hyperparathyroidism due to parathyroid abnormalities are classified into three forms : primary , secondary , and tertiary . parathyroid adenoma accounts for about 85% of all cases of hyperparathyroidism , considering all the forms : primary , secondary and tertiary . other less prevalent causes include parathyroid hyperplasia ( 15% ) and carcinoma ( 3 - 4% ) . however , acute primary hyperparathyroidism , or parathyroid crisis ( pc ) , is rare . parathyroid crisis is characterized by life - threatening hypercalcemia of a sudden onset in subjects with phpt . we describe a patient with pc secondary to a giant intrathyroidal parathyroid adenoma who presented with progressive neurological symptoms , nausea and vomiting without medical response to treatment . a 19-year - old female patient was admitted to the orthopedics department for supra - acetabular fibrous dysplasia treatment . after orthopedic surgery , during the second postoperative day she began to suffer from lethargy , nausea , vomiting , and abdominal pain . also , the patient reported muscle weakness , fatigue and a worsening of depressive symptoms . a blood analysis was performed which showed elevated ca ( 14.2 mg / dl , normal laboratory level 8.8 - 10.2 mg / dl ) . the serum phosphorus was low ( 3.99 ng / ml , normal laboratory level 4.0 - 19.0 ng / ml ) with an increased alkaline phosphatase level ( 171 ui / l , normal laboratory level 20 - 90 endocrine evaluation showed elevated parathyroid hormone ( pth ) ( 1207.0 pg / dl , normal laboratory 7 - 82 pg / dl ) . an urgent ultrasonography was requested and showed a 47  22 mm nodule in the left thyroid lobe . after two days of intensive medical treatment , the ca levels had not decreased and the clinical situation of the patient remained similar or even worse . because of life - threatening hypercalcaemia and a poor response to medical treatment , she directly underwent surgery after a consensus decision between the endocrinologists and the surgeons . a hemithyroidectomy was performed assuming it was an intrathyroiidal adenoma and without time for performing a fine needle aspiration because of the patient 's situation . during the surgical procedure , a superior parathyroid gland was observed and not resected . at the end of the hemithyroidectomy , the specimen was open and a clear intra - thyroidal adenoma surrounded by thyroid tissue was observed [ figure 1 ] . unfortunately , intraoperative pth and anathomopathological analyse were avaible but were not used according to the intraoperative findings . on the final anatomopathological examination , it had a maximum diameter of 3 cm and the whole specimen weighted 70 g. the postoperative course was uneventful . the patient received doses of calcium iv during the first day and oral intake began at day two . oral calcium was then given to the patient in the postoperative period until the fist visit at the outpatient clinic . during follow - up , the risk of developing this disease increases with a peak incidence between 50 and 60 years , whereas phpt in children and adolescents is a rare condition . parathyroid crisis is characterized by life - threatening hypercalcemia of sudden onset in subjects with phpt . it has been reported that changes in mental status are characteristic features of hypercalcemic crisis . moreover , she had muscle weakness . although neuromuscular manifestations have been described previously , the pathophysiology of these manifestations is not yet clear . moreover , in pc , as a potentially lethal condition , emergent parathyroidectomy has been advocated . certainly , it has been emphasized that expeditive parathyroidectomy is the cornerstone treatment of patients with pc . there is no clear relationship between surgery and the beginning of toxic , urgent hypercalcaemia . in surgical series there is an estimated reported prevalence of intrathyroidal parathyroid adenoma that varies from 1.4 - 6% . according to embryology , parathyroid glands originate from the third and fourth branchial pouches . after this , the glands caudally migrate to their final positions . any problems during this migration can lead to the glands settling in an anomalous location , even in the thyroid tissue . in a recent study , localization of most of the adenomas ( 70.6% ) was shown to be on the right side and on the lower third of the thyroid lobes . this study also reported that intrathyroidal parathyroid adenomas were present in 3% of patients submitted for parathyroidectomy . however , reports of a giant intrathyroidal parathyroid adenoma in the literature are exceptional . it has been noted that the weight of the adenoma correlates with the severity of the pc . gasparri et al . , found that in a patient with a serum calcium level higher than 15 mg / dl , the mean weight of the removed glands was 4.9 g , whereas it was 2.1 g in patients with serum calcium levels lower than 15 mg / dl . nevertheless , giant parathyroid adenomas are rare . , reported that adenomas heavier than 3.5 g accounted for 7.2% of their series of phpt . differential diagnoses , when very high levels of pth are present , must be established with parathyroid carcinoma . parathyroid carcinoma is a rare malignancy with an incidence rate of less than 1% in all patients surgically treated for primary hyperparathyroidism . to the best of our knowledge the clinical manifestations of hyperparathyroidism in parathyroid carcinoma are usually more severe than in patients with parathyroid adenoma . parathyroid crisis is an emergency because high levels of calcium pose a life - threatening situation for patients . . however , changes in mental status are prevalent , hence , the serum calcium level must be determined in any patient with unexplained central nervous dysfunction . once the patient with pc has been stabilized , expedited parathyroidectomy must be performed .