Finding a lump or bump on the back of your head, particularly near the base of the skull, can cause concern. Most of these masses are benign, relating to normal anatomy, minor skin conditions, or temporary reactions to injury or infection. This article provides an overview of the most common explanations for a bump in this region. Remember that this information is for educational purposes only, and any persistent, painful, or concerning bump requires diagnosis from a medical professional.
Is It Just Normal Anatomy?
The most frequent reason for feeling a hard lump on the back of the skull is the presence of a normal bony structure. The External Occipital Protuberance (EOP) is a noticeable bony prominence where the neck muscles attach to the skull. This structure, part of the occipital bone, can feel like a hard knot when touched.
The size of the EOP varies considerably among individuals, often being more pronounced in males. When exaggerated, it is sometimes referred to as an occipital spur, which may be easily felt and potentially tender. Because it is a fixed part of the skull, this bump is completely immovable. Normal variations in the prominence of the cervical vertebrae, such as the C7 spinous process, can also be mistaken for a lump lower down in the neck.
Common Benign Growths of the Skin and Scalp
Many lumps are harmless growths arising from the skin or underlying soft tissue. The most common are cysts and fatty tumors, which develop slowly over time. These growths are differentiated from bone by their mobility when pressed.
Epidermoid Cysts
Epidermoid cysts are common slow-growing masses. They form when surface skin cells become trapped beneath the skin, creating a sac filled with keratin, a thick, cheesy substance. These cysts are usually flesh-colored or yellowish, firm, and movable over the deeper tissue. They can range from pea-sized to several centimeters, and sometimes a small dark spot (punctum) is visible, representing the opening of a blocked hair follicle.
Lipomas and Trichilemmal Cysts
Another frequent finding is the lipoma, a non-cancerous tumor composed of fat tissue. Lipomas feel soft and rubbery, and they are easily movable beneath the skin. These growths tend to be painless and grow very slowly, often reaching 2 to 10 centimeters. Less common are trichilemmal cysts, often found on the scalp, which are firm, mobile nodules that typically lack the central punctum seen in epidermoid cysts.
Bumps Related to Infection or Injury
A bump that appears quickly, is painful, or feels warm often indicates injury or infection. The most common reactive masses in the occipital region are swollen lymph nodes. These small, oval-shaped glands are part of the immune system, filtering fluid from the scalp and neck.
When a local infection occurs, such as scalp irritation or ringworm, these lymph nodes become enlarged and tender as they fight the invading organisms. These swollen nodes, called lymphadenopathy, are usually movable and soft or rubbery. The swelling typically subsides once the underlying infection resolves, but persistent swelling lasting more than a few weeks warrants further investigation.
Bumps arising from direct trauma often present as a hematoma, commonly known as a “goose egg.” This is a localized collection of clotted blood underneath the skin that forms rapidly after a blow to the head. Hematomas are initially soft and tender, often accompanied by bruising, but they resolve naturally as the body reabsorbs the blood. An abscess or boil is another inflammatory bump, characterized by a collection of pus that is red, warm, and acutely painful, forming when a hair follicle or skin gland becomes deeply infected.
When to Seek Medical Evaluation
While most lumps are benign, certain characteristics should prompt a medical evaluation to rule out serious conditions. A physical examination by a healthcare provider, assessing the lump’s texture, mobility, and tenderness, is the first step in diagnosis. Depending on the findings, a doctor might recommend imaging studies like an ultrasound or a biopsy for tissue analysis.
You should seek prompt medical attention if you notice any of the following symptoms:
- Rapid growth: Any lump that increases significantly in size over a short period.
- Fixation and hardness: A bump that feels immobile or fixed to the underlying bone or deep tissue.
- Accompanying systemic symptoms: Unexplained fever, night sweats, or unintentional weight loss.
- Persistent pain: Severe or worsening pain not related to a recent injury.
- Skin changes: The bump bleeds, ulcerates, or shows changes in color or texture.