Cystic thyroid nodules

INTRODUCTION — Thyroid nodules are common, and a large proportion has mixed cystic and solid components. In some studies, a nodule is called a cyst only if it is predominantly cystic on ultrasonography, but in others, the term is applied to nodules that have any areas of cystic degeneration, which may include up to 50 percent of thyroid nodules. Most cysts recur after fine-needle aspiration (FNA).

This topic review will focus on the unique challenges presented by patients with cystic thyroid lesions. The general approach to thyroid nodules is reviewed separately. (See "Diagnostic approach to and treatment of thyroid nodules".) (Related Pathway(s): Thyroid nodules: Initial evaluation in adults and Thyroid nodules: Initial evaluation in pregnant patients.)

CLINICAL PRESENTATION — Like most thyroid nodules, cystic thyroid nodules often come to attention when noted by the patient or as an incidental finding during a routine physical examination or radiologic procedure such as carotid ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI) of the neck (so-called "thyroid incidentalomas") [1].

However, some patients develop symptoms, and cystic thyroid lesions (not subacute thyroiditis) are the most common cause of thyroid pain. As an example, sudden hemorrhage or hemorrhagic infarction of a solid thyroid nodule can result in a predominantly cystic and painful neck mass. Even relatively small hemorrhagic cysts of only 1 to 2 mL may be associated with considerable neck discomfort and dysphagia. More extensive hemorrhage may cause hoarseness and transient or permanent vocal cord paralysis and may compromise the airway, especially if the nodule is located within or below the thoracic inlet [2] (see "Clinical presentation and evaluation of goiter in adults", section on 'Obstructive symptoms'). In addition, chronic intermittent degeneration of a thyroid tumor can result in intermittent neck discomfort.

ETIOLOGY — True simple thyroid cysts (image 1) lined by benign epithelial cells are rare. As an example, in one ultrasound study of 1985 patients with 3483 nodules larger than 10 mm, there were only seven completely cystic nodules [3]. Most cystic nodules are partly solid structures that have undergone cystic degeneration (mixed or complex nodules) (image 2). Complex nodules are common. In a review of 1128 patients with 1458 thyroid nodules who underwent ultrasound-guided fine-needle aspiration (FNA), 53.5 percent were partially cystic, with 13.7 percent described as >75 percent cystic [4].

Thyroid adenomas and cancers — The majority of cystic thyroid nodules are benign, degenerating thyroid adenomas. Autonomously functioning thyroid adenomas are more likely to undergo cystic degeneration than nonfunctioning adenomas. Purely cystic lesions rarely contain cancer, but the likelihood of cancer in complex (cystic and solid) nodules approaches that of solid nodules (5 to 10 percent) [3,5-9]. The likelihood of cancer being present decreases as the proportion of the nodule that is cystic increases. In the ultrasound study described above, cancer was present in 5.8, 2.3, and 0 percent of mixed solid and cystic (25 to 74 percent cystic), predominantly cystic (>75 percent cystic), and completely cystic nodules, respectively [3]. In another report of 360 thyroid cancers, only nine (2.5 percent) had a cystic component that was >50 percent of the volume of the mass [10]. All nine of these cystic nodules showed other ultrasound features that suggested malignancy (microcalcifications, prominent mural solid component, irregular wall, increased vascularity).

Among the thyroid cancers that are associated with cysts, papillary thyroid cancer is most common [5], although cystic areas have been found in all types of thyroid cancer. In one surgical series of 71 cystic nodules of the thyroid, the following distribution was noted [5]:

●4 percent were simple cysts

●82 percent were degenerating adenomas

●14 percent were cancers, all papillary cancers

In assessing these figures, it is important to note that surgical series have selection bias. In this series, 23 percent of all nodules were cancers, approximately four to five times higher than in unselected patients with thyroid nodules [11,12]. If this correction is applied to the preceding results, the risk of cancer in unselected patients with cystic nodules can be estimated to be approximately 2 to 4 percent.

Thyroglossal duct cysts — The thyroid gland originates in the fetus in the foramen cecum at the base of the tongue and migrates caudally in the midline to its normal position in the anterior neck below the cricoid cartilage. This migration results in formation of the thyroglossal duct, which initially connects the floor of the pharynx to the thyroid gland. The thyroglossal duct normally disappears, but persistence of the duct can give rise to cystic masses. Over one-half of these cysts come to clinical attention during childhood and adolescence, but some first appear in adults.

Over 90 percent of thyroglossal duct cysts are midline, but some may be displaced slightly. Most occur below the hyoid bone, but they can occur anywhere along the thyroglossal duct. Cysts in the upper tract may move when the tongue is protruded.

Thyroglossal duct cysts may drain into the pharynx, become infected because of continuity with the pharynx, form sinus tracts to the overlying skin, and may rarely be malignant (usually a papillary thyroid cancer) [13]. For these reasons, symptomatic thyroglossal duct cysts should be excised [14]. (See "Thyroglossal duct cyst, thyroglossal duct cyst cancer, and ectopic thyroid".)

An analysis of FNAs and pathology from 86 suspected thyroglossal duct cysts at a referral center demonstrated the following [15]:

●26 percent were cystic, 12 percent cystic with septations, 32 percent mixed cystic and solid, and 30 percent were cystic or solid with debris.

●95 percent had benign FNA, 2 percent atypical, and 3 percent malignant.

●Benign features were proteinaceous material or histiocytes (63 percent for each), colloid (37 percent), squamous cells (35 percent), columnar cells (32 percent), follicular cells 15 percent), inflammatory cells and multinucleate giant cells (9 percent for each).

●75 percent of benign lesions were true thyroglossal duct cysts, the rest were epidermoid cysts, colloid nodules, and thyroiditis.

Hydatid cysts — Primary echinococcal cysts of the thyroid have been reported but are extremely rare [16].

Other — Other neck cysts, which may be confused with thyroid cysts, include the following:

●Parathyroid cysts – Parathyroid cysts are rare. Aspiration of clear, watery fluid from a neck mass is virtually diagnostic of a parathyroid cyst, which can be confirmed by finding a high concentration of parathyroid hormone in the cyst fluid [17]. (See "Parathyroid cysts".)

●Cystic hygromas – Cystic hygromas develop when the jugular lymph sac fails to communicate with the thoracic duct. These cysts usually present in early childhood. Unlike thyroid and thyroglossal duct cysts, cystic hygromas do not move with swallowing.

●Branchial cleft cysts – Branchial cleft cysts develop from the first, second, or third pharyngeal pouches and are usually located in the upper lateral neck (figure 1). They do not move with swallowing. (See "Differential diagnosis of a neck mass", section on 'Branchial cleft cyst'.)

EVALUATION — The clinical importance of the cystic thyroid nodule evaluation is primarily related to the need to exclude thyroid cancer. As noted above, purely cystic lesions (image 1) rarely contain cancer, but the likelihood of cancer in complex (cystic and solid) nodules approaches that of solid nodules, in the range of 5 to 10 percent [3,5,6]. It is the nature of the solid component associated with the "cyst" that is of primary clinical importance. The solid component may comprise more than one-half of the nodule, be just a small mass of cells along the wall of the cyst (image 2), or be just a thickening of the cyst wall [18].

As with thyroid nodules in general, the diagnostic evaluation of cystic thyroid nodules includes measurement of serum thyroid-stimulating hormone (TSH), assessment of the sonographic features, and, if indicated, fine-needle aspiration (FNA) biopsy. Features of the evaluation that are unique to patients with cystic nodules are reviewed below. The diagnostic approach to thyroid nodules in general is reviewed separately. (See "Diagnostic approach to and treatment of thyroid nodules".) (Related Pathway(s): Thyroid nodules: Initial evaluation in adults and Thyroid nodules: Initial evaluation in pregnant patients.)

Serum TSH — Most cystic thyroid nodules are nonfunctioning, and therefore the serum thyroid-stimulating hormone (TSH) is typically normal. Rarely, hemorrhage into a thyroid nodule can result in transient thyrotoxicosis in patients with previously normal TSH [19]. In addition, some cystic nodules are hyperfunctioning thyroid adenomas that have undergone cystic degeneration. In these settings, the TSH may be below normal. If the serum TSH concentration is low, indicating overt or subclinical hyperthyroidism, the possibility that the nodule is hyperfunctioning is increased, and thyroid scintigraphy should be performed next. (See 'Thyroid scintigraphy' below.)

Thyroid ultrasonography — Thyroid ultrasonography should be performed in all patients with a suspected thyroid nodule on physical examination or with nodules incidentally noted on other imaging studies (carotid ultrasound, computed tomography [CT], magnetic resonance imaging [MRI], or fludeoxyglucose [FDG]-positron emission tomography [PET] scan). Ultrasound can identify predominantly cystic nodules. In addition, there are several ultrasonographic findings that are suspicious for thyroid cancer (table 1). The predictive value of these characteristics varies widely, and we do not rely on thyroid ultrasound to diagnose cancer or to select patients for surgery. However, ultrasound findings can be used to select nodules for FNA biopsy. (See "Overview of the clinical utility of ultrasonography in thyroid disease", section on 'Criteria for identifying cancer'.)

Fine-needle aspiration

Indications — The presence of suspicious ultrasound features is more predictive of malignancy than nodule size alone. The decision to biopsy a thyroid nodule should be based upon a combination of ultrasonographic features and nodule size. This approach is consistent with the American Thyroid Association (ATA) guidelines (table 2) [20] and the American College of Radiology (ACR)-Thyroid Imaging Reporting and Data System (TIRADS) (table 3) [21]. (See "Overview of the clinical utility of ultrasonography in thyroid disease", section on 'Criteria for identifying cancer' and "Diagnostic approach to and treatment of thyroid nodules", section on 'Sonographic criteria for FNA'.)

For patients with mixed cystic-solid nodules without suspicious features on ultrasound, we perform FNA biopsy if the nodules are ≥2 cm (table 2). In the presence of suspicious ultrasound features, we perform FNA biopsy of mixed nodules ≥1.5 to 2 cm, or if the solid component exceeds 1 to 1.5 cm (0.5 cm for high-risk patients). Purely cystic nodules (no mural component) do not require a diagnostic FNA biopsy. Diagnostic biopsy usually requires tissue obtained from the solid component of the nodule, but occasionally, malignant cells are present in the cyst fluid. A complete discussion of thyroid biopsy techniques is reviewed elsewhere. (See "Thyroid biopsy".)

Ultrasound-guided FNA — The diagnostic accuracy of FNA performed by palpation is reduced in nodules with >25 to 50 percent cystic component [4,22]. Thus, we suggest ultrasound-guided FNA for predominantly cystic nodules. Thyroid cyst fluid may contain diagnostic follicular cells, macrophages, blood, and/or colloid (image 3). Thus, the cyst fluid should be assessed for cellular material. When ultrasonography shows a solid component that is either small or posteriorly located, ultrasound-guided FNA directed at the solid component or the cyst wall may reduce the risk of a nondiagnostic result. (See "Thyroid biopsy", section on 'Ultrasound guidance'.)

Nondiagnostic FNA results — Cyst fluid may be acellular, or the cellular material may be degenerated and uninterpretable by the cytopathologist. A finding of no malignant cells in the cyst fluid may be reassuring if the nodule is primarily cystic and decreases in size after aspiration. However, if palpation-guided FNA is performed and is nondiagnostic and the nodule remains palpable, we suggest repeat aspiration under ultrasound guidance.

In a series of 112 cystic nodules with surgical confirmation, malignancy was found at surgery in only 1 of 70 nodules (1.4 percent) that resolved after aspiration versus 4 of 37 nodules (10.8 percent) that remained palpable after aspiration [23]. After an initial nondiagnostic FNA, repeat FNA with ultrasound guidance will provide a diagnostic specimen in 50 percent of cystic nodules [4].

When the results of ultrasound-guided FNA of a complex cystic nodule are nondiagnostic and the nodule remains palpable after aspiration, repeat aspiration under ultrasound guidance is indicated.

Several caveats should be kept in mind:

●For nondiagnostic hemorrhagic nodules, it may be helpful to wait four weeks for the nodule to organize and the blood to be resorbed before attempting a follow-up biopsy.

●Atypical cells may be present in aspirates of thyroid cysts. The cytologic features of reparative epithelial cyst-lining cells may include nuclear grooves and granular cytoplasm, but these are distinguished from papillary cancers by their spindled cytomorphology and other characteristic features [24].

●The nature of the fluid may be helpful. The fluid from nodules that contain cancer is usually hemorrhagic or pink-colored [25]. Chocolate-colored fluid suggests hemorrhage that occurred at least one week before aspiration. Straw-colored fluid is less likely to be associated with cancer (although the fluid was straw-colored in one cystic papillary cancer in the series noted above [5]); furthermore, cysts containing straw-colored fluid are more likely to resolve after aspiration [5].

●Colloid cysts (image 3) may contain viscous, yellow-brown fluid that cannot be aspirated through a 25-gauge needle but may be slowly aspirated through a 22-gauge or larger needle. The cytology of cells from the solid component of complex colloid nodules is usually consistent with a benign macrofollicular or colloid adenoma; if the cyst fluid is acellular but composed predominantly of colloid in such a lesion, it is likely to be benign.

Thyroid scintigraphy — Thyroid scintigraphy should be performed in patients with a low serum TSH concentration. Predominantly cystic nodules and the cystic component of complex nodules do not concentrate radioiodine or technetium and will appear hypofunctioning ("cold") on radionuclide scans. However, some cystic nodules are degenerating, autonomously functioning thyroid adenomas. A thyroid scan may demonstrate that the solid portion of the nodule is autonomous in a patient with a low serum TSH concentration and a complex nodule, or a patient with a complex nodule in whom the aspiration cytology shows microfollicular cytology ("follicular neoplasm"). A nodule that is hyperfunctioning on radioiodine imaging does not require FNA, because autonomous nodules are rarely cancer. (See "Diagnostic approach to and treatment of thyroid nodules", section on 'Thyroid scintigraphy'.)

MANAGEMENT — Several approaches may be successful in managing patients with cystic thyroid nodules. Fine-needle aspiration (FNA) alone may be curative in a minority of patients. Cancer is uncommon in cystic nodules that are no longer palpable after aspiration or substantially resolve on ultrasound [23]. If the nodule remains palpable after aspiration or persists on ultrasound, however, treatment depends upon the cytologic results obtained from FNA. There are six major categories of results that are obtained from FNA, each of which indicates different subsequent management. The management of cytologically nondiagnostic and benign cystic nodules is reviewed here. The other diagnostic categories and subsequent management are reviewed in detail separately. (See "Diagnostic approach to and treatment of thyroid nodules", section on 'Management' and "Thyroid biopsy", section on 'Diagnostic categories'.)

Thyroxine (T4, levothyroxine) therapy was not beneficial in a small, randomized trial of patients with cystic nodules (recurrences occurred in seven patients (70 percent) in both the placebo and thyroid hormone-treated groups) [26]. Thus, there is no role for thyroxine suppressive therapy in patients with cystic nodules.

Nondiagnostic cystic nodules — Cytologically nondiagnostic cysts with a significant solid component require repeat diagnostic ultrasound-guided FNA. Repeat aspiration may also be therapeutic. If repeated ultrasound-guided aspirations of a predominately cystic nodule are nondiagnostic and the nodule remains palpable or persists on ultrasound after aspiration, or rapidly accumulates fluid, ultrasound monitoring or surgery are management options. Ultrasound monitoring is typically performed every 6 to 18 months and then possibly less often (three to five years) if the nodule size is stable or smaller. We prefer surgical resection if the cytology is nondiagnostic and the size of the solid component is greater than 1.5 cm (greater than 1 cm with suspicious ultrasonographic characteristics) (table 1).

Benign cystic nodules

Initial treatment: Re-aspiration — Cytologically benign cysts do not require re-aspiration unless it is to alleviate compressive symptoms. Up to 25 to 50 percent of predominantly cystic nodules disappear after aspiration, but fluid reaccumulates in the majority due to either recurrent hemorrhage or slow accumulation of fluid [5,27]. Repetitive aspiration is preferred over surgery by some patients, and some cysts do not recur after several aspirations. Cysts that are tense and hard on physical examination are more likely to refill after aspiration.

Persistent fluid reaccumulation — If the nodule recurs after repeated aspirations and there is continued enlargement or pain associated with fluid reaccumulation, we suggest surgical excision or percutaneous interventional ultrasound-guided therapy (if expertise is available) (algorithm 1). The choice should be individualized based on nodule characteristics, patient preferences, and advantages and disadvantages of the procedures (table 4).

Surgery — Despite benign cytology, many patients opt for surgical excision of cystic nodules if the nodule recurs after one or more successful aspirations or if there is continued enlargement or pain associated with fluid reaccumulation. Size (>4 cm) of the cystic nodule may also be used as a criterion for surgery, although we do not use size as an absolute criteria for surgery if the patient is not bothered by the nodule.

Thyroid lobectomy is sufficient for definitive treatment of a predominately cystic nodule, but the extent of surgery may be influenced by the presence of contralateral thyroid nodules.

Percutaneous interventional ultrasound-guided therapy — Cystic thyroid nodules can be treated by ultrasound-guided injection of ethanol or sclerosing agents and by ultrasound-directed physical energy. In countries where these procedures are performed routinely, they are alternatives to surgery [28]. Initially, these approaches did not gain widespread acceptance in the United States because of potential complications, including occasional reports of prolonged pain after the procedure. However, they are being used with increasing frequency in the United States.

If a nonsurgical option is preferred, the American Thyroid Association (ATA) statement on the use of ablation techniques for benign thyroid nodules suggests ethanol ablation when the solid component is less than 20 percent, and radiofrequency ablation (RFA) when the solid component is larger (algorithm 1) [29]. Another approach is to use ethanol for the cystic component and RFA salvage treatment of the solid component [29,30].

A meta-analysis of 19 studies comparing ethanol ablation with other non-surgical modalities found similar volume reduction and success rates for ethanol ablation and RFA for cystic thyroid nodules. However, RFA is more expensive, requires more sessions, and was associated with more pain during and following the procedure. The major complication rate for ethanol ablation was 0.5 percent [31]. Of note, ethanol is considerably less effective than RFA at reducing the solid portion of a complex cystic and solid nodule [30,31].

●Ethanol ablation – Ethanol ablation generally involves removing as much of the cyst fluid as possible under ultrasound guidance and then instilling an amount of 99 percent ethanol equal to 50 percent of the aspirated volume into the thyroid cyst cavity. In some series, the ethanol is removed after five minutes, and in other reports, the fluid is allowed to remain in the cyst cavity. In randomized trials, ethanol ablation effectively reduces the size of benign cystic thyroid nodules [32-34]. As examples:

•In a randomized trial of FNA of the cyst fluid versus FNA followed by percutaneous ethanol injection in 281 patients, median reduction in cystic nodule volume after one year was significantly greater in the ethanol group (85.6 versus 7.3 percent) [34]. Compressive and cosmetic symptoms were also significantly improved in the ethanol group.

•Another randomized trial compared flushing with 99 percent ethanol versus saline in 66 patients with recurrent thyroid cysts (≥2 mL) [33]. All patients had subtotal cyst aspiration prior to flushing and subsequent complete fluid aspiration after flushing. After six months, cure (defined as a cyst volume less than 1 cm) was obtained in a significantly greater proportion of patients treated with ethanol (82 versus 48 percent). Six patients required more than one ethanol ablative procedure.

The results of observational trials are similar [35-37]. In one prospective study, only 6 of 92 patients who responded to ethanol injections relapsed after a nine-year follow-up [32], but the recurrence rate was as high as 24 to 28 percent in other studies [35,38]. Size over 20 mL and vascularity were predictors of recurrence [38].

Ethanol has been used successfully in patients with thyroglossal duct cysts [30,39]; in one study, 95 percent reduction in volume after one treatment was seen a year later [39].

Pain during and immediately after the procedure is the major side effect of ethanol ablation. In one study, 21 percent of patients had transient moderate to severe pain [33]. Recurrent laryngeal nerve palsy also has been reported [40]. As a result, ethanol should always be administered under ultrasound guidance. Where ethanol ablation is performed routinely, it is an alternative to surgery. In a survey of the European Thyroid Association, 41 percent recommended ethanol ablation and 36 percent surgery (difference not statistically significant) for a recurrent 4 cm thyroid cyst in a young woman [41].

●RFA – Ultrasound-guided RFA has also been used to reduce the volume of benign, cystic thyroid nodules [42,43]. In one study, 20 patients with predominantly cystic nodules and incomplete resolution of symptoms after ethanol ablation underwent RFA. RFA after a single session of ethanol ablation significantly reduced mean symptom score, cosmetic score, and nodule volume (mean nodule volume decreased from 11.3 to 0.9 mL) [44]. Two patients required more than one RFA session. The major side effect of RFA is pain and/or a burning sensation in the neck radiating to the head, shoulders, teeth, and chest. Hematoma, skin burns, and transient voice changes have also been reported.

RFA of thyroid nodules was first used in 2002. The procedure was not approved in the United States until 2018, and therefore, RFA has not been commonly used in the United States. Many centers in the United States are establishing RFA programs, and it is likely that RFA will be used increasingly as expertise in the technique is developed [45,46].

●Other ultrasound-guided therapies

•Interstitial laser photocoagulation – Ultrasound-guided interstitial laser photocoagulation (percutaneous laser ablation) has also been used to treat cystic nodules. In a randomized trial, 15 of 22 (68 percent) patients undergoing interstitial laser photocoagulation had a reduction in cyst size to less than 1 mL versus 4 of 22 (18 percent) in the group that received aspiration alone [47]. Laser photocoagulation has also been used to treat benign nodular thyroid disease, including autonomous nodules [48,49] (see "Treatment of toxic adenoma and toxic multinodular goiter", section on 'Other therapies'). This technique is not commonly performed in the United States.

•Polidocanol sclerotherapy – The sclerosing agent polidocanol has been used in China as an alternative to ethanol, reducing nodule size by more than 70 percent in essentially all patients (average cyst size 15.6 mL but some as large as 139 mL). Adverse effects included mild pain (17.5 percent) and fever (12.3 percent) [50]

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Thyroid nodules and cancer".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Thyroid nodules (The Basics)")

●Beyond the Basics topics (see "Patient education: Thyroid nodules (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Clinical presentation – Cystic thyroid nodules often come to attention when noted by the patient or as an incidental finding during a routine physical examination or radiologic procedure, such as carotid ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI) of the neck. However, some patients have symptoms, such as neck pain and dysphagia. (See 'Clinical presentation' above.)

●Etiology – The majority of cystic thyroid nodules are benign, degenerating thyroid adenomas (image 2). However, thyroid cancers may be cystic. (See 'Etiology' above.)

●Evaluation – As with thyroid nodules in general, the diagnostic evaluation of cystic thyroid nodules includes measurement of thyroid-stimulating hormone (TSH), assessment of the sonographic features, and, if indicated, fine-needle aspiration (FNA) biopsy. (See 'Evaluation' above.)

•FNA – Purely cystic nodules (no mural component) do not require a diagnostic FNA biopsy. For patients with mixed cystic-solid nodules without suspicious features on ultrasound, we perform FNA biopsy if the nodules are ≥2 cm (table 2 and table 3). In the presence of suspicious ultrasound features, we perform FNA biopsy of mixed nodules ≥1.5 to 2 cm or if the solid component exceeds 1 to 1.5 cm (0.5 cm for high-risk patients). (See 'Fine-needle aspiration' above.)

●Treatment – Aspiration alone may be curative in a minority of patients. If the nodule remains palpable after repeated ultrasound-guided aspirations, however, treatment depends upon the cytologic results obtained from FNA. (See 'Management' above and "Diagnostic approach to and treatment of thyroid nodules", section on 'Management'.)

•Nondiagnostic cytology – If repeated ultrasound-guided aspirations of a predominately cystic nodule are nondiagnostic, and the size of the solid component is greater than 1.5 cm (greater than 1 cm with suspicious ultrasonographic characteristics) (table 1), we suggest surgical resection (Grade 2C). Ultrasound monitoring may be an alternative option depending on the ultrasound findings. Ultrasound monitoring is typically performed every 6 to 18 months and then possibly less often (three to five years) if the nodule size is stable or smaller. (See 'Nondiagnostic cystic nodules' above.)

•Benign cytology – Cytologically benign cysts do not require re-aspiration unless it is to alleviate compressive symptoms. If the nodule recurs after repeated aspirations and there is continued enlargement or pain associated with fluid reaccumulation, we suggest surgical excision or percutaneous interventional ultrasound-guided therapy (if expertise is available) rather than persisting with re-aspiration (algorithm 1) (Grade 2C). The choice should be individualized based on nodule characteristics, patient preferences, and advantages and disadvantages of the procedures (table 4). Ethanol ablation is most efficacious when the solid component of a cystic nodule is <20 percent. Initial ethanol ablation of the cystic component may be followed by salvage RFA of the solid component. (See 'Benign cystic nodules' above and 'Percutaneous interventional ultrasound-guided therapy' above.)