Granuloma is an inflammation found in many diseases. It is a collection of immune cells known as histiocytes (macrophages). Granulomas form when the immune system attempts to wall off substances it perceives as foreign but is unable to eliminate. Such substances include infectious organisms including bacteria and fungi, as well as other materials such as keratin and suture fragments.

The basis of management is to find and correct the underlying cause. Many times cats with EGC will respond to treatment with corticosteroids or to ciclosporin.

The exact cause of Majocchi's granuloma is not well established however a dysfunctinoal immune system may be a causative factor. The first form of MG, the superficial perifollicular form occurs predominately on the legs of otherwise healthy young women who repeatedly shave their legs and develop hair follicle occlusions that directly or indirectly disrupt the follicle and allow for passive introduction of the organism into the dermis. Hence, the physical barrier of the skin is important because it prevents the penetration of microorganisms. Physical factors that play a major role in inhibiting dermal invasion include the interaction among keratin production, the rate of epidermal turnover, the degree of hydration and lipid composition of the stratum corneum, CO levels, and the presence or absence of hair. Keratin and/or necrotic material can also be introduced into the dermis with an infectious organism to further enhance the problem. In immunocompromised individuals, the use of topical corticosteroids may lead to a dermatophyte infection due to local immunosuppression.

In , a granuloma is an organized collection of macrophages.

In medical practice, doctors occasionally use the term "granuloma" loosely to mean "a small nodule". Since a small nodule can represent anything from a harmless nevus to a malignant tumor, this usage of the term is not very specific. Examples of the inaccurate use of the term granuloma are the lesions known as vocal cord granuloma (known as contact granuloma), pyogenic granuloma and intubation granuloma, all of which are examples of granulation tissue, not granulomas. "Pulmonary hyalinizing granuloma" is a lesion characterized by keloid-like fibrosis in the lung, and is not granulomatous. Similarly, radiologists often use the term granuloma when they see a calcified nodule on X-ray or CT scan of the chest. They make this assumption since granulomas usually contain calcium, although the cells that form a granuloma are too tiny to be seen by a radiologist. The most accurate use of the term "granuloma" requires a pathologist to examine surgically removed and specially colored (stained) tissue under a microscope.

Macrophages (specifically histiocytes) are the cells that define a granuloma. They often, but not invariably, fuse to form multinucleated giant cells (Langhans giant cell). The macrophages in granulomas are often referred to as "epithelioid". This term refers to the vague resemblance of these macrophages to epithelial cells. Epithelioid macrophages differ from ordinary macrophages in that they have elongated nuclei that often resemble the sole of a slipper or shoe. They also have larger nuclei than ordinary macrophages and their cytoplasm is typically more pink when stained with eosin. These changes are thought to be a consequence of "activation" of the macrophage by the offending antigen.

The other key term in the above definition is the word "organized" that refers to a tight, ball-like formation. The macrophages in these formations are typically so tightly clustered that the borders of individual cells are difficult to appreciate. Loosely dispersed macrophages are not considered to be granulomas.

All granulomas, regardless of cause, may contain additional cells and matrix. These include lymphocytes, neutrophils, eosinophils, multinucleated giant cells, fibroblasts and collagen (fibrosis). The additional cells are sometimes a clue to the cause of the granuloma. For example, granulomas with numerous eosinophils may be a clue to coccidioidomycosis or allergic bronchopulmonary fungal disease, and granulomas with numerous neutrophils suggest blastomycosis, granulomatosis with polyangiitis, aspiration pneumonia or cat-scratch disease.

In terms of the underlying cause, the difference between granulomas and other types of inflammation is that granulomas form in response to antigens that are resistant to "first-responder" inflammatory cells such as neutrophils and eosinophils. The antigen causing the formation of a granuloma is most often an infectious pathogen or a substance foreign to the body, but sometimes the offending antigen is unknown (as in sarcoidosis).

Granulomas are seen in a wide variety of diseases, both infectious and non-infectious. Infections that are characterized by granulomas include tuberculosis, leprosy, histoplasmosis, cryptococcosis, coccidioidomycosis, blastomycosis and cat scratch disease. Examples of non-infectious granulomatous diseases are sarcoidosis, Crohn's disease, berylliosis, granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis, pulmonary rheumatoid nodules and aspiration of food and other particulate material into the lung.

An important feature of granulomas is whether or not they contain necrosis. Necrosis refers to dead cells that, under the microscope, appear as a mass of formless debris with no nuclei present. A related term, "caseation" (literally: turning to cheese) refers to a form of necrosis that, to the unaided eye (i.e., without a microscope), appears cheese-like ("caseous"), and is typically (but not uniquely) a feature of the granulomas of tuberculosis. The identification of necrosis in granulomas is important because granulomas with necrosis tend to have infectious causes. There are several exceptions to this general rule, but it nevertheless remains useful in day-to-day diagnostic pathology.

Annular elastolytic giant-cell granuloma (also known as "Giant cell elastophagocytosis," "Meischer's granuloma," "Miescher's granuloma of the face") is a cutaneous condition characterized histologically by a dermal infiltrate of macrophages.

Incision drainage with proper evacuation of the fluid followed by anti-tubercular medication.

The treatment of Majocchi's disease can be difficult because the condition can slowly progress and is chronic in nature. After a period of time, the lesions can reoccur. Even though the condition has improved, there is always the possibility of reoccurrence. There are treatments available to help improve the symptoms, however, there is no absolute cure for the disease. Some of these treatments include the application of topical steroids and lotions and ultraviolet therapy. The use of narrowband UVB and psoralen plus UVA have shown to be effective treatments for some patients with pigmented purpuric dermatoses. Majocchi granuloma also commonly occurs as a result of the use of potent topical steroids on unsuspected tinea. Historically, antifungal therapy has been successful in controlling MG in most instances. Therapies that have been used, included oral potassium iodide, mildly filtered local X-radiation, and topical applications of Asterol as a fungicide in both tincture and ointment forms. In modern medicine, systemic antifungals, such as griseofulvin, ketoconazole, and itraconazole, are the pillars of therapy, as they are safe and effective. The duration of therapy should be at least 4–8 weeks, and treatment should be continued until all lesions are cleared. Currently, no data about relapse rates or the complications of not treating Majocchi granuloma exist.

Eosinophilic granuloma is a form of Langerhans cell histiocytosis. It is a condition of both human and veterinary pathology. Colloquially, the reaction pattern is sometimes referred to as a rodent ulcer.

Feline eosinophilic granuloma complex is synonymous with "feline eosinophilic skin diseases". This is considered to be a cutaneous reaction pattern that can be the manifestation of a number of underlying infections, allergies or ectoparasite infestations. It can also be idiopathic, that is have no known underlying trigger. The eosinophilic reaction is common in feline inflammatory disease and the eosinophilic granuloma can be a hereditary reaction pattern in some lines of domestic cats.

The formation of gummata is rare in developed countries, but common in areas that lack adequate medical treatment.

Syphilitic gummas are found in most but not all cases of tertiary syphilis, and can occur either singly or in groups. Gummatous lesions are usually associated with long-term syphilitic infection; however, such lesions can also be a symptom of benign late syphilis.

Because granuloma annulare is usually asymptomatic and self-limiting with a course of about 2 years, initial treatment is generally topical steroid creams, followed by oral steroids and finally intradermal injections at the site of each ring. Treatment success varies widely, with most patients finding only brief success with the above-mentioned treatments. New research out of India suggests that the combination of rifampin (600 mg), ofloxacin (400 mg), and minocycline hydrochloride (100 mg) once monthly, or ROM therapy, produces promising results. Most lesions of granuloma annulare disappear in pre-pubertal patients with no treatment within two years while older patients (50+) have rings for upwards of 20 years. The appearance of new rings years later is not uncommon.

A dermatologist or general physician usually administers combination therapy of drugs used for tuberculosis, such as Rifampicin, Isoniazid and Pyrazinamide (possibly with either streptomycin or ethambutol).

Localized granuloma annulare has a tendency towards spontaneous resolution. Localized lesions have been treated with potent topical corticosteroids.

Treatment usually involves surgical removal of the lesion down to the bone. If there are any adjacent teeth, they are cleaned thoroughly with scaling and root planing (SRP) to remove any possible source of irritation. Recurrence is around 10%.

Supperative granuloma are chronic inflammatory cells at periphery with central abscess formation composed of histiocytes and multinucleated giant cells with central collections of neutrophils.

Prognosis is usually good, however recurrence may happen with rate up to 16%. Presence of myxoid structures in the pyogenic granuloma may be the main cause of recurrence.

Although pyogenic granulomas are not infectious or malignant, treatment may be considered because of bleeding or ulceration. Frequently, pyogenic granulomas are treated with electrodesiccation (cauterization) and curettage (excision), though laser treatment using pulsed dye laser or CO laser is often effective.

Several reports have demonstrated the efficacy of topical application of the beta-adrenergic antagonist timolol in the treatment of pediatric pyogenic granuloma.

There is usually no treatment if the pyogenic granuloma occurs during pregnancy since the lesion may heal spontaneously. Recurrent bleeding in either oral or nasal lesions may necessitate excision and cauterization sooner, however. If aesthetics are a concern, then treatment may be pursued as well. Usually, only minor surgery may be needed, along with a dental cleaning for oral lesions to remove any calculus or other source of irritation. For nasal lesions, nose-picking should be discouraged.

In longstanding scarred lesions, squamous cell carcinoma can develop.

Tuberculous lymphadenitis (or tuberculous adenitis) is a chronic specific granulomatous inflammation of the lymph node with caseation necrosis, caused by infection with "Mycobacterium tuberculosis" or "Mycobacterium bovis".

The characteristic morphological element is the tuberculous granuloma (caseating tubercule). This consists of giant multinucleated cells and (Langhans cells), surrounded by epithelioid cells aggregates, T cell lymphocytes and fibroblasts. Granulomatous tubercules eventually develop central caseous necrosis and tend to become confluent, replacing the lymphoid tissue.

In syphilis, the gumma is caused by reaction to spirochaete bacteria in the tissue.

It appears to be the human body's way to slow down the action of this bacteria, it is a unique immune response that develops in humans after the immune system fails to kill off syphilis.

Actinic granuloma (also known as "O'Brien granuloma") is a cutaneous condition characterized histologically by a dermal infiltrate of macrophages.

Actinic granuloma is an asymptomatic granulomatous reaction that affects sun-exposed skin, most commonly on the face, neck, and scalp.

It is characterized by annular or polycyclic lesions that slowly expand centrifugally and have an erythematous elevated edge and a hypopigmented, atrophic center.

Advise to reduce exposure to the sun and to use sunscreen.

Treatment with topical halometasone cream, pimecrolimus cream.

A fibrin ring granuloma, also known as doughnut granuloma, is a histopathological finding that is characteristic of Q fever. On hematoxylin-eosin staining, the fibrin ring granuloma consists of a central lipid vacuole (usually washed-out during fixing and staining, leaving only an empty hole) surrounded by a dense red fibrin ring and epithelioid macrophages. Fibrin ring granulomas may also be seen in Hodgkin's disease and infectious mononucleosis.

Pulmonary hyalinizing granuloma is a lesional pattern of pulmonary inflammatory pseudotumor.

Patch-type granuloma annulare (also known as "Macular granuloma annulare") is a skin condition of unknown cause, more commonly affecting women between 30 and 70 years of age, characterized by flat or slightly palpable erythematous or red-brown skin lesions.

The foreign body granuloma is a response of biological tissue to any foreign material in the tissue. Tissue-encapsulation of an implant is part of this. An infection around a splinter is part of this, too.

The presence of the implant changes the healing response, and this is called the foreign-body reaction (FBR). FBR consists of: protein adsorption, macrophages, multinucleated foreign body giant cells (macrophage fusion), fibroblasts, and angiogenesis.

It can be caused by beryllium.

Pulmonary hyalinizing granuloma is characterized by localized changes in lung architecture determinated by deposition of hyaline collagenous fibrosis accompanied by sparse lymphocytic infiltrate that compresses and distorts the remaining bronchioles. A higher magnification, the mass is composed by hypocellular collagen lamellae.

The disease is effectively treated with antibiotics, therefore, developed countries have a very low incidence of donovanosis; about 100 cases reported each year in the United States. However, sexual contacts with individuals in endemic regions dramatically increases the risk of contracting the disease. Avoidance of these sexual contacts, and sexually transmitted disease testing before beginning a sexual relationship, are effective preventative measures for donovanosis.