Pelvic Vessels — Logic-Based Notes (Zero Omission)

1️⃣ Big Picture Logic

🔑 Core principle

• Pelvic walls + pelvic viscera are supplied by:
• Internal iliac artery
• Drained by internal iliac vein
• Vessels lie within parietal pelvic fascia
• Only branches leaving the pelvis need to pierce this fascia

➜ Exception: obturator vessels (they leave via obturator canal)

👉 Why this matters

• Explains:
• Surgical planes
• Bleeding patterns
• Retroperitoneal haemorrhage in pelvic fractures

2️⃣ Internal Iliac Artery — Origin & Division

📍 Origin

• Common iliac artery bifurcates
• At pelvic brim
• Opposite sacroiliac joint

🔀 Course

• Internal iliac artery:
• Passes downwards
• Quickly divides into:
• Posterior division (short)
• Anterior division (long)

3️⃣ Posterior Division — Parietal Supply Only

🔢 Branches (3 total)

All are parietal

1. Iliolumbar
2. Lateral sacral
3. Superior gluteal

🟢 Iliolumbar Artery

Course

• Passes upwards out of pelvis
• Relations:
• In front of lumbosacral trunk
• Behind obturator nerve
• Deep to psoas major

Branches

A. Lumbar branch

• Represents 5th lumbar segmental artery
• Supplies:
• Psoas
• Quadratus lumborum
• Erector spinae (via posterior branch)
• Gives spinal branch through foramen between L5 & sacrum

B. Iliac branch

• Supplies:
• Iliacus muscle
• Iliac bone
• Contributes to anastomosis around ASIS:
• Deep circumflex iliac
• Superficial circumflex iliac
• Ascending branch of lateral circumflex femoral
• Upper branch of deep division of superior gluteal

🟢 Lateral Sacral Artery

• Often double
• Runs downwards lateral to anterior sacral foramina
• Lies in front of sacral plexus roots

Pelvic supply

• Roots of sacral plexus
• Piriformis muscle

Spinal branches

• Enter anterior sacral foramina
• Supply:
• Spinal meninges
• Nerve roots
• Exit via posterior sacral foramina
• Supply muscles over back of sacrum

Segmental logic

• Replaces lumbar segmental arteries
• Usually:
• Superior sacral artery → S1–S2
• Inferior sacral artery → remaining sacral segments

🟢 Superior Gluteal Artery

• Largest branch of internal iliac artery
• Pierces pelvic fascia:
• Usually between lumbosacral trunk & S1 nerve
• Exits pelvis via:
• Greater sciatic foramen
• Above piriformis

👉 Buttock course & distribution considered separately

Pelvic Vessels — Internal Iliac Artery (POSTERIOR DIVISION) — SINGLE MASTER TABLE

4️⃣ Anterior Division — Visceral + Parietal Supply

🔢 Usual branches (9 total)

A. Bladder-related (3)

1. Superior vesical
2. Obliterated umbilical
3. Inferior vesical

B. Other visceral (3)

1. Middle rectal
2. Uterine
3. Vaginal

C. Parietal (3)

1. Obturator
2. Internal pudendal
3. Inferior gluteal

➡️ Terminal branches

• Internal pudendal
• Inferior gluteal

5️⃣ Key Branches — Anterior Division

🔵 Superior Vesical Artery

• Persistent proximal part of fetal umbilical artery
• Distal part → obliterated
• Forms medial umbilical ligament
• Appears as direct continuation

Course

• Runs along pelvic side wall
• Turns medially to upper bladder

Supply

• Upper bladder
• Adjacent:
• Ureter
• Vas deferens

🔵 Inferior Vesical Artery (Male)

• Arises lower than superior vesical
• Runs medially across pelvic floor

Supplies

• Trigone
• Lower bladder
• Ureter
• Vas deferens
• Seminal vesicle
• Prostate

🔵 Middle Rectal Artery

• Frequently:
• Absent
• Or small
• When absent:
• Rectal muscle supply replaced by:
• Prostatic branches (male)
• Vaginal branches (female)

🔵 Uterine Artery

Course (VERY IMPORTANT)

• Crosses pelvis in base of broad ligament
• Passes above ureter

👉 “Water under the bridge”

• At cervix:
• Turns upwards
• Closely applied to uterine muscle
• Runs in broad ligament

Termination

• At uterine tube entrance:
• Turns laterally
• Supplies tube
• Anastomoses with tubal branch of ovarian artery

🔵 Vaginal Artery

• Supplies upper vagina
• Female equivalent of inferior vesical artery
• May arise from uterine artery

🔵 Obturator Artery

Course

• Runs along pelvic side wall
• Lies below obturator nerve
• Exits pelvis via obturator foramen
• With nerve & vein

Branch

• Pubic branch:
• Supplies periosteum of pubis
• Anastomoses with pubic branch of inferior epigastric artery

⚠️ Clinical: Abnormal Obturator Artery

• Seen in ~30%
• Anastomosis enlarges
• Replaces normal obturator artery
• Usually passes:
• Lateral to femoral ring
• Near external iliac vein

⚠️ Danger

• If artery runs medial to femoral ring
• Near lacunar ligament
• At risk during femoral hernia surgery

🔵 Inferior Gluteal Artery

• Runs backward through pelvic fascia
• Passes:
• Below S1 nerve (sometimes S2)
• Exits via:
• Greater sciatic foramen
• Below piriformis

🔵 Internal Pudendal Artery

• Lies anterior to inferior gluteal
• Pierces pelvic fascia
• Exits via:
• Greater sciatic foramen
• Below piriformis
• Supplies:
• Perineum
• Anal region
• External genitalia

6️⃣ Internal Iliac Vein

📍 Formation

• Wide vessel (~3 cm long)
• Begins above greater sciatic notch
• Formed by:
• Gluteal veins
• Veins accompanying internal iliac branches

Course

• Ascends posteromedial to artery
• Joins external iliac vein
• Forms common iliac vein

🩸 Tributaries

• Correspond to arterial branches
• Also receives plexus drainage from:
• Rectal
• Vesical
• Prostatic
• Uterine
• Vaginal venous plexuses

7️⃣ Clinical Logic of Pelvic Veins

❗ Retroperitoneal Haemorrhage

• Pelvic veins:
• Large
• Valveless
• Sub-peritoneal
• Pelvic fractures → severe hidden bleeding

🔁 Vertebral Venous Plexus Communication

• Via lateral sacral veins
• Internal iliac vein ↔ vertebral venous plexuses

⚠️ No valves in pelvic veins

🧠 Pressure Bypass Logic

• Sudden ↑ abdominal pressure (coughing):
• IVC capacity exceeded
• Blood flows:
• Backwards into vertebral venous plexus
• Into posterior intercostal veins
• Via azygos system → SVC
• Diaphragm bypassed

🎯 Metastatic Spread

• Pelvic organ cancers:
• Can spread to vertebrae
• Via retrograde venous flow
• Explains:
• Vertebral secondaries from pelvic primaries

🟥 TABLE 1 — Anterior Division: Overview & Branch Classification

🟦 TABLE 2 — Bladder-Related Branches (Anterior Division)

🟩 TABLE 3 — Other Visceral Branches

🟨 TABLE 4 — Parietal Branches (Pelvic Wall & Exit Routes)

⚠️ TABLE 5 — Obturator Artery: Variant & Surgical Danger

🟪 TABLE 6 — Internal Iliac Vein: Formation & Drainage

🟥 TABLE 7 — Pelvic Venous Plexuses & Properties

🧠 TABLE 8 — Pressure Bypass & Metastatic Logic (HIGH-YIELD)

Pelvic Nerves — Logic-based notes

1️⃣ Obturator nerve — “pelvic side-wall → obturator canal → adductor thigh”

Origin (why it’s lumbar plexus)

• Obturator nerve = branch of lumbar plexus
• Formed within psoas major
• From anterior divisions (anterior rami) of L2, L3, L4

Main functional identity

• Nerve of the adductor compartment of the thigh

Pelvic course (stepwise)

1. Emerges by piercing medial border of psoas
2. Passes straight along side wall of pelvis to obturator foramen
3. Crosses pelvic brim medial to sacroiliac joint
• i.e. runs on ala of sacrum
4. Runs forward between:
• internal iliac vessels
• and fascia on obturator internus

Ovary relation → referred pain logic

• Anterior to internal iliac vessels, obturator nerve is separated from normally situated ovary only by:
• parietal peritoneum lining pelvic wall
• Therefore:
• Ovarian pain → referred along obturator nerve → medial thigh skin
• The text’s key nuance:
• This may be less irritation of the main nerve trunk
• and more irritation/inflammation of parietal peritoneum
• because that peritoneum here is supplied by obturator nerve

Obturator canal/foramen arrangement (high-yield order)

• Obturator artery + vein converge to obturator foramen
• In the foramen:
• nerve lies highest (against pubic bone)
• artery below nerve
• vein below artery
• (so: N–A–V, top → bottom)

Division within foramen

• Nerve divides in the foramen into:
• Anterior division
• passes anterior to upper border of obturator externus
• Posterior division
• pierces obturator externus
• after giving a branch to supply obturator externus
• (Further thigh distribution referenced elsewhere in your source)

Accessory obturator nerve (variant)

• Occasionally present
• Also emerges from medial border of psoas
• But travels differently:
• Like femoral nerve, passes over superior pubic ramus to thigh
• Supplies:
• pectineus

2️⃣ Sacral plexus — “lumbosacral trunk + S1–S4 → nerves of lower limb & pelvis”

Why sacral plexus exists (inputs)

• Not all lumbar nerves are used up in lumbar plexus:
• part of L4 + all of L5 anterior rami enter sacral plexus

Lumbosacral trunk formation

• After L4 gives off branches to lumbar plexus:
• L4 emerges from medial border of psoas
• joins anterior ramus of L5
• → forms lumbosacral trunk

Lumbosacral trunk course & relations

• Passes over ala of sacrum
• Crosses pelvic brim medial to obturator nerve
• Separated from obturator nerve by:
• iliolumbar artery and veins

Completion of plexus

• Lumbosacral trunk descends to join:
• anterior rami of upper four sacral nerves (S1–S4)
• → Sacral plexus formed

3️⃣ Sacral plexus — shape, position, coverings, neighbors

Shape + position

• Broad triangular structure
• Formed by junction of nerves lateral to anterior sacral foramina
• Rests on piriformis
• Covered anteriorly by parietal pelvic fascia investing piriformis

What lies in front of it (layer logic)

• Anterior to fascia:
• lateral sacral arteries and veins lie in front of sacral nerves
• At higher level:
• common iliac vessels lie over the lumbosacral trunk
• Gluteal vessels relationship:
• Superior gluteal artery usually passes backwards above S1
• Inferior gluteal artery usually passes backwards below S1
• (variant: they may pass above and below S2 instead)
• Ureter:
• lies in front of internal iliac vessels
• is well anterior to upper part of plexus
• Most anterior:
• parietal pelvic peritoneum and pelvic viscera

Autonomic link

• Sacral nerves receive grey rami communicantes
• from sacral sympathetic ganglia

4️⃣ Plexus “division logic” → how limb compartments get innervation

Key organisational principle

• Sacral nerves give off certain branches, then divide:
• into anterior divisions and posterior divisions
• Lumbosacral trunk also divides similarly
• These divisions then branch and reunite
• Result: nerves supplying flexor and extensor compartments of lower limb

5️⃣ Named branches from sacral plexus (from your text, zero omission)

A) Nerve to piriformis

• Piriformis supplied by separate twigs
• From posterior divisions of S1 and S2

B) Perforating cutaneous nerve

• From posterior divisions of S2 and S3
• Pierces sacrotuberous ligament
• Curves round lower border of gluteus maximus
• Supplies skin of buttock

C) Posterior femoral cutaneous nerve

• Formed by branches from:
• posterior divisions of S1 and S2
• anterior divisions of S2 and S3
• Course:
• passes backwards below piriformis
• behind sciatic nerve
• sciatic nerve separates it from ischium
• Enters gluteal region

D) Superior gluteal nerve

• From posterior divisions of L4, L5, S1
• Leaves pelvis above piriformis

E) Inferior gluteal nerve

• From posterior divisions of L5, S1, S2
• Leaves pelvis below lower border of piriformis

F) Coccygeal plexus

• Minor mingling of:
• branch from S4
• S5
• coccygeal nerve
• Branches supply postanal skin over coccyx

6️⃣ Sciatic nerve formation + exit (and the important variant)

Two-component build

1) Tibial part

• Big branch formed by union of branches from all five anterior divisions:
• L4, L5, S1–S3

2) Common peroneal (common fibular) part

• Formed by union of branches from posterior divisions:
• L4, L5, S1, S2

Usual joining

• Usually the two join in the pelvis
• Sciatic nerve leaves pelvis:
• below lower border of piriformis
• lying on ischium
• lateral to ischial spine

Variant

• If the two components do not join in pelvis:
• common peroneal part pierces lower part of piriformis as it leaves pelvis

7️⃣ Nerve to obturator internus

• From anterior divisions of L5, S1, S2
• Also supplies superior gemellus
• Leaves pelvis:
• lateral to pudendal vessels
• below piriformis

8️⃣ Nerve to quadratus femoris

• From anterior divisions of L4, L5, S1
• Also supplies:
• inferior gemellus
• hip joint
• Leaves pelvis:
• in front of sciatic nerve
• sciatic nerve holds it down on ischium

9️⃣ Pudendal nerve — origin + pelvic exit route

Roots

• From anterior divisions of S2, S3, S4

Course

1. Passes back between piriformis and coccygeus
2. Lies medial to pudendal vessels
3. In buttock:
• appears between piriformis and sacrospinous ligament
• curls around sacrospinous ligament
4. Runs forward into ischioanal fossa

🔟 Levator ani / pelvic floor innervation (S3–S4 details)

Muscular branches (S3, S4)

• Supply on upper (pelvic) surfaces:
• pubococcygeus
• iliococcygeus
• and coccygeus

Perineal branch of S4

• Passes between coccygeus and levator ani
• Enters ischioanal fossa
• Supplies:
• puborectalis
• pubourethralis
• pubovaginalis
• perianal skin

1️⃣1️⃣ Pelvic splanchnic nerves (parasympathetic) — “nervi erigentes” but broader

Roots

• Parasympathetic pelvic splanchnic nerves arise by several rootlets from:
• anterior surfaces of S2 and S3
• often S4
• Contribution from S3 is usually the largest

Course + mixing

• Pass forward into inferior hypogastric plexuses
• Mix with sympathetic nerves
• Distributed to:
• pelvic viscera
• distal colon

Naming nuance

• Old term nervi erigentes is correct but incomplete
• They cause erection
• but also much more (as your text notes)

Pelvic Nerves — Master Logic Table (Zero Omission)

A. Obturator Nerve

B. Lumbosacral Trunk

C. Sacral Plexus — Structure & Relations

D. Plexus Division Logic

E. Posterior & Direct Branches of Sacral Plexus

F. Sciatic Nerve

G. Short Muscular Nerves

H. Pudendal Nerve

I. Pelvic Floor (Levator Ani) Innervation

J. Pelvic Splanchnic Nerves (Parasympathetic)

Sacral Sympathetic Trunks & Inferior Hypogastric Plexus — Logic-Based Notes

1️⃣ Sacral Sympathetic Trunks — position & purpose

📍 Course & position

• Sympathetic trunks cross the pelvic brim
• They pass behind the common iliac vessels
• Then descend in the concavity of the sacrum
• They lie along the medial margins of the anterior sacral foramina

🔢 Ganglia

• Each trunk usually has four sacral ganglia

🔻 Termination

• The two trunks converge anterior to the coccyx
• Unite to form a small midline swelling:
• Ganglion impar

2️⃣ Branches of the sacral sympathetic trunks

🟢 Somatic branches

• Distributed to all sacral nerves
• Therefore influence:
• Lower limb
• Perineum

🟢 Vascular branches

• Small filaments to:
• Lateral sacral vessels
• Median sacral vessels

🟢 Visceral branches

• Pass forward to join:
• Inferior hypogastric plexuses

3️⃣ Inferior Hypogastric Plexus — identity & location

🔑 Definition

• Inferior hypogastric plexus = major autonomic plexus
• One on each side wall of the pelvis

📍 Relations in the male

• Lateral to rectum
• Posterolateral to:
• Seminal vesicle
• Prostate
• Posterior part of bladder
• Middle of plexus lies:
• Level with
• Just behind the top of the seminal vesicle

📍 Relations in the female

• Lateral to:
• Rectum
• Cervix
• Vaginal fornix
• Posterolateral to bladder

🧠 Shape & size

• Rectangular, fenestrated plaque
• Contains nerves + ganglia
• Dimensions:
• ~5 cm anteroposteriorly
• ~2 cm vertically

4️⃣ Autonomic inputs to the inferior hypogastric plexus

🔵 Sympathetic components

Derived from:

1. Superior hypogastric plexus
• Via the hypogastric nerve
2. Sacral sympathetic ganglia

🟣 Parasympathetic components

• Preganglionic parasympathetic fibres
• From S2, S3, S4
• These are the pelvic splanchnic nerves

5️⃣ Relay logic inside the plexus

⚡ Sympathetic fibres

• About half of fibres in hypogastric nerves are:
• Myelinated
• Preganglionic
• These relay in ganglia of inferior hypogastric plexus
• Remaining sympathetic fibres:
• Pass through without relay

🌱 Parasympathetic fibres

• All parasympathetic fibres pass through plexus without relay
• They relay:
• In the walls of pelvic viscera

6️⃣ Visceral branches — neurovascular bundle logic

• Visceral branches of inferior hypogastric plexus:
• Accompany visceral branches & tributaries
• of internal iliac artery and vein
• Travel as neurovascular bundles

7️⃣ Organ-specific autonomic control (VERY HIGH-YIELD)

🟢 Parasympathetic (pelvic splanchnics)

Innervate:

• Detrusor muscle of bladder
• Muscle of rectum
• Colon from splenic flexure to rectum

Functions:

• Motor to emptying muscles
• Secretomotor to gut
• Vasodilator to erectile tissue of perineum

🔵 Sympathetic

Innervate smooth muscle of:

• Bladder neck
• Prostate
• Seminal vesicle
• Vas deferens
• Internal anal sphincter

Additional role:

• Facilitating function on uterine muscle

8️⃣ Sensory fibre pathways

🚽 Distension sensation

• Normal sensation of bladder and rectal distension
• Probably passes via:
• Pelvic splanchnic nerves

⚠️ Pain fibres

• Pain from pelvic viscera carried by:
• Both parasympathetic and sympathetic fibres

9️⃣ Pelvic parasympathetics & distal colon

• Pelvic splanchnic nerves also supply:
• Colon distal to splenic flexure
• Pathways:
• Ascend from inferior hypogastric plexus:
• To superior hypogastric plexus, or
• More often to its left side
• Then ascend:
• With branches of inferior mesenteric artery
• Or as independent retroperitoneal nerves

🔟 Final integrated logic (exam-lock)

• Parasympathetic (S2–S4):
• Emptying of bladder
• Peristalsis from splenic flexure → rectum
• Gut secretion
• Erectile vasodilation
• Sympathetic:
• Bladder neck contraction
• Internal anal sphincter tone
• Ejaculatory duct system (vas, seminal vesicle, prostate)
• Facilitates uterine contraction
• Inferior hypogastric plexus:
• Central mixing station
• Where pelvic autonomics redistribute to viscera

Sacral Sympathetic Trunks & Inferior Hypogastric Plexus — Master Table (Zero-Omission)