicectomy during cholecystectomy

Accessory Findings in Imaging

In radiology, “accessory” findings are often very important:

  • Accessory renal arteries — important when planning renal surgery
  • Accessory hepatic veins — significant in liver surgery
  • Accessory lobes of the lung — anatomical variations
  • Accessory thyroid tissue — important in thyroid surgery

These variations are determined preoperatively with CT, MRI, or angiography.

Accessory Cells

In histology and immunology, “accessory” cells perform important functions:

Immune System Accessory Cells

  • Dendritic cells — present antigens
  • Macrophages — phagocytic cells
  • B cells — when acting as antigen-presenting cells

These cells support the function of T lymphocytes and play a key role in initiating immune responses.

Hormonal Accessory Cells

  • Sertoli cells — support spermatogenesis
  • Follicular cells — support egg development
  • Granulosa cells — support hormone production

Accessory in Genetics

In genetics, “accessory” structures are also recognised:

  • Accessory chromosomes — extra small chromosomes
  • B chromosomes — additional chromosomes in some species
  • Accessory genes — supportive genetic elements

Accessory Equipment in Clinical Practice

A wide range of “accessory” items are used in clinical practice:

Diagnostic Accessories

  • Otoscope accessories — different size specula
  • Stethoscope accessories — paediatric heads, extension tubing
  • Endoscope accessories — biopsy forceps, brushes, snares

Treatment Accessories

  • Wheelchair accessories — cushions, head supports, accessory wheels
  • Bed accessories — side rails, head supports
  • Orthotic accessories — supports, pads
  • Prosthetic accessories — covers, attachment elements

Hearing Aid Accessories

  • Different sizes of ear moulds
  • Cleaning equipment
  • Battery chargers
  • Bluetooth accessories

Spectacle Accessories

  • Cleaning equipment
  • Carrying cases
  • Spare lenses
  • Tinted clip-ons

Accessory in Public Health

The concept also has applications in public health:

  • Accessory health services — services that support the main healthcare system
  • Home care accessories — equipment used in domiciliary care
  • Rehabilitation accessories — tools used in physical therapy
  • Emergency accessories — equipment used in first aid

Accessory Structures and Disease

Some accessory structures may be involved in disease processes:

Risk of Cancer

  • Tumours of accessory salivary glands
  • Cancers arising in accessory thyroid tissue
  • Tumours of accessory adrenal tissue

Persistence of Disease

  • After splenectomy, recurrence of disease due to an undetected accessory spleen
  • After thyroidectomy, persistence of hyperthyroidism due to accessory thyroid tissue
  • After parathyroidectomy, persistence of hyperparathyroidism due to accessory parathyroid glands

Diagnostic Challenges

  • Accessory organs may be mistaken for tumours on imaging
  • Anatomical variations encountered during surgery
  • Difficulties in radiological interpretation

Clinical Significance and Practical Use

Several principles should be borne in mind regarding accessory structures:

Importance of Anatomy Knowledge

  • Healthcare professionals must be familiar with anatomical variations
  • Surgeons must consider accessory structures during operations
  • Radiologists must recognise such variations

Patient Information

  • Information about variations identified on imaging
  • Notes about variations encountered during surgery
  • Sharing relevant family history information

Preoperative Planning

  • Detailed imaging studies
  • Identification of accessory structures
  • Tailoring of the surgical approach

Postoperative Follow-up

  • Monitoring for the existence of undetected accessory structures
  • Investigation when symptoms persist
  • Long-term follow-up planning

Examples of Common Accessory Variations

A few accessory variations are particularly common:

Cervical Rib

  • Around 0.5–1% of the population
  • Usually asymptomatic
  • May cause thoracic outlet syndrome
  • Surgery may be required

Os Trigonum

  • 10–25% of the population
  • Common cause of posterior ankle pain
  • Particularly common in ballet dancers
  • May require treatment

Accessory Renal Arteries

  • 25–30% of the population
  • Important in transplant surgery
  • May contribute to hypertension
  • May be associated with renal anomalies

Accessory Spleen

  • 10–30% of the population
  • Usually incidentally detected
  • Important after splenectomy
  • May be mistaken for tumours on imaging

Importance of Accessory Concepts in Education

In medical education, accessory structures are of particular importance:

  • Anatomy lessons — teaching of variations
  • Surgical training — recognition of anatomical variations
  • Radiology training — interpretation of variations
  • Clinical practice — patient-tailored approach

Future Developments

Research in the field continues:

  • 3D imaging technologies — better identification of variations
  • Artificial intelligence — automatic detection of variations
  • Personalised surgery — patient-specific surgical planning
  • Genetic research — molecular basis of variations
  • Embryological research — understanding the development of variations

Disclaimer

The information provided here is intended for general informational and educational purposes only and does not constitute medical advice, diagnosis, or treatment. If anatomical variations or accessory structures have been identified in your body, please discuss them with a qualified healthcare professional. Surgical and medical decisions should always be made together with an appropriately qualified physician. Do not rely on the content of this article when making decisions about your own or another person’s medical care.