Fever, headache, and neurological problems, while classic, only occur in 20% of people with brain abscess.

The famous triad of fever, headache and focal neurologic findings are highly suggestive of brain abscess. These symptoms are caused by a combination of increased intracranial pressure due to a space-occupying lesion (headache, vomiting, confusion, coma), infection (fever, fatigue etc.) and focal neurologic brain tissue damage (hemiparesis, aphasia etc.).

The most frequent presenting symptoms are headache, drowsiness, confusion, seizures, hemiparesis or speech difficulties together with fever with a rapidly progressive course. Headache is characteristically worse at night and in the morning, as the intracranial pressure naturally increases when in the supine position. This elevation similarly stimulates the medullary vomiting center and area postrema, leading to morning vomiting.

Other symptoms and findings depend largely on the specific location of the abscess in the brain. An abscess in the cerebellum, for instance, may cause additional complaints as a result of brain stem compression and hydrocephalus. Neurological examination may reveal a stiff neck in occasional cases (erroneously suggesting meningitis).

Abscesses may occur in any kind of solid tissue but most frequently on skin surface (where they may be superficial pustules (boils) or deep skin abscesses), in the lungs, brain, teeth, kidneys, and tonsils. Major complications are spreading of the abscess material to adjacent or remote tissues, and extensive regional tissue death (gangrene).

The main symptoms and signs of a skin abscess are redness, heat, swelling, pain, and loss of function. There may also be high temperature (fever) and chills.

An internal abscess is more difficult to identify, but signs include pain in the affected area, a high temperature, and generally feeling unwell.

Internal abscesses rarely heal themselves, so prompt medical attention is indicated if such an abscess is suspected.

An abscess could potentially be fatal (although this is rare) if it compresses vital structures such as the trachea in the context of a deep neck abscess.

If superficial, abscesses may be fluctuant when palpated. This is a wave-like motion that is caused by movement of the pus inside the abscess.

Surgery of the anal fistula to drain an abscess treats the fistula and reduces likelihood of its recurrence and the need for repeated surgery. There is no evidence that fecal incontinence is a consequence of this surgery for abscess drainage.

Perianal abscesses can be seen in patients with for example inflammatory bowel disease (such as Crohn's disease) or diabetes. Often the abscess will start as an internal wound caused by ulceration, hard stool or penetrative objects with insufficient lubrication. This wound typically becomes infected as a result of the normal presence of feces in the rectal area, and then develops into an abscess. This often presents itself as a lump of tissue near the anus which grows larger and more painful with time. Like other abscesses, perianal abscesses may require prompt medical treatment, such as an incision and debridement or lancing.

Brain abscess (or cerebral abscess) is an abscess caused by inflammation and collection of infected material, coming from local (ear infection, dental abscess, infection of paranasal sinuses, infection of the mastoid air cells of the temporal bone, epidural abscess) or remote (lung, heart, kidney etc.) infectious sources, within the brain tissue. The infection may also be introduced through a skull fracture following a head trauma or surgical procedures. Brain abscess is usually associated with congenital heart disease in young children. It may occur at any age but is most frequent in the third decade of life.

Localized pain, often nocturnal, alleviated by aspirin. Often mimics the symptoms of Osteoid osteoma, which is typically less than 1 cm in diameter.

An epidural abscess refers to a collection of pus and infectious material located in the epidural space of the central nervous system. Due to its location adjacent to brain or spinal cord, epidural abscesses have the potential to cause weakness, pain, and paralysis.

Fever, sore throat, odynophagia (painful swallowing), swelling in neck.

Spinal epidural abscess (SEA) is a collection of pus or inflammatory granulation between the dura mater and the vertebral column. Currently the annual incidence rate of SEAs is estimated to be 2.5-3 per 10,000 hospital admissions. Incidence of SEA is on the rise, due to factors such as an aging population, increase in use of invasive spinal instrumentation, growing number of patients with risk factors such as diabetes and intravenous drug use. SEAs are more common in posterior than anterior areas, and the most common location is the thoracolumbar area, where epidural space is larger and contains more fat tissue.

SEAs are more common in males, and can occur in all ages, although highest prevalence is during the fifth and seventh decades of life.

Pott's puffy tumor, first described by Sir Percivall Pott in 1760, is a rare clinical entity characterized by subperiosteal abscess associated with osteomyelitis. It is characterized by an osteomyelitis of the frontal bone, either direct or through haematogenic spread. This results in a swelling on the forehead, hence the name. The infection can also spread inwards, leading to an intracranial abscess. Pott's puffy tumor can be associated with cortical vein thrombosis, epidural abscess, subdural empyema, and brain abscess. The cause of vein thrombosis is explained by venous drainage of the frontal sinus, which occurs through diploic veins, which communicate with the dural venous plexus; septic thrombi can potentially evolve from foci within the frontal sinus and propagate through this venous system. This type of chronic osteomyelitis of the frontal bone is confused with acute sub-periosteal abscess of the frontal bone, which presents as a discrete collection over the frontal sinus.

Although it can affect all ages, it is mostly found among teenagers and adolescents. It is usually seen as a complication of frontal sinusitis or trauma. Medical imaging can be of use in the diagnosis and evaluation of the underlying cause and extent of the condition. Ultrasound is able to identify frontal bone osteomyelitis, while computed tomography (CT) can evaluate bony erosion, and along with magnetic resonance imaging (MRI), can better appreciate the underlying cause and extent of possible intra-cranial extension/involvement.

Anterior space abscess can cause trismus (spasm of jaw muscle) and hard mass formation along the angle of the mandible, with medial bulging of the tonsil and lateral pharyngeal wall. Posterior space abscess causes swelling in posterior pharyngeal wall. Trismus (spasm of jaw muscle) is minimal. Posterior abscess may involve structures within the carotid sheath, causing rigors, high fever, bacteremia, neurologic deficit, massive haemorrhage caused by carotid artery rupture.

A Brodie abscess is a subacute osteomyelitis, which may persist for years before converting to a frank osteomyelitis. Classically, this may present after conversion as a draining abscess extending from the tibia out through the shin. Occasionally acute osteomyelitis may be contained to a localized area and walled off by fibrous and granulation tissue. This is termed Brodie's abscess.

Most frequent causative organism is Staphylococcus aureus.

An unremoved infected abscess may lead to sepsis. Also, multiple abscesses may occur. Other complications may include fistula formation and recurrent pancreatitis.

A Paget's abscess, named by eminent British surgeon and pathologist Sir James Paget, is an abscess that recurs at the site of a former abscess which had resolved.

Unlike tonsillitis, which is more common in the children, PTA has a more even age spread, from children to adults. Symptoms start appearing two to eight days before the formation of an abscess. A progressively severe sore throat on one side and pain during swallowing (odynophagia) usually are the earliest symptoms. As the abscess develops, persistent pain in the peritonsillar area, fever, a general sense of feeling unwell, headache and a distortion of vowels informally known as "hot potato voice" may appear. Neck pain associated with tender, swollen lymph nodes, referred ear pain and foul breath are also common. While these signs may be present in tonsillitis itself, a PTA should be specifically considered if there is limited ability to open the mouth (trismus).

Physical signs of a peritonsillar abscess include redness and swelling in the tonsillar area of the affected side and swelling of the jugulodigastric lymph nodes. The uvula may be displaced towards the unaffected side.

An odontogenic infection is an infection that originates within a tooth or in the closely surrounding tissues. The term is derived from "" (from ancient Greek "odous" - "tooth") and "" (from Greek "genos" - "birth"). Odontogenic infections may remain localized to the region where they started, or spread into adjacent or distant areas.

It is estimated that 90-95% of all orofacial infections originate from the teeth or their supporting structures. Furthermore, about 70% of odontogenic infections occur as periapical inflammation, i.e. acute periapical periodontitis or a periapical abscess. The next most common form of odontogenic infection is the periodontal abscess.

Patients with pancreatic abscesses may experience abdominal pain, chills and fever or the inability to eat. Whereas some patients present an abdominal mass, others do not. Nausea and vomiting may also occur.

The pain is continuous and may be described as extreme, growing, sharp, shooting, or throbbing. Putting pressure or warmth on the tooth may induce extreme pain. The area may be sensitive to touch and possibly swollen as well. This swelling may be present at either the base of the tooth, the gum, and/or the cheek, and sometimes can be reduced by applying ice packs.

An acute abscess may be painless but still have a swelling present on the gum. It is important to get anything that presents like this checked by a dental professional as it may become chronic later.

In some cases, a tooth abscess may perforate bone and start draining into the surrounding tissues creating local facial swelling. In some cases, the lymph glands in the neck will become swollen and tender in response to the infection. It may even feel like a migraine as the pain can transfer from the infected area. The pain does not normally transfer across the face, only upwards or downwards as the nerves that serve each side of the face are separate.

Severe aching and discomfort on the side of the face where the tooth is infected is also fairly common, with the tooth itself becoming unbearable to touch due to extreme amounts of pain.

A subcutaneous abscess is an abscess located in the subcutaneous tissue (also hypodermis). The abscess is formed due to a hypodermal infection by a bacterium, a fungus or a parasite. Typically, this kind of abscess needs drainage, usually for a minimum of 24 hours, by means of gauze packing or a Penrose drain.

The signs and symptoms depend upon the type of OM, and may include:

- Pain, which is severe, throbbing and deep seated.

- Initially fistula are not present.

- No dental pain, but headache or other facial pain, as in the descriptive former term "neuralgia-inducing" (cavitational osteonecrosis).

- Fibromyalgia.

- Chronic fatigue syndrome.

- Swelling. External swelling is initially due to inflammatory edema with accompanying erythema (redness), heat and tenderness, and then later may be due to sub-periosteal pus accumulation. Eventually, subperiosteal bone formation may give a firm swelling.

- Trismus (difficulty opening the mouth), which may be present in some cases and is caused by edema in the muscles.

- Dysphagia (difficulty swallowing), which may be present in some cases and is caused by edema in the muscles.

- Cervical lymphadenitis (swelling of the lymph nodes in the neck).

- Aesthesia or paresthesia (altered sensation such as numbness or pins and needles) in the distribution of the mental nerve.

- Fever which may be present in the acute phase and is high and intermittent

- Malaise (general feeling of being unwell) which may be present in the acute phase

- Anorexia (loss of appetite).

- Leukocytosis (elevated numbers of white blood cells) which may be present in the acute phase

- Elevated erythrocyte sedimentation rate and C reactive protein are sometimes present.

- An obvious cause in the mouth (usually) such as a decayed tooth.

- Teeth that are tender to percussion, which may develop as the condition progresses

- Loosening of teeth, which may develop as the condition progresses.

- Pus may later be visible, which exudes from around the necks of teeth, from an open socket, or from other sites within the mouth or on the skin over the involved bone.

- Fetid odor.

Unlike acute OM in the long bones, acute OM in the jaws gives only a moderate systemic reaction and the person remains surprisingly well. Acute OM of the jaws may give a similar appearance to a typical odontogenic infection, but cellulitis does not tend to spread from the periosteal envelope of the involved bone. If the infection is not controlled, the process becomes chronic and systemic symptoms are usually present, including draining fistulas, loosening of teeth and sequestra formation. Untreated chronic osteomyelitis tends to feature occasional acute exacerbations.

This condition is often initially misdiagnosed as hemorrhoids, since this is almost always the cause of any sudden anal discomfort. The presence of the abscess, however, is suspected when the pain quickly worsens over one or two days and usual hemorrhoid treatments are ineffective in bringing relief. Furthermore, any serious abscess will eventually begin to cause signs and symptoms of general infection, including fever and nighttime chills.

A physician can rule out a hemorrhoid with a simple visual inspection, and usually appreciate an abscess by touch.

The main types of dental abscess are:

- Periapical abscess: The result of a chronic, localized infection located at the tip, or apex, of the root of a tooth.

- Periodontal abscess: begins in a periodontal pocket (see: periodontal abscess)

- Gingival abscess: involving only the gum tissue, without affecting either the tooth or the periodontal ligament (see: periodontal abscess)

- Pericoronal abscess: involving the soft tissues surrounding the crown of a tooth (see: Pericoronitis)

- Combined periodontic-endodontic abscess: a situation in which a periapical abscess and a periodontal abscess have combined (see: Combined periodontic-endodontic lesions).

Sinusitis is inflammation of the paranasal air sinuses. Infections associated with teeth may be responsible for approximately 20% of cases of maxillary sinusitis. The cause of this situation is usually a periapical or periodontal infection of a maxillary posterior tooth, where the inflammatory exudate has eroded through the bone superiorly to drain into the maxillary sinus. Once an odontogenic infection involves the maxillary sinus, it is possible that it may then spread to the orbit or to the ethmoid sinus.

Pain in the perianal area is the most common symptom of an anorectal abscess. The pain may be dull, aching, or throbbing. It is worst when the person sits down and right before a bowel movement. After the individual has a bowel movement, the pain usually lessens. Other signs and symptoms of anorectal abscess include constipation, drainage from the rectum, fever and chills, or a palpable mass near the anus.

The condition invariably becomes extremely painful, and usually worsens over the course of just a few days. The pain may be limited and sporadic at first, but invariably worsens to a constant pain which can become very severe when body position is changed (e.g., when standing up, rolling over, and so forth). Depending upon the exact location of the abscess, there can also be excruciating pain during bowel movements, though this is not always the case. This condition may occur in isolation, but is frequently indicative of another underlying disorder, such as Crohn's disease.

Signs and symptoms may include stiff neck (limited neck mobility or torticollis), some form of palpable neck pain (may be in "front of the neck" or around the Adam's Apple), malaise, difficulty swallowing, fever, stridor, drooling, croup-like cough or enlarged cervical lymph nodes. Any combination of these symptoms should arouse suspicion of RPA.

Peritonsillar abscess (PTA), also known as a quinsy, is pus due to an infection behind the tonsil. Symptoms include fever, throat pain, trouble opening the mouth, and a change to the voice. Pain is usually worse on one side. Complications may include blockage of the airway or aspiration pneumonitis.

They are typically due to infection by a number of types of bacteria. Often it follows streptococcal pharyngitis. They do not typically occur in those who have had a tonsillectomy. Diagnosis is usually based on the symptoms. Medical imaging may be done to rule out complications.

Treatment is by removing the pus, antibiotics, sufficient fluids, and pain medication. Steroids may also be useful. Admission to hospital is generally not needed. In the United States about 3 per 10,000 people per year are affected. Young adults are most commonly affected.