Possible causes of parietal head bump
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Quick answer
A bump over the parietal area of the skull can have several causes. Many are harmless, but a new, enlarging, painful, or post-injury lump should be assessed.
Possible causes include:
- Normal skull shape or normal parietal prominence: Some people naturally have asymmetry or a noticeable bony contour.
- Minor scalp injury / bruise (hematoma): A recent knock can cause soft-tissue swelling, tenderness, discoloration, or a firm resolving lump.
- Pilar (trichilemmal) cyst or epidermoid cyst: Common benign scalp lumps. Usually smooth, round, mobile under the skin, and not painful unless inflamed.
- Lipoma: A soft, mobile, usually painless fatty lump under the scalp.
- Osteoma or other benign bony growth: A hard, fixed, slowly growing bump arising from the skull bone.
- Enlarged blood vessel or vascular lesion: Less common, sometimes compressible or pulsatile.
- Infection or abscess: More likely if it is red, warm, increasingly tender, draining, or accompanied by fever.
- Less common bone or scalp tumors: Considered particularly if the lump is rapidly growing, hard and fixed, unexplained, or associated with other symptoms.
Seek urgent medical care if it appeared after a significant head injury, is worsening, or comes with vomiting, severe or worsening headache, confusion, fainting, seizure, weakness/numbness, vision changes, fluid or blood from the nose/ears, or use of blood-thinning medication.
Arrange a routine clinician review if the bump is new and persists beyond 2 to 4 weeks, grows, becomes painful, feels hard/fixed, or you are unsure whether it is in the skin versus the bone. A physical examination, and occasionally ultrasound or CT, can clarify the cause.
Without trauma
Without trauma, a bump over the parietal skull can be due to:
- Normal skull contour or asymmetry: Parietal eminences are natural rounded prominences, often slightly unequal.
- Pilar (trichilemmal) cyst: A common firm, smooth, mobile scalp lump arising from a hair follicle. Usually painless.
- Epidermoid cyst: A slow-growing skin or scalp lump, sometimes with a small central pore.
- Lipoma: Soft, rubbery, mobile fatty lump under the scalp.
- Osteoma or other benign bony growth: Hard, fixed to the skull, usually very slow-growing and painless.
- Less commonly, an inflammatory/infectious lump, a congenital lesion, or a skull lesion that needs imaging to identify.
A hard, immobile bump that seems part of the bone should be examined by a clinician, particularly if it is new or enlarging. They may decide on an X-ray, ultrasound for a superficial scalp lump, or CT if a bony lesion is suspected.
Seek prompt medical assessment if it is rapidly growing, painful/tender, red or warm, draining, associated with fever, headaches, vomiting, seizures, weakness/numbness, vision changes, or if there is a history of cancer.
Differential diagnosis
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Finding Sources
Searching PubMed
scalp mass differential diagnosis
Searching the Web
scalp mass differential diagnosis osteoma pilar cyst clinical review
For a non-traumatic parietal scalp/head bump, the differential can be organized by whether it is in the skin/scalp or is actually part of the skull.
| Likely location/type | Differential diagnosis | Typical clues |
|---|---|---|
| Normal bone contour | Normal parietal eminence or skull asymmetry | Long-standing, hard, fixed, painless, unchanged |
| Hair-bearing scalp | Pilar (trichilemmal) cyst | Commonest scalp cyst; firm, smooth, mobile subcutaneous nodule, usually no central punctum. Most trichilemmal cysts occur on the scalp. |
| Epidermoid cyst | Mobile superficial lump, may have a central punctum; can become inflamed, tender, or discharge keratin | |
| Pilomatricoma | Hard or calcified skin nodule, often more common in children and young adults | |
| Dermoid cyst | Congenital, slow-growing, painless subcutaneous mass, often noticed in childhood | |
| Lipoma | Soft, lobulated, very mobile, painless | |
| Inflamed cyst / folliculitis / abscess | Tender, red, warm, sometimes draining, possibly fever | |
| Skull bone | Osteoma | Very hard, immobile, slow-growing, painless bony prominence |
| Fibrous dysplasia or other benign calvarial lesion | Fixed bony expansion or asymmetry; imaging distinguishes it | |
| Intraosseous hemangioma | Slowly enlarging bony skull mass, occasionally tender | |
| Paget disease of bone | Usually older adults; may have skull enlargement plus hearing or bone symptoms | |
| Less common but important | Proliferating trichilemmal tumor | Enlarging scalp mass, often arising from a longstanding pilar cyst |
| Primary skin cancer, soft-tissue sarcoma, lymphoma | Firm/fixed, ulcerated, bleeding, recurrent, or rapidly enlarging lesion | |
| Skull metastasis, multiple myeloma, other bone malignancy | New persistent bony mass, pain, rapid growth, systemic symptoms, or known cancer history |
Most likely possibilities, if it is a single painless lump without trauma, are:
- Normal parietal asymmetry
- Pilar cyst
- Epidermoid cyst
- Lipoma
- Osteoma, if it feels continuous with bone
A pilar cyst is characteristically a firm, mobile scalp nodule and is usually benign, as summarized by DermNet's pilar-cyst reference. The medical text search also notes that epidermal cysts are round, superficial, and freely mobile, while superficial masses are commonly benign cysts or lipomas.
Clinical distinction
- Moves with the scalp/skin: cyst, lipoma, skin lesion more likely.
- Rock-hard and cannot be moved at all: bony lesion or normal skull contour more likely.
- Soft and compressible: lipoma or vascular lesion.
- Red, warm, tender, or discharging: inflammation/infection.
- Rapidly enlarging, ulcerated, painful, or fixed: needs prompt in-person assessment.
A clinician can often diagnose this by palpation. Ultrasound is useful for a superficial scalp lump, while CT of the skull is generally more informative if it is hard and apparently arising from bone.
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