# Lecture 16: Clinical Anatomy of the Pelvis and Head/Neck ## Unit 1.5: Human Gross Anatomy III - Pelvis and Head/Neck --- ## Learning Objectives By the end of this lecture, students will be able to: 1. Apply anatomical knowledge to physical examination of the pelvis and head/neck 2. Describe the anatomical basis for common clinical procedures 3. Explain surface anatomy landmarks for the head and neck 4. Correlate anatomical structures with common imaging findings 5. Apply anatomical knowledge to understand referred pain patterns 6. Integrate pelvic and head/neck anatomy for clinical reasoning --- ## Physical Examination of the Pelvis Physical examination of the pelvic region requires understanding of the underlying anatomy to interpret findings and perform procedures safely. In examining the male genitalia, the penis is inspected for lesions and the foreskin assessed for retractability (phimosis is inability to retract). The urethral meatus is examined for position (hypospadias if on the ventral surface, epispadias if dorsal) and discharge. The scrotum is palpated for swelling; transillumination helps distinguish fluid collections (hydrocele) from solid masses. Each testis is palpated for size, consistency, and masses, with the normal testis feeling smooth and rubbery. The epididymis is felt posterolateral to the testis; tenderness suggests epididymitis. The spermatic cord is palpated for the presence of varicocele (described as feeling like a "bag of worms" and more prominent with standing or Valsalva maneuver). In examining the female external genitalia, the vulva is inspected for skin changes, lesions, and discharge. The labia are examined for swelling, particularly at the posterolateral aspect where Bartholin's gland cysts may occur. The urethral meatus is identified above the vaginal orifice. Vaginal prolapse may be visible at the introitus. The digital rectal examination (DRE) is fundamental for assessing pelvic structures in both sexes. Anal sphincter tone is assessed as the finger enters. In males, the prostate gland is felt anteriorly as a bilobed structure with a midline sulcus; its size, consistency, and presence of nodules are assessed. The normal prostate is approximately walnut-sized, smooth, and rubbery. Prostate cancer typically arises in the peripheral zone, which is accessible to DRE. In females, the cervix may be palpable through the anterior rectal wall. The rectovaginal septum and pouch of Douglas can be assessed rectovaginally. In both sexes, the rectal mucosa is palpated for masses, and stool is examined for blood. Pelvic examination in females includes speculum examination to visualize the cervix and vaginal walls, and bimanual examination to assess the uterus (size, position, mobility, tenderness) and adnexa (ovaries and fallopian tubes). Panel A: Male scrotal examination demonstrating palpation of testis and epididymis with transillumination technique for hydrocele. Panel B: Digital rectal examination in male showing prostate gland palpation with normal anatomical relationships. Panel C: Bimanual pelvic examination in female showing assessment of uterus between abdominal and vaginal hands with ovary lateral to uterus. Panel D: Comparison of normal findings versus common abnormalities detected on examination. --- ## Physical Examination of the Head and Neck Head examination encompasses multiple systems and cranial nerves. Visual acuity is tested with a Snellen chart. Pupillary reactions are assessed for size, equality, and response to light (direct and consensual) and accommodation. Eye movements are tested in an H-pattern to assess cranial nerves III, IV, and VI. Visual fields are tested by confrontation. Fundoscopy examines the optic disc for papilledema (indicating raised intracranial pressure), cup-to-disc ratio (increased in glaucoma), and vascular changes. Examination of the ears includes inspection of the external canal and tympanic membrane with an otoscope. Hearing is tested with the whispered voice test (examiner whispers numbers at arm's length from one ear while masking the other), the Rinne test (comparing air conduction to bone conduction with a tuning fork), and the Weber test (placing a tuning fork on the vertex to detect lateralization, which occurs toward the affected ear in conductive loss and away from it in sensorineural loss). The nose is examined for septal deviation, mucosal changes, and polyps. Sinus tenderness is assessed by palpation over the frontal sinuses (above the medial eyebrow) and maxillary sinuses (over the cheeks). The oral cavity is examined systematically: the lips, buccal mucosa, gums, teeth, tongue (dorsum, ventral surface, lateral edges), palate (hard and soft), tonsils, and posterior pharynx. Tongue movement is tested by asking the patient to protrude and move the tongue side to side (CN XII). Palatal movement is observed by asking the patient to say "ah" (CN IX, X). Neck examination begins with inspection for masses, asymmetry, and thyroid enlargement. Lymph nodes are palpated systematically, including the submental, submandibular, preauricular, postauricular, occipital, anterior cervical, posterior cervical, and supraclavicular groups. The thyroid is examined by standing behind the patient and palpating while the patient swallows water; each lobe and the isthmus are assessed for size, nodules, and tenderness. Tracheal position is verified at the sternal notch. The carotid pulse is palpated gently (not simultaneously on both sides), and the carotid is auscultated for bruits, which suggest turbulent flow from stenosis. Panel A: Eye examination showing pupillary light reflex testing and H-pattern for eye movements. Panel B: Tuning fork tests -- Weber (fork on vertex) and Rinne (comparing air and bone conduction). Panel C: Lymph node palpation sequence showing submental, submandibular, cervical chain, and supraclavicular groups. Panel D: Thyroid examination from behind with patient swallowing, showing bimanual technique. --- ## Surface Anatomy Landmarks Surface anatomy landmarks serve as reference points for underlying structures and guide clinical procedures. Skull landmarks include the nasion (depression at the bridge of the nose, overlying the anterior cranial fossa), the glabella (smooth prominence between the eyebrows), the vertex (highest point of the skull), the inion (external occipital protuberance, palpable at the back of the head), and the mastoid process (bony prominence behind the ear, containing mastoid air cells that may become infected). The pterion, at the temple, is the thinnest part of the skull and overlies the middle meningeal artery; it is not directly palpable but its location is important clinically. Facial landmarks include three foramina that align vertically in the same sagittal plane: the supraorbital notch or foramen (at the junction of the medial and middle thirds of the supraorbital margin, transmitting the supraorbital nerve from V1), the infraorbital foramen (approximately 1 cm below the orbital margin in the maxilla, transmitting the infraorbital nerve from V2), and the mental foramen (on the mandible below the second premolar, transmitting the mental nerve from V3). These landmarks guide nerve blocks for facial anesthesia. Neck landmarks relate to cervical vertebral levels. The hyoid bone is at the level of C3 and marks the junction between the floor of the mouth and the neck; it is the only bone not articulating with any other. The thyroid cartilage (Adam's apple) is at C4-C5; its superior border is level with the carotid bifurcation. The cricoid cartilage is at C6, marking the junction between the larynx and trachea, the pharynx and esophagus, and the level where the inferior thyroid artery and recurrent laryngeal nerve enter the larynx. The cricothyroid membrane lies between the thyroid and cricoid cartilages and is the site for emergency surgical airway. The sternal notch is at the level of T2-T3 and serves as a landmark for central venous catheter placement. Panel A: Lateral skull showing pterion region (highlighted), mastoid process, and external occipital protuberance (inion). Panel B: Face showing vertical alignment of supraorbital, infraorbital, and mental foramina with their nerve territories. Panel C: Anterior neck showing vertebral levels -- hyoid at C3, thyroid cartilage at C4-5, cricoid cartilage at C6, and cricothyroid membrane location. Panel D: Sternal notch at T2-3 level with adjacent surface landmarks for clinical reference. --- ## Pelvic Procedures Urinary catheterization requires understanding of urethral anatomy. The male urethra is approximately 20 cm long and has three curves and three narrowings. It passes through the prostate (prostatic urethra), the urogenital diaphragm (membranous urethra, the narrowest portion), and the corpus spongiosum (spongy urethra) to the external meatus. The catheter is passed with the penis held perpendicular to the body to straighten the curves. Resistance may be encountered at the membranous urethra (where the external sphincter lies) and at the prostatic urethra (particularly in men with prostatic enlargement). The female urethra is only about 4 cm long and runs a straight course from the bladder to the urethral meatus, which lies anterior to the vaginal opening. Catheterization is generally straightforward once the meatus is visualized. Paracentesis (abdominal tap) is performed to sample or drain ascitic fluid. The preferred site is in the left lower quadrant, approximately 2-3 cm medial and superior to the anterior superior iliac spine. This location avoids the cecum (which is on the right), the bladder (which should be emptied first), and the inferior epigastric vessels (which run in the rectus sheath medially). Ultrasound guidance confirms the presence and location of fluid. Lumbar puncture (spinal tap) obtains cerebrospinal fluid from the subarachnoid space. The procedure is performed at the L3-L4 or L4-L5 interspace, below the level where the spinal cord terminates (typically at L1-L2 in adults). The iliac crest line (a line connecting the highest points of the iliac crests) crosses the spine at the L4 spinous process, providing a surface landmark. The needle passes through skin, subcutaneous tissue, supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, dura mater, and arachnoid mater before entering the subarachnoid space containing CSF. Culdocentesis involves inserting a needle through the posterior vaginal fornix to access the rectouterine pouch (pouch of Douglas), the lowest point of the peritoneal cavity in the upright female. It may be used to detect hemoperitoneum (as in ruptured ectopic pregnancy) or to drain pelvic abscesses. Panel A: Male urethral anatomy showing prostatic, membranous, and spongy portions with catheter course and points of resistance. Panel B: Paracentesis site in left lower quadrant showing relationship to anterior superior iliac spine and structures to avoid (cecum, bladder, inferior epigastric vessels). Panel C: Lumbar puncture showing patient position, iliac crest line at L4, and needle trajectory through spinal ligaments to subarachnoid space. Panel D: Culdocentesis showing needle through posterior fornix into the pouch of Douglas. --- ## Head and Neck Procedures Cricothyrotomy is an emergency surgical airway performed when orotracheal intubation is impossible ("can't intubate, can't ventilate" scenario). A horizontal incision is made through the skin and the cricothyroid membrane, which lies between the thyroid and cricoid cartilages. The membrane is approximately 9 mm in height and is relatively avascular, lying in a subcutaneous position. An endotracheal or tracheostomy tube is inserted into the trachea through this opening. This procedure is faster than tracheostomy but is considered a temporary measure. Tracheostomy creates an opening in the anterior tracheal wall, usually between the second and fourth tracheal rings. The thyroid isthmus overlies rings 2-4 and must be divided or retracted. A tracheostomy tube is inserted for long-term airway management. Indications include prolonged mechanical ventilation, upper airway obstruction, and airway protection in patients at risk for aspiration. Complications include hemorrhage (from thyroid vessels or, rarely, the innominate artery), pneumothorax, and injury to the recurrent laryngeal nerves. Central venous catheterization in the neck provides access for medication administration, hemodynamic monitoring, and hemodialysis. The internal jugular vein is approached with the patient in Trendelenburg position (head down, to distend the vein and reduce air embolism risk). Landmarks include the triangle between the two heads of the sternocleidomastoid muscle; the carotid pulse is palpated to identify the medial boundary. Ultrasound guidance is standard of care. The vein is compressible (the artery is not) and lies lateral to the carotid artery. The subclavian vein is approached below the clavicle, aiming toward the sternal notch; it lies anterior and inferior to the subclavian artery, separated by the anterior scalene muscle. Complications include arterial puncture, pneumothorax, hemothorax, and air embolism. Thyroid surgery is approached through a transverse collar incision. The strap muscles are divided or retracted to expose the gland. Critical structures to identify and preserve include the recurrent laryngeal nerve (ascending in the tracheoesophageal groove), the external branch of the superior laryngeal nerve (running with the superior thyroid artery to the cricothyroid muscle), and the parathyroid glands (on the posterior surface of the thyroid lobes). Complications include vocal cord paralysis (from recurrent or superior laryngeal nerve injury), hypocalcemia (from parathyroid damage), and hemorrhage. Panel A: Cricothyrotomy showing incision site through cricothyroid membrane between thyroid and cricoid cartilages. Panel B: Tracheostomy showing incision between tracheal rings 2-4 and relationship to thyroid isthmus. Panel C: Internal jugular vein cannulation showing ultrasound probe position, vein lateral to carotid artery, and needle trajectory. Panel D: Thyroid surgery exposure showing recurrent laryngeal nerve in tracheoesophageal groove and parathyroid glands on posterior thyroid surface. --- ## Imaging of the Pelvis Pelvic imaging modalities are selected based on the clinical question. Plain radiographs (X-rays) are useful for evaluating pelvic fractures, hip joint abnormalities (osteoarthritis, avascular necrosis), and radiopaque calcifications (bladder stones, ureteric stones, phleboliths). Computed tomography (CT) provides excellent bony detail and is the primary modality for trauma evaluation (detecting fractures and associated hemorrhage). With contrast, it identifies vascular injuries, tumors, and lymphadenopathy. CT is also used for acute abdominal and pelvic conditions such as appendicitis, diverticulitis, and bowel obstruction. Magnetic resonance imaging (MRI) offers superior soft tissue contrast without ionizing radiation. It is the modality of choice for staging rectal cancer, evaluating prostate cancer, and assessing gynecological conditions including endometriosis, uterine fibroids, and ovarian masses. MRI is also valuable for evaluating the pelvic floor and ligaments. Ultrasound is the first-line imaging modality in pregnancy for fetal assessment. Transabdominal and transvaginal approaches are used for gynecological evaluation (ovarian cysts, ectopic pregnancy, uterine pathology). Transrectal ultrasound guides prostate biopsy. Pelvic ultrasound can assess bladder volume and detect hydronephrosis. Panel A: Pelvic X-ray showing normal bony anatomy with hip joints and sacroiliac joints. Panel B: CT pelvis with contrast showing bladder, rectum, and pelvic vessels with lymph nodes. Panel C: MRI pelvis (T2-weighted) showing superior soft tissue detail of uterus, ovaries, and pelvic floor. Panel D: Transvaginal ultrasound showing uterus and ovary with follicle. --- ## Imaging of the Head and Neck Plain radiographs of the cervical spine assess alignment and may detect fractures, though CT has largely replaced them for trauma evaluation. Soft tissue neck radiographs can identify epiglottitis (thumbprint sign), retropharyngeal abscess (prevertebral soft tissue widening), and foreign bodies. CT of the head is the first-line imaging for acute stroke (to rule out hemorrhage before thrombolysis), head trauma (detecting skull fractures, intracranial hemorrhage, and brain contusions), and evaluation of acute altered mental status. CT with bone windows is excellent for skull base fractures. CT angiography evaluates the cerebral and carotid vasculature. CT of the neck with contrast is used for evaluating neck masses, lymphadenopathy, and infections (abscesses). It provides excellent detail of the airway and can detect vascular involvement by tumors. MRI of the brain provides superior soft tissue contrast for evaluating tumors, demyelinating diseases, and ischemic stroke (particularly with diffusion-weighted imaging for acute infarction). MRI of the neck is useful for brachial plexus evaluation and soft tissue tumor characterization. Ultrasound of the neck is the primary modality for evaluating thyroid nodules (assessing size, composition, and features concerning for malignancy) and guides fine needle aspiration biopsy. Carotid Doppler ultrasound evaluates for carotid artery stenosis by measuring flow velocities. Lymph nodes can be characterized and biopsied under ultrasound guidance. Panel A: CT head showing normal anatomy with ventricles, gray-white differentiation, and skull. Panel B: CT head with acute epidural hematoma (lens-shaped) compared to subdural hematoma (crescent-shaped). Panel C: MRI brain (T1-weighted with contrast) showing enhanced tumor. Panel D: Thyroid ultrasound showing nodule with characteristic features annotated. --- ## Referred Pain Patterns Referred pain occurs when pain from a visceral organ is perceived as arising from a somatic structure that shares the same spinal cord segments. Understanding referred pain patterns helps interpret patient symptoms in terms of underlying anatomy. In the pelvis, bladder pain is typically perceived in the suprapubic region and perineum (T11-L2 segments). Prostatic pain refers to the perineum and lower back (S2-S4). Uterine body pain refers to the lower abdomen and lower back (T10-L1), while cervical pain refers to the lower back and thighs (S2-S4). Ovarian pain refers to the lower abdomen on the ipsilateral side (T10-L1). Rectal pain refers to the sacrum and perineum (S2-S4). Notably, ovarian torsion or ruptured ovarian cyst may cause pain that mimics appendicitis or renal colic. In the head and neck, cardiac pain classically refers to the left arm, jaw, and neck (T1-T4 dermatomes). Central diaphragmatic irritation refers pain to the shoulder (C3-C5, via the phrenic nerve); this explains shoulder pain in subphrenic abscess, ruptured spleen, or ruptured ectopic pregnancy with hemoperitoneum irritating the diaphragm. Ear pain (otalgia) may be referred from the throat (via CN IX), teeth (via V3), or temporomandibular joint (via V3), explaining why ear examination may be normal in patients with ear pain from pharyngitis or dental disease. Conversely, pain from the ear (via CN V, VII, IX, X) may refer to the throat. Panel A: Pelvic organs with their referred pain territories marked on body surface -- bladder to suprapubic, uterus to lower abdomen, and ovary to ipsilateral lower quadrant. Panel B: Cardiac referred pain pattern to left arm, jaw, and neck. Panel C: Diaphragmatic referred pain to shoulder via phrenic nerve (C3-5). Panel D: Ear-throat referred pain connections via shared cranial nerve innervation (V, IX, X). --- ## Common Clinical Scenarios Ectopic pregnancy occurs when a fertilized ovum implants outside the uterine cavity, most commonly in the ampulla of the fallopian tube. It presents with lower abdominal pain (often unilateral) and vaginal bleeding in a woman of reproductive age with a positive pregnancy test. Rupture causes intraperitoneal hemorrhage, potentially leading to hemodynamic instability. Shoulder pain may occur from diaphragmatic irritation by blood in the peritoneal cavity. Transvaginal ultrasound may show an adnexal mass or free fluid; an empty uterus with elevated beta-hCG is suspicious for ectopic pregnancy. Testicular torsion is a urological emergency in which the spermatic cord twists, compromising blood flow to the testis. It typically presents in adolescents with sudden, severe testicular pain, often with nausea. On examination, the testis is high-riding (due to cord shortening with twisting) and the cremasteric reflex is absent. The testis becomes nonviable within approximately six hours, making rapid diagnosis and surgical detorsion essential. Doppler ultrasound showing absent blood flow confirms the diagnosis. Appendicitis classically presents with periumbilical pain that later localizes to the right lower quadrant. The initial visceral pain (T10 dermatome) reflects inflammation of the appendix before it involves the parietal peritoneum; once parietal peritoneal irritation occurs, pain localizes to McBurney's point (one-third of the distance from the anterior superior iliac spine to the umbilicus). The psoas sign (pain with hip extension, when the appendix lies retroperitoneally on the psoas) and obturator sign (pain with internal rotation of the flexed hip, when the appendix lies near the obturator internus) may be present. In stroke and transient ischemic attack (TIA), carotid territory ischemia (from the anterior circulation) produces contralateral hemiparesis, hemisensory loss, and (if the dominant hemisphere is affected) aphasia. Vertebrobasilar territory ischemia (from the posterior circulation) produces vertigo, ataxia, diplopia, dysarthria, and visual field defects. A carotid bruit on examination may indicate stenosis, though its absence does not exclude disease. The distinction between Bell's palsy (peripheral CN VII palsy) and stroke is clinically important. In Bell's palsy, the entire ipsilateral face is weak, including the forehead, because the facial nerve supplies all muscles. In stroke, the forehead is spared because the frontalis muscle receives bilateral upper motor neuron innervation; only the lower face is weak on the side contralateral to the lesion. Panel A: Ectopic pregnancy showing tubal location with rupture and shoulder pain from diaphragmatic irritation. Panel B: Testicular torsion showing twisted spermatic cord, high-riding testis, and absent cremasteric reflex. Panel C: Appendicitis showing pain progression from periumbilical to McBurney's point with psoas and obturator sign maneuvers. Panel D: Comparison of Bell's palsy (entire face including forehead) versus stroke (forehead spared) facial weakness patterns. --- ## Anatomical Pearls for Clinical Practice Several anatomical relationships are particularly important for avoiding complications and understanding clinical presentations. In pelvic surgery, the relationship of the ureter to the uterine artery is critical: "water under the bridge" reminds us that the ureter passes beneath the uterine artery at the level of the cervix, approximately 2 cm lateral to the cervix. The ureter is vulnerable to injury during hysterectomy at this location. The left gonadal vein drains into the left renal vein (while the right drains directly into the IVC), explaining why left-sided varicocele is more common (due to increased hydrostatic pressure) and may suggest left renal vein compression or obstruction. Prostate cancer most commonly arises in the peripheral zone of the prostate, which is the portion accessible to digital rectal examination. Early detection by DRE is therefore possible before the cancer has extended beyond the prostatic capsule. The pudendal nerve passes around the ischial spine, a landmark that guides pudendal nerve block for perineal anesthesia (used in obstetric procedures). In head and neck surgery, the recurrent laryngeal nerve lies in the tracheoesophageal groove and is closely related to the inferior thyroid artery. It must be identified and preserved during thyroidectomy to prevent vocal cord paralysis. The facial nerve traverses the parotid gland, dividing it into superficial and deep lobes. During parotidectomy, the nerve must be meticulously identified and preserved to avoid facial paralysis. The spinal accessory nerve crosses the posterior triangle superficially and is vulnerable during lymph node biopsy in this region. Injury causes shoulder droop and weakness of head turning. The carotid bifurcation is at the level of the upper border of the thyroid cartilage (C4), approximately at the angle of the mandible. This landmark is useful for locating the carotid pulse and for carotid endarterectomy. Panel A: "Water under the bridge" -- ureter passing beneath uterine artery near cervix with zone of surgical vulnerability. Panel B: Left gonadal vein draining to left renal vein versus right draining to IVC. Panel C: Facial nerve course through parotid with five terminal branches to be preserved. Panel D: Recurrent laryngeal nerve relationship to inferior thyroid artery and tracheoesophageal groove. --- ## Summary Physical examination of the pelvis and head/neck requires systematic approach and understanding of underlying anatomy. Digital rectal examination assesses anal tone, prostate (in males), and rectal contents. Cranial nerve examination proceeds systematically through all twelve nerves. Surface landmarks guide clinical procedures: the cricoid cartilage at C6 marks the site of the cricothyroid membrane for emergency airway access, and the carotid bifurcation at C4 is at the level of the thyroid cartilage. Pelvic procedures include urinary catheterization (navigating the longer male urethra), paracentesis (in the left lower quadrant), lumbar puncture (at L3-4 or L4-5), and culdocentesis (through the posterior fornix). Head and neck procedures include cricothyrotomy, tracheostomy, central venous catheterization, and thyroid surgery. Imaging modality selection is based on the clinical question: CT for acute evaluation, MRI for soft tissue detail, ultrasound for thyroid and pregnancy. Referred pain patterns follow dermatomal innervation: diaphragmatic pain refers to the shoulder (C3-5), while pelvic organ pain refers to lower abdominal and back territories. Common clinical scenarios (ectopic pregnancy, testicular torsion, appendicitis, stroke vs Bell's palsy) integrate anatomical knowledge with clinical reasoning. --- ## Key Terms | Term | Definition | |------|------------| | McBurney's point | Surface landmark for the base of the appendix, located one-third of the distance from the anterior superior iliac spine to the umbilicus | | Cricothyroid membrane | Site of emergency surgical airway, located between the thyroid and cricoid cartilages | | Pouch of Douglas | Rectouterine pouch; the lowest point of the peritoneal cavity in females, accessed via culdocentesis | | Carotid bifurcation | Division of the common carotid into internal and external carotid arteries at the level of C4, corresponding to the upper border of the thyroid cartilage | | Pudendal nerve block | Regional anesthesia technique performed at the ischial spine for perineal procedures | | Trendelenburg position | Head-down positioning used during internal jugular vein cannulation to distend the vein and reduce air embolism risk | --- *This content is subject to the [MIT License](https://opensource.org/licenses/MIT). © 2024–2026 Hibbert School of Medicine.*