Thyroid abscess is a localized suppurative infection within the thyroid gland. It is an extremely rare condition because the thyroid gland has natural resistance to infection due to its rich blood supply, lymphatic drainage, capsular structure, and high iodine content. It most commonly develops in immunosuppressed patients (HIV, diabetes, chemotherapy), children with piriform sinus fistula, or in the setting of pre-existing thyroid pathology (nodular goiter, cyst). Urgent drainage and antibiotic therapy are required.
Age Range
20-60
Peak Age
35
Gender
Equal
Prevalence
Rare
Thyroid abscess typically develops via three routes: (1) Piriform sinus fistula — oropharyngeal flora reaches the thyroid gland through a congenital fistula extending from the piriform sinus to the thyroid gland as a remnant of the left 3rd or 4th branchial arch. Therefore, recurrent left thyroid abscess in children and young adults should suggest piriform sinus fistula. (2) Hematogenous or lymphatic spread — bacterial dissemination from a distant infectious focus, especially in immunosuppressed patients. (3) Direct extension — from adjacent deep neck infection or infected thyroid cyst. In abscess formation, bacteria initiate an acute inflammatory response in thyroid tissue — neutrophil infiltration, tissue necrosis, and pus formation occur. The pus collection from liquefaction necrosis appears as a central hypodense/hypoechoic area on imaging. The inflammatory response in surrounding thyroid tissue with edema and hyperemia is reflected as rim enhancement and surrounding soft tissue thickening. Internal debris and gas bubbles (in anaerobic bacteria) determine the imaging findings of abscess contents.
The most reliable imaging finding combination of thyroid abscess is a rim-enhancing collection on contrast-enhanced imaging with marked diffusion restriction of the same collection on DWI. Rim enhancement reflects vascularity of granulation tissue, while diffusion restriction reflects viscous pus content. The combination of these two findings provides reliable differentiation from necrotic tumor, simple cyst, and infected cyst.
Thick, irregularly walled, cystic/semi-cystic collection with heterogeneous internal echoes within or adjacent to the thyroid gland. Internal debris may move in a gravity-dependent manner (dynamic assessment). Surrounding thyroid parenchyma becomes diffusely hypoechoic and heterogeneous (inflammatory changes). The abscess wall is irregular, thick, and hypoechoic, clearly distinguishable from surrounding intact thyroid tissue. If gas bubbles are present, they appear as bright echogenic foci with reverberation artifact.
Report Sentence
A __ x __ mm thick and irregularly walled cystic collection with internal debris is seen in the [right/left] thyroid lobe. Diffuse inflammatory changes are present in surrounding thyroid parenchyma. Gas bubbles [are present/are not identified]. Findings are consistent with thyroid abscess.
On color Doppler, markedly increased vascularity (hyperemia) in the abscess wall and surrounding inflammatory thyroid tissue. No vascularity is seen in the abscess center (pus collection) — avascular central area. This peripheral hypervascularity + avascular center pattern supports abscess diagnosis. Diffusely increased vascularity may also be seen in surrounding intact thyroid tissue (reactive hyperemia).
Report Sentence
On Doppler examination, markedly increased vascularity is seen in the periphery of the collection and surrounding thyroid tissue. The center of the collection is avascular. Peripheral hypervascularity + avascular center pattern is consistent with abscess.
On contrast-enhanced CT, a rim (ring) enhancing hypodense collection within or adjacent to the thyroid gland. The abscess wall enhances prominently while the central pus collection does not enhance and remains hypodense (0-25 HU). Edema and increased enhancement in surrounding thyroid parenchyma, stranding in perithyroidal fat tissue are seen. Internal gas bubbles appear as small foci of air density (-1000 HU). In advanced cases, the abscess may extend beyond the thyroid into deep neck spaces.
Report Sentence
On contrast-enhanced CT, a __ x __ mm rim-enhancing hypodense collection is seen in the [right/left] thyroid lobe. Internal gas bubbles [are present/are not identified]. Inflammatory changes in surrounding thyroid parenchyma and stranding in perithyroidal fat tissue are seen. Findings are consistent with thyroid abscess.
A thin tract structure extending from the left piriform sinus to the thyroid gland may be seen on non-contrast or contrast-enhanced CT. This tract represents a congenital fistula as a remnant of the 3rd or 4th branchial arch. The fistula tract is usually located on the left side (>90%). During active infection, edema and thickening are seen along the fistula tract; during remission, the fistula is very thin and difficult to detect. The fistula opening can be confirmed by barium swallow or direct laryngoscopy.
Report Sentence
A thin tract structure extending from the left piriform sinus to the left thyroid lobe is seen on CT. This finding is consistent with piriform sinus fistula (3rd/4th branchial arch remnant) and explains the etiology of recurrent thyroid abscess.
The abscess collection shows hyperintense signal on T2-weighted sequences (fluid/pus content). The abscess wall appears as a thin to thick ring with low signal on T2. Periabscess edema (increased T2 signal) is seen in surrounding thyroid parenchyma and soft tissues. Internal debris may show heterogeneous signal on T2. MRI is superior to CT for multiplanar assessment of abscess extent and extension — especially for demonstrating piriform sinus fistula tract.
Report Sentence
A hyperintense collection is seen in the [right/left] thyroid lobe on T2-weighted sequences. Hypointense wall structure and periabscess edema are present around the collection. Piriform sinus fistula tract [is identified/is not identified].
The abscess collection shows markedly high signal on DWI and low signal on ADC map (true diffusion restriction). High protein, cellular debris, and viscous content in the pus collection create diffusion restriction. This finding is an important distinguishing feature from simple cyst or necrotic tumor (which do not show diffusion restriction).
Report Sentence
Marked diffusion restriction is seen in the thyroid collection on DWI (ADC: __ x 10⁻³ mm²/s). This finding, unlike simple cyst or necrotic lesion, is consistent with viscous pus collection and supports abscess diagnosis.
Criteria
Left thyroid localization, young age (<20), recurrent infection attacks, piriform sinus-thyroid fistula tract on CT/MRI. 3rd or 4th branchial arch remnant.
Distinct Features
Thin tract from left piriform sinus to left thyroid lobe on CT/MRI. Tract is edematous and thick during active infection. Fistula opening can be confirmed with barium swallow. Definitive treatment is thyroidectomy + fistula excision. Antibiotics alone are insufficient — recurrent infection is inevitable as long as the fistula exists.
Criteria
Thyroid abscess developing in the setting of immunosuppressive condition (HIV, uncontrolled diabetes, chemotherapy, organ transplantation). Opportunistic pathogens (fungi, mycobacteria) may be causative.
Distinct Features
May be bilateral or multifocal. Atypical imaging findings possible due to opportunistic pathogens. Fungal abscess may show granulomatous pattern. Mycobacterial abscess may be associated with caseous necrosis — may contain calcification. Treatment is control of underlying immunosuppressive condition + prolonged antimicrobial therapy.
Criteria
Secondary infection of pre-existing thyroid cyst or nodule. Usually develops after FNA or trauma. Underlying pathology (multinodular goiter, cyst) is recognizable.
Distinct Features
Pre-existing nodules or cysts are seen around the abscess on US/CT. Abscess boundaries may follow the structure of underlying pathology. FNA history is important anamnestic information. Treatment is drainage + antibiotics; underlying pathology should be evaluated for surgical indication.
Distinguishing Feature
Simple cyst is a thin-walled, anechoic, non-enhancing cystic lesion WITHOUT diffusion restriction on DWI. Abscess is thick-walled, contains internal debris, shows rim enhancement, and demonstrates diffusion restriction on DWI. Clinically, abscess presents with pain, fever, and leukocytosis while simple cyst is asymptomatic.
Distinguishing Feature
Subacute thyroiditis (De Quervain) shows diffuse or focal hypoechoic areas but does not form an organized pus collection — no fluid-debris level or rim enhancement. In subacute thyroiditis, vascularity is DECREASED on Doppler (hypothyroid phase), while surrounding hypervascularity is increased in abscess. In subacute thyroiditis, ESR is markedly elevated and radioactive iodine uptake is low.
Distinguishing Feature
Anaplastic carcinoma may contain necrotic areas and can be confused with abscess; however, in anaplastic carcinoma the solid enhancing component is DOMINANT and necrotic areas are centrally located. In abscess, there is no solid enhancing component — only rim enhancement is seen. In anaplastic carcinoma, diffusion restriction is seen in solid components on DWI, while in abscess, diffusion restriction is seen in the collection itself. Clinically, anaplastic carcinoma has a chronic course while abscess is acute.
Distinguishing Feature
Hemorrhagic cyst shows high signal on T1 (methemoglobin), abscess shows low-intermediate signal on T1. Rim enhancement is generally absent or very thin in hemorrhagic cyst, while prominent thick rim enhancement is seen in abscess. On DWI, hemorrhagic cyst generally does not show diffusion restriction, while abscess shows marked restriction. Hemorrhagic cyst is usually painless without fever.
Urgency
emergentManagement
interventionalBiopsy
Not NeededFollow-up
specialist-referralThyroid abscess is an infectious emergency requiring urgent treatment. The first step is broad-spectrum intravenous antibiotic therapy (empiric: amoxicillin-clavulanate or ampicillin-sulbactam + metronidazole). Small abscesses (<3 cm) can be drained by US-guided needle aspiration; large or complex abscesses require surgical drainage. In piriform sinus fistula-associated abscess, fistula excision + left lobectomy should be performed 6-8 weeks after acute infection is controlled — otherwise recurrence is inevitable. Fistula diagnosis should be confirmed by barium swallow or direct laryngoscopy. Culture and sensitivity testing should be performed from drainage material. Complications: deep neck abscess, mediastinitis, sepsis, airway obstruction, internal jugular vein thrombophlebitis. Control of underlying condition is essential in immunosuppressed patients.
Thyroid abscess is an infection requiring urgent treatment. Broad-spectrum antibiotics + percutaneous drainage or surgical drainage are treatment options. Piriform sinus fistula should be investigated in children. Fungal etiology should be considered in immunosuppressed patients. Complications: mediastinitis, sepsis, airway obstruction.