Anatomy knowledge required to understand complication of Ischio-anal Abscess

 Ischioanal Abscess

• Definition: the abscess in  the ischioanal fossa, located between the anal canal  and the external sphincter muscles.

• Features:

• It creates severe pain, swelling, and fever.

•  The ischioanal fossa contains fat and connective tissue along with the anal glands. Infection of these glands can lead to the formation of an abscess within this anatomical space.

• Often develops as a result of an infection in the anal glands.

• Anatomical Explanation: a surgeon needs following anatomical knowledge to understand this clinical condition 

• Anatomy of Ischioanal fossa: It is bounded superiorly by the pelvic diaphragm, laterally by the obturator internus muscle, and medially by the anal canal.The ischioanal fossa contains fat, connective tissue, and anal glands.

•  interior of anal canal and location of anal gland

• It is situated below the dentate line, and it is area in lined by  stratified squamous epithelium, this area contains numerous sensory nerve endings, making it sensitive to pain, 

• Anal glands, also known as anal sinuses or crypts, are located within the anal canal and around the anal opening. They are small tubular structures that extend into the submucosa of the anal canal.These glands secrete mucus, which helps with lubrication during defecation and protects the anal canal from irritation.

• anatomy of external anal sphincter,is a striated muscle that surrounds the anal canal.

• It plays a crucial role in controlling bowel movements and maintaining continence.

• An ischioanal abscess can cause pain and discomfort due to its proximity to the external anal sphincter.

• Anatomy of pelvic diaphragm The pelvic diaphragm is a muscular partition that separates the pelvic cavity from the perineum. The superior border of the ischioanal fossa is formed by the pelvic diaphragm.

Clinical anatomy : internal and external hemorrhoids

 Hemorrhoids, also known as piles, are vascular structures located in the anal canal. They consist of clusters of blood vessels, smooth muscle, and connective tissue.

Anatomically, hemorrhoids are classified into two main types:

1. Internal Hemorrhoids: These hemorrhoids originate above the dentate line within the anal canal. The dentate line is a transitional area between the internal and external lining of the anal canal. Internal hemorrhoids are covered by a mucous membrane, which lacks pain receptors, hence they are usually painless unless they prolapse and become thrombosed. Internal hemorrhoids are supplied by branches of the superior rectal artery, which is a branch of the inferior mesenteric artery, making them part of the portal venous system. Increased pressure in the portal venous system, such as due to constipation or straining during bowel movements, can cause dilation and swelling of these veins, leading to the development of internal hemorrhoids.

2. External Hemorrhoids: These hemorrhoids originate below the dentate line and are covered by anoderm, which contains pain receptors. External hemorrhoids are supplied by branches of the inferior rectal artery, which is a branch of the pudendal artery, making them part of the systemic venous system. Factors such as increased intra-abdominal pressure or pregnancy can lead to enlargement and inflammation of these veins, contributing to the development of external hemorrhoids. External hemorrhoids may cause pain and discomfort, especially during bowel movements or when irritated.

Both internal and external hemorrhoids can become symptomatic when they swell, prolapse, thrombose, or become inflamed. Symptoms may include rectal bleeding, itching, discomfort, and pain. Treatment options range from conservative measures such as dietary modifications, topical treatments, and lifestyle changes to more invasive interventions like rubber band ligation, sclerotherapy, or surgical excision, depending on the severity and symptoms of the hemorrhoids.

Summary of internal and external hemorrhoids

Internal Hemorrhoids:

1. Origin: Above the dentate line in the anal canal.

2. Lining epithelium : it is covered by simple columnar epithelium 

3. Nerve Supply: it is supply by  Autonomic nerves, so it is typically painless.

4. Blood Supply: Superior rectal artery from the portal venous system.

5. Causes: Increased portal venous pressure from factors like constipation or straining during bowel movement.

External Hemorrhoids:

1. Origin: Below the dentate line in the anal canal.

2. Lining epithelium : it is covered by stratified squamous epithelium 

3. Nerve Supply: it is painful because it is supplied by  Somatic nerves, particularly the pudendal nerve.

4. Blood Supply: Inferior rectal artery from the systemic venous system.

5. Causes: Increased intra-abdominal pressure or pregnancy-related factors leading to enlargement and inflammation.

The dilator pupillae, the muscle of iris

  

 The dilator pupillae muscle is a ring of contractile cells within the iris. These cells are arranged radially, such that their contraction facilitates pupillary dilation (mydriasis). The dilator pupillae muscle receives innervation from the sympathetic nervous system.

Gross anatomy

The dilator pupillae muscle is a circumferential, spoke-like arrangement of contractile myoepithelial cells located in the mid-periphery of the posterior leaf of the iris, anterior to the pigmented epithelium. Like the sphincter pupillae muscle, it is located posterior to the rich connective tissue stroma and neurovasculature of the anterior iris leaf 

Innervation

The dilator pupillae muscle is innervated by the sympathetic nervous system. Postganglionic sympathetic fibers project from the superior cervical ganglion to join the carotid plexus. These fibers then course with the ophthalmic artery, forming a number of long ciliary nerves that supply the dilator pupillae muscle

Action

Contraction of the dilator pupillae muscle facilitates dilation of the pupil (mydriasis). This increases the amount of light impinging on the retina

Clinical importance

• alongside endogenous sympathetic stimulation, sympathomimetic drugs (e.g. stimulants) may act on the dilator pupillae muscle, resulting in mydriasis

• prolonged significant mydriasis narrows the iridocorneal angle for aqueous humor drainage, increasing the risk of closed angle glaucoma

• the miosis seen in patients with Horner syndrome is mediated by inactivation of the dilator pupillae muscle due to a lesion interrupting sympathetic outflow

is a ring of contractile cells within the iris. These cells are arranged radially, such that their contraction facilitates pupillary dilation (mydriasis). The dilator pupillae muscle receives innervation from the sympathetic nervous system.

Gross anatomy

The dilator pupillae muscle is a circumferential, spoke-like arrangement of contractile myoepithelial cells located in the mid-periphery of the posterior leaf of the iris, anterior to the pigmented epithelium. Like the sphincter pupillae muscle, it is located posterior to the rich connective tissue stroma and neurovasculature of the anterior iris leaf 

Innervation

The dilator pupillae muscle is innervated by the sympathetic nervous system. Postganglionic sympathetic fibers project from the superior cervical ganglion to join the carotid plexus. These fibers then course with the ophthalmic artery, forming a number of long ciliary nerves that supply the dilator pupillae muscle

Action

Contraction of the dilator pupillae muscle facilitates dilation of the pupil (mydriasis). This increases the amount of light impinging on the retina

Clinical importance

• alongside endogenous sympathetic stimulation, sympathomimetic drugs (e.g. stimulants) may act on the dilator pupillae muscle, resulting in mydriasis

• prolonged significant mydriasis narrows the iridocorneal angle for aqueous humor drainage, increasing the risk of closed angle glaucoma

• the miosis seen in patients with Horner syndrome is mediated by inactivation of the dilator pupillae muscle due to a lesion interrupting sympathetic outflow

Sphincter pupillae

 Sphincter pupillae is a circular muscle, about 1 millimeter wide. It is located in the pupillary zone of stromal layer of the iris, attaching to and encircling the pupillary margin of iris. The muscle itself consists of six to eight circles of smooth muscle fibers, between of which are found the nerves and blood vessels that supply each fiber. 

Development : ectoderm 

Innervation

The sphincter pupillae receives parasympathetic innervation from the postganglionic fibers of ciliary ganglion, called short ciliary nerves, which are the branches of oculomotor nerve (CN III). Note that these particular nerve fibers originate from the accessory nucleus of oculomotor nerve (Edinger-Westphal) - a general visceral efferent nucleus - which provides autonomic (involuntary) control to this muscle.

Function

When contracting, the sphincter pupillae constricts the pupil, which is called miosis. This action happens during accommodation and pupillary light reflexes.

 

Accommodation

Accommodation is a reflexive event that adapts the eyes for observing close objects after being focused on distant ones. The reflex pathway includes optic nerve (CN II), visual and frontal cortex, oculomotor and accessory oculomotor nuclei and oculomotor nerve (CN III).

 

Once the eyes need to focus on a near object, the optic nerve sends signals to the visual cortex, which then stimulates the eye field within frontal cortex. The frontal neurons then send fibers to the ipsilateral oculomotor nucleus (unicortical innervation), and to both ipsi- and contralateral accessory oculomotor nuclei (bicortical innervation). The oculomotor nerve sends these signals to the ciliary ganglion, which then outsources the final stimuli via its two sets of branches;

 

Short ciliary nerves that cause the contraction of sphincter pupillae and miosis

Long ciliary nerves which stimulate the medial recti and ciliary muscles; the former causes the convergence of the eyeballs, while the latter thickens the lens increasing its refractive power

Pupillary light reflex

The pupillary light reflex happens when the eyes are exposed to bright light and the amount of light that falls onto the retina needs to be decreased in order to maintain clear vision. The reflex arc includes optic nerve (CN II), pretectal nucleus of midbrain, accessory oculomotor nucleus and oculomotor nerve (CN III).

 

Once the retinal photoreceptors detect light, the optic nerve sends a neural impulse to the pretectal nucleus. The pretectal nucleus stimulates the accessory oculomotor nucleus, which in turn innervates and constricts the sphincter pupillae via the short ciliary nerves. As pretectal nucleus connects to both accessory oculomotor nuclei, stimulation and miosis of one eye (direct pupillary light reflex) will always be followed by miosis on non-stimulated eye (indirect pupillary light reflex).

Anatomy of iris

 Anatomy of Iris 

Iris is a circular pigmented diaphragm which is situated between the cornea and the lens 

Parts : It has 

Two margins 

• Peripheral margin attached with anterior surface of ciliary body : 

• Central circular margin known as pupil c

Two zones : 

• Ciliary zone contain ciliary crypts 

• Pupillary zone  contain pupillary ruff the reflected area of posterior pigmented area 

• Two zone is separated by collaratte a smooth ridge of tissue  

Shape: flatten cone with central opening, iris is push forward due to the anterior surface of the lens 

Iris divide anterior segment of eyeball into anterior and posterior chamber , both the chamber filled by aqueous humor which circulate through the opening of pupil 

Histology of iris 

From before backwards , The iris is composed of three layers:

1. Anterior surface of the iris :  an outer discontinuous layer of melanocytes and fibroblasts; 

2. Stroma of the iris the intermediate fibrous layer (FL), housing pigment cells (Pc) and fibroblasts; 

3. Muscle layer : 

• smooth muscle near the pupil , 

• smooth muscle in the deeper part of stroma 

4. Anterior Pigmented epithelium

5. Posterior pigmented epithelium

Anterior surface of the iris : 

The anterior surface of the iris is not covered by a distinct endothelium. Instead, it is formed by layers of branched fibroblasts and melanocytes, which blend with the pectinate ligament derived from the Descemet’s membrane of the cornea.

Stroma of the iris 

It contains collagen fibers, fibroblasts, melanocytes and blood vessels and nerves , sphincter and dilator pupillae muscles. Stromal spaces are in free communication with the fluid of the anterior chamber 

Sphincter pupillae is a circular muscle, about 1 millimeter wide. It is located in the pupillary zone of stromal layer of the iris, attaching to and encircling the pupillary margin of iris. The muscle itself consists of six to eight circles of smooth muscle fibers, between of which are found the nerves and blood vessels that supply each fiber. 

Development : ectoderm 

Innervation

The sphincter pupillae receives parasympathetic innervation from the postganglionic fibers of ciliary ganglion, called short ciliary nerves, which are the branches of oculomotor nerve (CN III). Note that these particular nerve fibers originate from the accessory nucleus of oculomotor nerve (Edinger-Westphal) - a general visceral efferent nucleus - which provides autonomic (involuntary) control to this muscle.

Function

When contracting, the sphincter pupillae constricts the pupil, which is called miosis. This action happens during accommodation and pupillary light reflexes.

 

Accommodation

Accommodation is a reflexive event that adapts the eyes for observing close objects after being focused on distant ones. The reflex pathway includes optic nerve (CN II), visual and frontal cortex, oculomotor and accessory oculomotor nuclei and oculomotor nerve (CN III).

 

Once the eyes need to focus on a near object, the optic nerve sends signals to the visual cortex, which then stimulates the eye field within frontal cortex. The frontal neurons then send fibers to the ipsilateral oculomotor nucleus (unicortical innervation), and to both ipsi- and contralateral accessory oculomotor nuclei (bicortical innervation). The oculomotor nerve sends these signals to the ciliary ganglion, which then outsources the final stimuli via its two sets of branches;

 

Short ciliary nerves that cause the contraction of sphincter pupillae and miosis

Long ciliary nerves which stimulate the medial recti and ciliary muscles; the former causes the convergence of the eyeballs, while the latter thickens the lens increasing its refractive power

Pupillary light reflex

The pupillary light reflex happens when the eyes are exposed to bright light and the amount of light that falls onto the retina needs to be decreased in order to maintain clear vision. The reflex arc includes optic nerve (CN II), pretectal nucleus of midbrain, accessory oculomotor nucleus and oculomotor nerve (CN III).

 

Once the retinal photoreceptors detect light, the optic nerve sends a neural impulse to the pretectal nucleus. The pretectal nucleus stimulates the accessory oculomotor nucleus, which in turn innervates and constricts the sphincter pupillae via the short ciliary nerves. As pretectal nucleus connects to both accessory oculomotor nuclei, stimulation and miosis of one eye (direct pupillary light reflex) will always be followed by miosis on non-stimulated eye (indirect pupillary light reflex).

 The dilator pupillae muscle is a ring of contractile cells within the iris. These cells are arranged radially, such that their contraction facilitates pupillary dilation (mydriasis). The dilator pupillae muscle receives innervation from the sympathetic nervous system.

Gross anatomy

The dilator pupillae muscle is a circumferential, spoke-like arrangement of contractile myoepithelial cells located in the mid-periphery of the posterior leaf of the iris, anterior to the pigmented epithelium. Like the sphincter pupillae muscle, it is located posterior to the rich connective tissue stroma and neurovasculature of the anterior iris leaf 

Innervation

The dilator pupillae muscle is innervated by the sympathetic nervous system. Postganglionic sympathetic fibers project from the superior cervical ganglion to join the carotid plexus. These fibers then course with the ophthalmic artery, forming a number of long ciliary nerves that supply the dilator pupillae muscle

Action

Contraction of the dilator pupillae muscle facilitates dilation of the pupil (mydriasis). This increases the amount of light impinging on the retina

Clinical importance

• alongside endogenous sympathetic stimulation, sympathomimetic drugs (e.g. stimulants) may act on the dilator pupillae muscle, resulting in mydriasis

• prolonged significant mydriasis narrows the iridocorneal angle for aqueous humor drainage, increasing the risk of closed angle glaucoma

• the miosis seen in patients with Horner syndrome is mediated by inactivation of the dilator pupillae muscle due to a lesion interrupting sympathetic outflow