Cysts & Swellings of Skin and Subcutaneous Tissue
Surgery · General Surgery · lean revision notes
Cysts & Swellings of Skin and Subcutaneous Tissue
A bread-and-butter clinical surgery topic where examiners test your bedside reasoning: how you describe a swelling, the one sign that nails the diagnosis, and the surgical principle behind treatment. Most questions are image- or vignette-based, so anchor every lesion to a single discriminating feature.
Definition & basic vocabulary
A cyst is a fluid- or semisolid-filled cavity lined by epithelium (true cyst) or by compressed fibrous tissue (false/pseudocyst). A swelling is any abnormal localised enlargement. The classic six-point bedside description still wins marks: site, size, shape, surface, consistency, and relations (skin tethering, fixity to deep structures), plus fluctuation, transillumination, compressibility/reducibility, pulsatility, and lymph nodes.
High-yield: Fluctuation positive + transillumination positive = clear fluid (cystic hygroma, vaginal hydrocele, ranula). Fluctuation positive + transillumination negative = opaque/cellular content (sebaceous cyst, lipoma, cold abscess, dermoid).
Paget's test confirms fluctuation: pressure on one pole displaces fluid to make the opposite pole bulge, tested in two perpendicular planes. Brilliant transillumination = water-clear contents; Tyndall effect / no transillumination = thick, fatty, or solid contents.
Classification of skin & subcutaneous swellings
| Category | Examples | Key feature |
|---|---|---|
| Epithelial cysts | Epidermoid (sebaceous), pilar (trichilemmal) | Punctum, intradermal |
| Developmental cysts | Dermoid (sequestration, teratomatous), thyroglossal, branchial | Along lines of fusion |
| Acquired/implantation | Implantation dermoid | Site of trauma in fingers/palm |
| Fatty tumours | Lipoma, liposarcoma | Slip sign, lobulation |
| Synovial | Ganglion, bursae | Near joints/tendon sheaths |
| Neural | Neurofibroma, schwannoma | Mobile transverse, not vertical |
| Vascular | Haemangioma, AV malformation | Compressible, may pulsate |
Sebaceous cyst (epidermoid & pilar cyst)
A misnomer — most are epidermoid cysts arising from a blocked pilosebaceous follicle, lined by squamous epithelium and filled with keratin (not sebum). Pilar (trichilemmal) cysts arise from hair-follicle outer sheath and cluster on the scalp (often multiple, autosomal dominant).
Clinical features: smooth, spherical, intradermal swelling — skin cannot be moved over it (the cyst moves with skin). A punctum (blocked duct opening) is the signature, present in ~50%. Contents are toothpaste-like keratin with a rancid smell.
High-yield: The single best sign distinguishing a sebaceous cyst from a lipoma is fixity to skin (sebaceous = intradermal, skin not free; lipoma = subcutaneous, skin freely mobile over it).
Common sites: scalp, face, neck, scrotum, back. Never on palms and soles — these areas lack sebaceous glands/hair follicles (a favourite MCQ).
Complications (mnemonic — "I'm CALM"):
- Infection / abscess
- Cock's peculiar tumour — an infected, ulcerated, granulating sebaceous cyst that mimics a squamous cell carcinoma or epithelioma (classically scalp)
- Atheroma / sebaceous horn (hard projecting keratin)
- Large / calcification
- Malignant change (very rare)
Treatment: complete excision of the cyst with its wall; leaving wall remnants causes recurrence. Infected cysts → incision & drainage first, then delayed excision when quiet.
Dermoid cysts
Lined by squamous epithelium with skin appendages (hair, sebaceous & sweat glands) in the wall. Four types:
| Type | Mechanism | Classic site |
|---|---|---|
| Sequestration dermoid | Skin dermis sequestered along embryonic fusion lines | External angular dermoid (outer angle of eyebrow), root of nose, midline neck |
| Implantation dermoid | Traumatic forcing of epidermis into dermis | Fingers, palm (tailors, gardeners) |
| Tubulodermoid | Remnant of an unobliterated ectodermal tube | Thyroglossal cyst, post-anal dermoid |
| Teratomatous dermoid | Totipotent cells | Ovary, testis, retroperitoneum |
High-yield: External angular dermoid is the commonest sequestration dermoid — sits at the outer angle of the orbit, may extend intracranially, so CT/MRI before excision to rule out intracranial extension. A midline swelling could be an encephalocoele; never incise blindly.
Implantation dermoid appears at trauma-prone sites, is firm, and contains keratin. Sequestration dermoids are present from birth and may be fixed to bone (indentation/depression of underlying bone on X-ray).
Lipoma — "the universal tumour"
Benign tumour of mature adipocytes; arises anywhere fat exists ("universal tumour"), classically subcutaneous over the back, shoulders, and neck. Not found in the brain (no fat) — except for very rare locations.
Signs (the must-know triad):
- Slip sign — edge slips away from the examining finger (pathognomonic).
- Lobulation — surface feels lobulated due to fibrous septa.
- Skin freely mobile; soft, fluctuant (pseudofluctuation), and may transilluminate faintly.
High-yield: Lipoma can show pseudofluctuation and pseudotransillumination because fat is soft — do not confuse with a true cystic swelling. The slip sign is the clincher.
Syndromes/variants:
- Dercum's disease (adiposis dolorosa) — multiple painful lipomas, post-menopausal obese women.
- Madelung's disease (benign symmetrical lipomatosis) — neck "horse-collar" fat, alcoholic men.
- Multiple familial lipomatosis — autosomal dominant, numerous lipomas.
Concerning features for liposarcoma: size >5 cm, rapid growth, pain, fixity, deep/retroperitoneal location, recurrence. MRI is the investigation of choice for large/deep lesions; excision biopsy confirms. Retroperitoneal liposarcoma is the commonest retroperitoneal sarcoma.
Treatment: excision (cosmetic or if symptomatic/atypical).
Ganglion
The commonest swelling of the hand and wrist. A cystic, myxoid degeneration of joint capsule or tendon sheath, filled with clear gelatinous fluid. Not a true synovial cyst.
Sites: dorsum of wrist (commonest — over scapholunate ligament), flexor aspect of wrist, dorsum of foot, flexor tendon sheath of fingers ("seed/pearl ganglion").
Signs: smooth, tense, brilliantly transilluminant, more prominent on flexion of the wrist (becomes tense), well-defined, mobile but fixed to the deep structure.
High-yield: A ganglion is mobile side-to-side but fixed in the long axis of the tendon and becomes more prominent / tense on contracting the underlying tendon or flexing the joint.
Treatment: Many resolve spontaneously. Options: Reassurance/observation → aspiration ± steroid (high recurrence) → complete surgical excision (treatment of choice, lowest recurrence).
The old "hitting with the family Bible" method is abandoned (high recurrence, tissue trauma). Recurrence is common because of the deep stalk; meticulous excision of the root is key.
Neurofibroma & nerve sheath tumours
Arise from nerve sheath (Schwann + perineural fibroblasts). Solitary or part of neurofibromatosis (NF).
Signs: firm, fusiform swelling mobile transversely (side-to-side) but NOT in the line of the nerve (vertical fixity). Pressure may cause tingling/paraesthesia in the nerve's distribution.
| Feature | NF-1 (von Recklinghausen) | NF-2 |
|---|---|---|
| Gene/chromosome | NF1, chromosome 17 (neurofibromin) | NF2, chromosome 22 (merlin/schwannomin) |
| Hallmark | Multiple neurofibromas, café-au-lait (≥6, >15 mm), axillary freckling (Crowe sign) | Bilateral acoustic schwannomas (vestibular) |
| Eye | Lisch nodules (iris hamartomas) | Cataract |
| Bone | Sphenoid dysplasia, scoliosis | — |
| Malignant risk | MPNST (~5–10%) | Meningioma, ependymoma |
High-yield: NF-1 = chromosome 17, café-au-lait + Lisch nodules; NF-2 = chromosome 22, bilateral vestibular (acoustic) schwannomas. A neurofibroma that becomes painful, grows rapidly, or enlarges suggests malignant peripheral nerve sheath tumour (MPNST).
Schwannoma (neurilemmoma) arises only from Schwann cells, is encapsulated, eccentric to the nerve (can be shelled out preserving the nerve), with Antoni A (cellular, Verocay bodies) and Antoni B (loose) areas histologically.
Differential diagnosis of neck swellings (very high-yield)
Localise by triangle and movement.
Midline neck swellings:
| Swelling | Discriminating feature |
|---|---|
| Thyroglossal cyst | Moves up with swallowing AND tongue protrusion |
| Submental lymph node / dermoid | Doesn't move with tongue |
| Thyroid isthmus mass | Moves with swallowing only |
| Subhyoid bursa, ludwig's | Context-dependent |
Lateral neck swellings:
| Swelling | Discriminating feature |
|---|---|
| Branchial cyst | Upper third, anterior border of sternocleidomastoid, contains cholesterol crystals |
| Cystic hygroma | Posterior triangle, infancy, brilliantly transilluminant, compressible |
| Cold abscess / TB node | Matted nodes, cross-fluctuation |
| Carotid body tumour (chemodectoma) | Pulsatile, mobile side-to-side not up-down, at carotid bifurcation, "Fontaine sign" |
| Sternomastoid tumour | Infant, torticollis |
High-yield: Thyroglossal cyst moves up on protrusion of the tongue (tethered to hyoid/foramen caecum via thyroglossal tract) — the single most asked neck-swelling sign. Treatment is Sistrunk operation (excision of cyst + tract + central part of hyoid bone).
High-yield: Branchial cyst = remnant of 2nd branchial cleft, lies at the junction of upper and middle thirds, deep to the anterior border of sternocleidomastoid; aspirate shows cholesterol crystals. A branchial fistula opens at the lower third (anterior border of SCM).
High-yield: Cystic hygroma (lymphangioma) is brilliantly transilluminant, partially compressible, classically posterior triangle in infants; associated with Turner syndrome. Treatment of choice now is sclerotherapy (OK-432/picibanil, bleomycin) rather than surgery.
A practical bedside approach to any lump
Step 1 → Is it a swelling of skin or subcutaneous tissue? (Pinch the skin: moves with lump = skin/intradermal; skin free = subcutaneous or deeper.) Step 2 → Fluctuation? Positive = fluid/fat. Step 3 → Transillumination? Positive = clear fluid. Step 4 → Relation to surroundings: punctum (sebaceous), slip sign (lipoma), prominent on flexion (ganglion), transverse-only mobility (neurofibroma). Step 5 → Examine regional lymph nodes and the rest of the body (multiplicity → NF, lipomatosis).
Mnemonic for cyst contents on aspiration:
- Keratin/cheesy → epidermoid (sebaceous)
- Cholesterol crystals → branchial cyst
- Clear gelatinous → ganglion
- Straw-coloured/lymph → cystic hygroma
Investigations & investigation of choice
- Clinical examination is usually sufficient for sebaceous cyst, lipoma, and ganglion.
- Ultrasound — first-line imaging to confirm cystic vs solid, depth, and vascularity for any soft-tissue lump.
- MRI — investigation of choice for large/deep lipomas, suspected liposarcoma, nerve sheath tumours, and to map extent.
- CT/MRI before excising an external angular or midline dermoid (intracranial extension).
- FNAC / excision biopsy — when malignancy suspected (rapidly growing, >5 cm, fixed, painful).
- Thyroglossal/branchial cyst — USG neck + thyroid status (a thyroglossal "cyst" may be the only functioning thyroid tissue — confirm a normal thyroid before excision).
Management principles (drug/procedure of choice)
| Lesion | Treatment of choice |
|---|---|
| Sebaceous cyst | Complete excision with cyst wall |
| Cock's peculiar tumour | Wide excision (rule out SCC) |
| Dermoid cyst | Excision; image first if midline/angular |
| Lipoma | Excision if symptomatic/atypical |
| Liposarcoma | Wide local excision ± radiotherapy |
| Ganglion | Surgical excision of cyst + stalk |
| Neurofibroma (solitary, symptomatic) | Excision |
| Thyroglossal cyst | Sistrunk operation |
| Branchial cyst/fistula | Complete excision of tract |
| Cystic hygroma | Sclerotherapy (OK-432) first-line |
Recently asked / exam angle
- Image of a scalp swelling with a punctum → sebaceous (epidermoid) cyst; commonest scalp swelling.
- "Slip sign positive, skin freely mobile" → lipoma (universal tumour).
- Painful multiple lipomas in an obese woman → Dercum's disease.
- Wrist swelling more prominent on flexion, transilluminant → ganglion; excision = best treatment.
- Bilateral acoustic neuromas → NF-2 (chromosome 22); café-au-lait + Lisch nodules → NF-1 (chromosome 17).
- Swelling moving with tongue protrusion → thyroglossal cyst → Sistrunk operation.
- Cyst at anterior border of SCM with cholesterol crystals → branchial cyst.
- Infant, posterior triangle, brilliantly transilluminant → cystic hygroma; OK-432 sclerotherapy.
- Sebaceous cyst NOT on palms/soles (no sebaceous glands) — frequently asked one-liner.
- Cock's peculiar tumour — infected sebaceous cyst mimicking epithelioma.
- Antoni A/B and Verocay bodies → schwannoma histology.
Rapid revision
- Sebaceous (epidermoid) cyst — intradermal, has a punctum, skin not free; never on palms/soles; treat by complete excision with wall.
- Cock's peculiar tumour = infected, granulating sebaceous cyst mimicking SCC, classically scalp.
- Lipoma = universal tumour; slip sign + lobulation + skin freely mobile; pseudofluctuation/pseudotransillumination.
- Liposarcoma red flags: >5 cm, rapid growth, pain, deep/retroperitoneal; MRI is investigation of choice.
- Dercum's = painful lipomas; Madelung's = neck horse-collar lipomatosis in alcoholics.
- Ganglion = commonest hand/wrist swelling, myxoid degeneration, brilliantly transilluminant, prominent on flexion; excision is best.
- External angular dermoid = commonest sequestration dermoid; image before excising (intracranial extension).
- Implantation dermoid = trauma sites (fingers/palm) in manual workers.
- Neurofibroma moves transversely, not along the nerve; NF-1 chr 17 (café-au-lait, Lisch); NF-2 chr 22 (bilateral vestibular schwannoma).
- Thyroglossal cyst moves with tongue protrusion → Sistrunk operation; confirm normal thyroid first.
- Branchial cyst = deep to anterior border of SCM (upper/middle third junction), cholesterol crystals on aspiration.
- Cystic hygroma = posterior triangle, brilliantly transilluminant, infancy, Turner association; sclerotherapy (OK-432) is first-line.