Thyroid Tumors

Thyroid tumors in horses encompass neoplastic growths arising from the thyroid gland, a pair of endocrine organs located along the trachea in the cranial cervical region that produce hormones essential for regulating metabolism, growth, and development. These tumors range from benign adenomas, which are the most common type, to more aggressive carcinomas with potential for local invasion and metastasis. Understanding thyroid tumors is important for horse owners because these growths may be visible or palpable as neck masses and can potentially affect swallowing, breathing, or thyroid hormone production depending on their size and location. Early recognition and appropriate veterinary evaluation ensure optimal management and outcomes.

Thyroid tumors occur with moderate frequency in horses, representing a notable percentage of equine endocrine neoplasms, with incidence increasing in older animals. Thyroid adenomas comprise the majority of cases and typically behave in a benign fashion, growing slowly and remaining localized to the thyroid region. Thyroid carcinomas, while less common, carry more serious implications due to their potential for invasive growth and metastatic spread. The condition affects horses of various breeds without strong predilection, though senior horses over fifteen years of age represent the highest-risk population. Both male and female horses develop thyroid tumors, with no consistent sex predilection documented.

The impact of thyroid tumors on equine health varies considerably based on tumor type, size, and hormonal activity. Many thyroid tumors are discovered as incidental findings during routine examination, causing minimal clinical effects. Larger tumors may cause visible or palpable neck enlargement, potentially progressing to compress the trachea or esophagus and cause respiratory or swallowing difficulties. Functional tumors that produce excess thyroid hormones can cause hyperthyroidism, though this is relatively uncommon in horses compared to other species. Performance effects may include subtle changes in metabolism, weight, or exercise tolerance depending on hormonal activity and tumor location.

Treatability of thyroid tumors in horses is generally favorable, particularly for benign adenomas that can be surgically excised with excellent outcomes. Thyroid carcinomas require more aggressive treatment approaches and carry more guarded prognoses, particularly if metastatic spread has occurred. Horses can function normally with partial or complete thyroid removal, though some may require thyroid hormone supplementation following bilateral thyroidectomy. Early detection of thyroid tumors as small, localized masses enables less invasive surgical approaches and better outcomes. Regular veterinary examinations that include careful palpation of the neck region facilitate early tumor detection.

The primary causes of thyroid tumor development in horses involve cellular mutations within thyroid tissue that lead to uncontrolled proliferation and tumor formation. These mutations may affect genes controlling cell growth, division, and differentiation, though specific genetic alterations driving equine thyroid tumorigenesis remain incompletely characterized. Follicular cells that produce thyroid hormones are the origin of most thyroid tumors, with neoplastic transformation likely occurring through accumulated genetic damage over time. Parafollicular C-cells, which produce calcitonin, can also undergo neoplastic transformation, though this is less common. The specific triggers initiating these cellular changes are not well defined in horses.

Genetic and breed predisposition for thyroid tumors has not been established in horses through controlled studies or large-scale genetic investigations. Unlike some human thyroid tumors with identified hereditary patterns and specific genetic mutations, equine thyroid neoplasia appears to occur sporadically without clear familial clustering. Individual genetic variation likely influences tumor susceptibility, but no specific genetic markers have been identified for equine thyroid tumor risk. Various breeds appear in case reports and case series, but distributions likely reflect regional population demographics rather than true breed predisposition. Large-scale studies specifically investigating genetic factors in equine thyroid tumors are lacking.

Environmental and management factors potentially influencing thyroid tumor development in horses are not well characterized. Iodine nutrition has theoretical relevance given iodine's essential role in thyroid hormone production, though direct links between dietary iodine and equine thyroid tumors have not been established. Chronic goitrogenic exposures that stimulate thyroid activity could theoretically promote tumor development, but specific associations are unproven. Radiation exposure affects thyroid tumor risk in other species, though environmental radiation sources affecting horses are generally minimal. Geographic factors including regional iodine availability could potentially influence thyroid health over generations without specifically causing tumors.

Risk factors for thyroid tumors primarily include advanced age, with the majority of cases occurring in horses over fifteen years old. The accumulated cellular damage and reduced immune surveillance associated with aging likely contribute to increased tumor development. Chronic thyroid gland stimulation from any cause could theoretically promote neoplastic change, though this mechanism is speculative in horses. Prior thyroid inflammation or disease might predispose to later tumor development. No specific modifiable risk factors have been definitively identified that would enable targeted prevention strategies for thyroid tumors in horses.

The pathophysiology of thyroid tumor development involves progressive neoplastic transformation and growth of thyroid cells. Adenomas develop as encapsulated masses that expand within the thyroid gland without invading surrounding tissues. These benign tumors may grow slowly over months to years, reaching substantial size before causing clinical effects. Carcinomas demonstrate invasive growth characteristics, potentially extending into surrounding cervical tissues, blood vessels, and lymphatics. Metastatic spread of carcinomas may involve regional lymph nodes and distant organs including lungs. Functional tumors produce thyroid hormones autonomously, unregulated by normal feedback mechanisms, potentially causing hyperthyroidism. Compression of adjacent structures including the trachea and esophagus occurs as tumors enlarge regardless of malignant potential.

Early warning signs of thyroid tumors in horses are often absent or extremely subtle, with many tumors remaining clinically silent until reaching substantial size. Owners or caretakers performing regular grooming or handling may notice subtle asymmetry or firmness in the throatlatch region before obvious masses develop. Very attentive owners might detect mild changes in neck contour or resistance to flexion of the head and neck. Horses may show subtle reluctance during bridling or having halters placed if tumors create early discomfort. Subtle changes in appetite, energy level, or coat quality could potentially relate to altered thyroid function, though these nonspecific signs are easily attributed to other causes. Regular veterinary examination remains the most reliable means of early detection.

Common symptoms of thyroid tumors become more apparent as masses enlarge and affect surrounding structures. Visible or palpable neck masses represent the most frequent presenting sign, with owners often noticing asymmetric swelling in the throatlatch area. Masses typically feel firm and may be freely movable or attached to underlying tissues depending on tumor characteristics. Weight changes, either loss or gain, may occur if tumors affect thyroid hormone production. Coat changes including poor quality, delayed shedding, or altered hair growth might reflect thyroid dysfunction. Progressive enlargement of masses over time distinguishes tumors from other causes of neck swelling.

Behavioral changes associated with thyroid tumors may reflect hormonal effects, physical discomfort, or progression of disease. Horses with hyperfunctional tumors producing excess thyroid hormone may display increased activity, nervousness, or excitability. Conversely, hypothyroid effects could cause lethargy, depression, or decreased activity. Changes in appetite, either increased or decreased, may accompany thyroid dysfunction. Reluctance to flex the neck or resistance to tack placement might indicate local discomfort from tumor growth. General attitude changes including depression or irritability may accompany chronic illness effects.

Physical signs detectable during veterinary examination include palpable thyroid masses of variable size, consistency, and mobility. Unilateral tumors cause asymmetric thyroid enlargement, while bilateral involvement produces more generalized cervical swelling. Tumors may be freely movable beneath the skin or fixed to underlying structures depending on invasiveness. Tracheal deviation might be palpable or visible with large unilateral masses. Respiratory stridor may be detected if tracheal compression is significant. Changes in skin overlying tumors, including heat, tension, or altered appearance, may develop with aggressive tumors. Enlarged cervical lymph nodes might indicate regional metastasis from carcinomas.

Symptom progression in thyroid tumor cases varies based on tumor type and growth rate. Benign adenomas typically enlarge slowly over months to years, with gradual progression of mass effects. Carcinomas may grow more rapidly and develop additional signs related to invasive behavior. Compression of adjacent structures produces progressive respiratory noise, swallowing difficulty, or jugular distension. Metastatic spread causes symptoms related to affected organs, potentially including respiratory signs from lung involvement. Functional tumors may cause progressively worsening hyperthyroid symptoms as tumor mass increases. Some tumors remain stable for extended periods before entering phases of more rapid growth.

Emergency symptoms requiring immediate veterinary attention include severe respiratory distress from tracheal compression or obstruction. Rapid tumor enlargement over days suggesting aggressive growth or hemorrhage into the tumor warrants urgent evaluation. Profound weakness, collapse, or signs of thyroid storm from excessive hormone production require emergency care. Inability to swallow or profuse salivation suggesting esophageal obstruction needs immediate assessment. Severe swelling with skin discoloration or breakdown indicates potentially complicated tumors. Any sudden deterioration in a horse with known thyroid tumor warrants emergency consultation.

Physical examination provides initial assessment of suspected thyroid tumors, with careful palpation of the cervical region forming the foundation of evaluation. Veterinarians assess the size, location, consistency, mobility, and bilateral versus unilateral nature of thyroid enlargement. The relationship of masses to surrounding structures including trachea, esophagus, and blood vessels is evaluated. Evidence of tracheal deviation, compression, or jugular distension is noted. General physical examination assesses body condition, vital parameters, and signs potentially related to thyroid dysfunction. Examination of regional lymph nodes evaluates for potential metastatic spread. History regarding duration of swelling, rate of growth, and associated symptoms guides diagnostic approach.

Diagnostic tests for thyroid tumor evaluation include bloodwork, imaging studies, and tissue sampling for definitive diagnosis. Thyroid hormone measurement, including total and free T4 levels, assesses functional status of the thyroid gland. Endogenous TSH measurement, when available, provides additional endocrine assessment. Complete blood count and biochemistry panels screen for systemic effects and overall health status. Ultrasonography of the thyroid region provides detailed imaging of tumor architecture, size, vascularity, and relationships to adjacent structures. Radiography may reveal tracheal deviation or compression from large masses. Advanced imaging may be indicated for comprehensive staging.

Advanced diagnostics including specialized imaging and tissue sampling provide definitive diagnosis and complete staging information. Computed tomography or magnetic resonance imaging offers detailed three-dimensional assessment of tumor extent, invasiveness, and potential metastatic spread. Nuclear scintigraphy using technetium pertechnetate evaluates thyroid tissue function and distribution, identifying hot nodules suggesting hyperfunctional tissue. Fine-needle aspiration cytology obtained from thyroid masses provides preliminary cellular characterization. Biopsy with histopathological examination of excised tissue provides definitive tumor identification and malignancy assessment. Thoracic imaging screens for pulmonary metastases in suspected carcinoma cases.

Differential diagnosis for cervical masses in the thyroid region includes various conditions requiring distinction from true thyroid neoplasia. Thyroid cysts, non-neoplastic fluid-filled structures, may cause thyroid enlargement. Thyroid hyperplasia, benign enlargement without neoplasia, can mimic tumor. Abscesses in the cervical region from Streptococcus equi or other infections create masses potentially confused with tumors. Salivary gland disease including mucoceles or tumors may occur in adjacent regions. Lymph node enlargement from various causes produces cervical masses requiring differentiation. Laryngeal or tracheal tumors may be confused with thyroid origin. Appropriate diagnostic testing enables accurate differentiation guiding treatment planning.

Emergency and immediate treatment for thyroid tumors is rarely required unless acute respiratory compromise or other crisis occurs. Horses with severe respiratory distress from tracheal compression may require emergency tracheostomy to bypass the obstruction. Corticosteroids may provide temporary reduction in peritumoral swelling while planning definitive treatment. Thyroid storm, though rare in horses, would require beta-blocker therapy, cooling measures, and supportive care. Acute hemorrhage into tumors causing rapid enlargement may necessitate emergency surgical intervention. Most thyroid tumor cases allow time for complete diagnostic evaluation and planned surgical treatment rather than emergency intervention.

Medical management options for thyroid tumors are limited, as surgery provides definitive treatment for most cases. Antithyroid medications such as methimazole may be used temporarily to control hyperthyroidism from functional tumors while awaiting surgery or when surgery is not feasible. Radioactive iodine therapy, used in some species for thyroid tumors, is not routinely available or practical for horses. Medical management does not address the underlying tumor and serves primarily to control symptoms or prepare for surgical intervention. Non-surgical approaches may be appropriate for elderly horses with slowly growing benign tumors causing minimal effects. Palliative care focuses on comfort when definitive treatment is not pursued.

Surgical options provide definitive treatment for thyroid tumors, with approach determined by tumor characteristics and laterality. Unilateral thyroidectomy removes the affected thyroid lobe while preserving the contralateral gland, maintaining thyroid hormone production. This approach is appropriate for tumors limited to one thyroid lobe and represents the most common surgical treatment. Bilateral thyroidectomy removes both thyroid lobes and is necessary when both glands are affected, requiring lifetime thyroid hormone supplementation afterward. Careful surgical technique preserves the parathyroid glands and recurrent laryngeal nerves located near the thyroid. Aggressive resection with adequate margins is essential for carcinomas to minimize recurrence risk. Metastasectomy, removal of metastatic lesions, may be considered in selected cases.

Supportive care during thyroid tumor treatment addresses hormonal balance, surgical recovery, and nutritional needs. Post-operative care following thyroidectomy includes incision management, pain control, and monitoring for complications. Calcium monitoring is essential following bilateral thyroidectomy due to potential parathyroid compromise. Thyroid hormone supplementation begins after bilateral thyroid removal, with dose adjustments based on hormone level monitoring. Nutritional support maintains body condition during treatment and recovery. Monitoring for hyperthyroid symptoms resolves following removal of functional tumors. Antibiotics may be prescribed to prevent surgical site infection.

Rehabilitation and return to work following thyroid surgery progresses based on surgical extent and individual healing. Incision healing typically requires two to three weeks of rest and monitoring. Gradual return to activity follows confirmation of uncomplicated healing. Horses requiring thyroid supplementation need stable hormone levels before resuming work. Most horses return to previous activity levels following successful unilateral thyroidectomy. Those requiring bilateral thyroidectomy may need ongoing monitoring to optimize supplementation during return to work. Performance horses may require adjustment periods as metabolism normalizes following tumor removal.

Treatment decision factors include tumor type and behavior, surgical feasibility, the horse's overall condition, and owner goals. Benign adenomas warrant surgical removal for cosmetic concerns, to prevent complications from continued growth, or when functional tumors cause symptoms. Carcinomas require aggressive treatment given malignant potential, with honest prognosis discussions regarding outcomes. The horse's age and general health influence surgical risk assessment. Owner preferences regarding treatment intensity and financial investment guide decision-making. Location and size of tumors affect surgical complexity and risk. Availability of surgical expertise influences treatment options and outcomes.

Recovery timeline following thyroid surgery varies based on surgical extent, tumor characteristics, and individual healing response. Uncomplicated unilateral thyroidectomy typically requires two to four weeks of rest before gradual return to activity. More extensive surgery involving bilateral thyroidectomy or resection of invasive tumors may require longer recovery periods. Initial post-operative focus addresses incision healing, pain management, and monitoring for complications. Horses requiring thyroid hormone supplementation need time for dose optimization before resuming normal activity. Full return to previous work levels typically takes four to eight weeks following uncomplicated surgery.

Post-treatment care and monitoring protocols ensure optimal recovery and early detection of complications or recurrence. Incision monitoring identifies infection, dehiscence, or seroma formation requiring intervention. Temperature monitoring detects post-surgical fever suggesting complications. Blood calcium monitoring is essential following bilateral thyroidectomy or when parathyroid preservation is uncertain. Thyroid hormone levels guide supplementation adjustment in horses requiring replacement therapy. Periodic examination of the surgical site monitors for tumor recurrence. Follow-up ultrasound or imaging evaluates for local recurrence or metastatic development in carcinoma cases. Long-term monitoring continues for one to two years following malignant tumor treatment.

Prognosis factors influence expected outcomes and help establish realistic expectations for horse owners. Tumor type represents the primary prognostic indicator, with benign adenomas carrying excellent prognoses following complete excision. Carcinomas have more variable outcomes depending on stage at diagnosis, completeness of resection, and presence of metastasis. Tumor size affects surgical complexity and risk, favoring smaller tumors. Early detection before complications develop improves outcomes. Complete surgical margins predict lower recurrence rates for malignant tumors. The horse's overall health and age affect surgical survival and recovery quality. Presence of metastatic disease at diagnosis substantially worsens prognosis for carcinomas.

Long-term soundness outlook following thyroid tumor treatment is excellent for the majority of benign adenoma cases. Horses with completely excised adenomas typically have normal life expectancy and function. Carcinoma cases have more variable long-term outcomes, with some horses achieving sustained remission while others experience recurrence. Horses requiring thyroid hormone supplementation following bilateral thyroidectomy can maintain normal function with appropriate management. Performance horses may return to previous athletic levels following uncomplicated recovery. Quality of life assessment guides ongoing management, with humane euthanasia appropriate when comfort cannot be maintained in cases of progressive malignant disease.

Management practices that support thyroid health and general wellness represent the only available approach to thyroid tumor prevention given the absence of identified specific preventable causes. Appropriate iodine nutrition, neither deficient nor excessive, supports normal thyroid function, though direct tumor prevention benefits are unproven. Minimizing exposure to known goitrogenic substances, when identifiable, represents prudent management. Regular veterinary care including thorough physical examination enables early detection of developing thyroid enlargement. General health management supporting immune function and reducing chronic disease burden may contribute to overall cancer resistance. Stress reduction through appropriate housing and management supports physiological homeostasis.

Nutritional prevention recommendations focus on providing balanced diets with appropriate iodine content and overall nutritional adequacy. Iodine requirements for horses are met through most commercial feeds and forages in many geographic regions. Iodized salt blocks or supplements provide additional iodine when indicated by regional deficiency. Avoiding excessive iodine supplementation is important, as iodine excess can also affect thyroid function. Quality forage and balanced concentrate feeding support overall health. Adequate trace mineral nutrition including selenium supports cellular health and potentially immune function. Avoiding feed contamination with goitrogenic substances protects thyroid health.

Exercise and conditioning recommendations aim to maintain overall fitness and health that may support disease resistance. Regular appropriate exercise maintains cardiovascular health, proper body condition, and metabolic function. Consistent conditioning supports physiological resilience throughout the horse's lifespan. Avoiding excessive training stress helps maintain immune competence. Age-appropriate activity levels respect changing needs as horses mature and age. Balance between activity and recovery optimizes overall health and wellbeing.

Environmental factors relevant to general health and potentially thyroid function include housing quality, pasture management, and exposure minimization. Clean, well-maintained facilities reduce overall disease and stress exposure. Pasture management avoiding toxic plants and contamination supports health. Some plants have goitrogenic properties that could theoretically affect thyroid health if consumed in large quantities. Water quality should be adequate with appropriate mineral content. Environmental radiation exposure is generally minimal for horses but represents a theoretical thyroid health consideration.

Health monitoring protocols enabling early thyroid tumor detection include regular veterinary examinations with thorough cervical palpation. Annual or semi-annual wellness examinations should include careful assessment of the thyroid region bilaterally. Owners should become familiar with normal throatlatch anatomy to recognize developing asymmetry or masses. Baseline thyroid hormone measurement in senior horses provides reference values for comparison if symptoms develop. Prompt veterinary evaluation of neck swelling, respiratory changes, or metabolic abnormalities enables earlier diagnosis when thyroid tumors do develop.

Daily management adjustments for horses diagnosed with thyroid tumors depend on tumor size, location, hormonal activity, and treatment status. Feeding and watering should accommodate any swallowing difficulties, with feeds moistened if needed and water easily accessible. Monitoring appetite, water intake, and weight provides information about metabolic status and disease progression. Horses on thyroid hormone supplementation require consistent medication administration as prescribed. Temperature monitoring detects complications or infection. Daily observation notes any changes in mass size, respiratory effort, or general demeanor. Adjustments to management may be needed as the condition evolves or following treatment.

Housing and turnout considerations balance respiratory support with appropriate activity and social needs. Well-ventilated stabling protects respiratory function if tracheal compression affects breathing. Dust minimization through appropriate bedding and stable management supports respiratory health. Turnout provides fresh air and gentle exercise when the horse's condition permits. Extreme weather conditions that might stress the respiratory system should be avoided. Safe fencing and turnout areas prevent injuries that could complicate management. Companion horses provide social contact without creating stressful situations.

Exercise modifications depend on respiratory status, thyroid hormone levels, and overall condition. Horses with small non-functional tumors may continue normal activity without restriction. Exercise should be reduced if respiratory compromise from tracheal compression is present. Hyperthyroid horses may show increased heart rate and sweating during exercise, warranting reduced workload until treatment normalizes hormone levels. Post-surgical exercise follows veterinary guidance based on healing progress. Light work may be appropriate during medical management or when awaiting surgery. Monitoring for exercise intolerance, excessive sweating, or respiratory difficulty guides activity level decisions.

Monitoring and ongoing care requirements include regular assessment of tumor status, thyroid function, and overall condition. Owners should learn to visually and manually assess the thyroid region, noting changes in size or character. Thyroid hormone levels require periodic monitoring in horses with functional tumors or those receiving supplementation. Body weight tracking identifies concerning trends in either direction. Behavioral changes suggesting thyroid dysfunction or discomfort warrant veterinary consultation. Post-treatment monitoring follows veterinary recommendations for detecting recurrence. Communication between owner and veterinary team ensures appropriate management adjustments.

Quality of life and use considerations guide ongoing management decisions throughout the disease course. Most horses with thyroid tumors maintain good quality of life, particularly with benign slow-growing tumors or following successful treatment. Objective assessment of comfort, appetite, respiratory function, and engagement with environment evaluates quality of life. Some horses continue normal work while others require activity modifications based on tumor effects. Treatment success determines long-term functional capacity and use potential. Humane euthanasia becomes appropriate when quality of life cannot be maintained despite therapeutic efforts. End-of-life planning discussions before crisis situations reduce stress when difficult decisions become necessary.

High-risk breeds for thyroid tumors have not been definitively established, as this condition appears to affect horses across all breeds without consistent predilection. Various breeds appear in case reports reflecting population demographics rather than true genetic susceptibility. Thoroughbreds, Quarter Horses, Warmbloods, and Arabian horses appear in reports proportional to their general population representation. Draft breeds and pony breeds develop thyroid tumors without elevated or reduced frequency compared to other horses. No breeding practices or genetic selection criteria have been established to reduce thyroid tumor risk. The lack of identified breed predisposition suggests that other factors, particularly age, play more significant roles in tumor development than breed genetics.

Use and discipline considerations do not appear to influence thyroid tumor development, though they may affect detection timing and presentation. Performance horses receiving regular veterinary attention and physical handling may have thyroid abnormalities detected earlier than horses with less frequent professional evaluation. Horses in disciplines requiring precise tack fitting might have neck masses noticed during equipment adjustment. Breeding stallions and broodmares examined regularly during reproductive evaluations may have incidental thyroid findings detected. All horses regardless of use benefit from regular veterinary examination including thorough palpation of the thyroid region. Detection bias likely explains any apparent differences in incidence across use categories.

Genetic testing and breeding recommendations specific to thyroid tumor prevention are not available or indicated based on current understanding. General recommendations for breeding healthy horses apply, with selection based on overall soundness and freedom from heritable disease. Horses treated for benign thyroid tumors can be bred normally if otherwise suitable breeding candidates. Those treated for carcinomas should be evaluated individually regarding breeding decisions based on prognosis and potential hereditary factors. Current knowledge does not support genetic selection against thyroid tumors. Ongoing research may eventually identify genetic factors relevant to thyroid and other cancer risks in horses.

Commonly co-occurring conditions with thyroid tumors include other endocrine disorders affecting senior horses and secondary effects of tumor growth or thyroid dysfunction. Pituitary pars intermedia dysfunction, also known as equine Cushing's disease, occurs commonly in older horses and may be diagnosed concurrently with thyroid tumors. Equine metabolic syndrome may coexist in horses predisposed to metabolic dysfunction. Secondary respiratory complications may develop from tracheal compression. Esophageal dysfunction may accompany large tumors affecting swallowing. Parathyroid abnormalities may occur with thyroid pathology given the close anatomical relationship. Horses with one type of neoplasia may have increased susceptibility to other tumor types.

Conditions with similar symptoms requiring differentiation from thyroid tumors include various causes of cervical swelling and thyroid enlargement. Thyroid hyperplasia, benign enlargement without neoplasia, can mimic tumor clinically. Thyroid cysts, fluid-filled non-neoplastic structures, cause localized thyroid enlargement. Cervical abscesses from Streptococcus equi or other infections create masses in the neck region. Salivary gland disease including mucoceles or tumors occurs in adjacent cervical areas. Lymph node enlargement from infection, inflammation, or lymphoma may present as cervical masses. Laryngeal or paratracheal masses require distinction from thyroid origin. Appropriate diagnostic testing enables accurate differentiation.

Potential complications of thyroid tumors include local effects of growth and consequences of thyroid dysfunction. Tracheal compression from enlarging tumors may cause progressive respiratory compromise, potentially reaching life-threatening severity. Esophageal compression can lead to swallowing difficulty and potential aspiration pneumonia. Invasion of adjacent structures by carcinomas damages cervical tissues and blood vessels. Metastatic spread of carcinomas affects regional lymph nodes and distant organs including lungs. Hyperthyroidism from functional tumors causes metabolic complications including cardiac effects. Post-surgical complications may include hypoparathyroidism, recurrent laryngeal nerve damage, or tumor recurrence. Hemorrhage into tumors may cause acute enlargement and respiratory crisis.