The brown tumor is a kind of complication of hyperparathyroidism (HPT). The ultimate therapy usually is the resolution of HPT. We herein report an unlocatable HPT patient who received resection of a huge brown tumor of the rib, and experienced “self-recovery” of serum calcium and parathyroid hormone.

A 34-year-old female patient who suffered from a gradually increasing mass of the left chest wall since 2007 came to our hospital for treatment. The patient had a history of serum Ca and parathyroid hormone (PTH) increasing since June 2015 and received zoledronic acid treatment for 17 mo. When she came to our hospital in November 2017 after discontinuing medical treatment for 3 mo, the serum Ca and PTH levels were within normal ranges. The patient had no imaging abnormalities of parathyroid ultrasound or ^99mTc-methoxyisobutyl isonitrile. Enhanced computed tomography revealed a local soft tissue mass of 96 mm × 113 mm with bone erosion of the left 8^th rib, and the mass presented irregular enhancement with an unclear boundary between the mass and spleen. The mass was thought to likely be caused by HPT, but a malignancy could not be ruled out. Resection of the mass was performed, and the pathology proved that the mass was a brown tumor. A diagnosis of unlocatable HPT was considered. Since the serum Ca and PTH levels were both normal pre- and post-operation, the patient did not receive exploratory surgery for HPT, and received regular follow-up.

The huge brown tumor of the rib and “self-recovered” serum PTH and Ca levels are relatively rare in HPT patients. An exploratory operation may be deferred for these patients, and long-term follow-up should be performed.

The brown tumor is a kind of complication of hyperparathyroidism (HPT), and it may sometimes be the initial symptom of HPT. The ultimate therapy is the resolution of HPT. Here, we reported an interesting case of unlocatable HPT that involved a resection of a huge brown tumor of the rib, and experienced “self-recovered” serum parathyroid hormone (PTH) and calcium.

The diagnosis of a brown tumor was considered, but a malignancy could not be ruled out.

The patient was admitted into the General Surgery Department on December 25, 2017. A mass resection was performed. A thoracoabdominal incision was chosen, and the mass was found originating from the 9-10^th ribs. The mass was separated from the compressed tissues, and was excised completely with part of the 9-10^th ribs (Figure 4). Then the diaphragm was repaired and the incision was closed. The pathology was a brown tumor of HPT.

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Figure 4 Gross pathology of the mass originating from the 9-10^th ribs.

The patient did not receive medication after the surgery, and was discharged without complications on the 7^th d after operation. Serum PTH (54.6 pg/mL) and Ca (2.28 mmol/L) were in the normal range on July 9, 2019.

Brown tumors are giant-cell lesions due to primary or secondary HPT, and may occur in about 4.5% of primary HPT patients and 1.5% of secondary HPT patients[1]. The common locations of brown tumors are pelvis, ribs, long bone shaft, clavicle, and jaw[2]. Brown tumors may sometimes be the first manifestation of HPT, and should be differentially diagnosed with solitary bone lesions, such as metabolic osteopathy, multiple myeloma, Langerhans’ cell histiocytosis, leukemia, multiple bone cysts, multiple non-ossifying fibroma, and fibrous dysplasia[2,3]. In our case, although the patient has a temporary increase of serum Ca and PTH, the serum or urinary Ca and serum PTH were normal when she came to our hospital. The results of cervical ultrasound and ^99mTc-MIBI were also negative. Thus, the diagnosis should be made more prudently. The resection of the mass could not only relieve symptoms, but also exclude the possibility of malignancy.

However, the diagnosis of primary HPT may be inerrant when considering the pathology of the bone lesion and past medical history. The patient realized the mass of the left chest wall 10 years ago, but HPT was considered about 8 years later when high levels of serum Ca and PTH were found. She received zoledronic acid treatment for hypercalcemia for a period of time, which was then discontinued. The preoperative laboratory tests revealed normal serum/urinary Ca and PTH, with negative results from imaging examinations. For a suspicious primary HPT, cervical ultrasound and ^99mTc-MIBI are usually used for location, and the sensitivities are 54% and 59%, respectively[2]. However, combined imaging of the two methods could reach a sensitivity of about 90%[2,4]. The main reasons for false-negative ultrasound include abnormal migration of the inferior parathyroid glands (substernal, retrotracheal or retroesophageal)[5], obesity[6], and interference of thyroid lesions[7]. The imaging of ^99mTc-MIBI depends on the percentage of mitochondria-rich oxyphil cells, growth phase of glands, and P-glycoprotein levels[6]. PTH level and gland volume are important factors that influence imaging sensitivity[6,8].

When there are no positive results in all of the imaging examinations except for hypercalcemia, and high levels of PTH occur, surgical exploration may be tried. According to the study of Amin et al[2], hyperfunctioning glands are not more frequently located on a particular side or anatomical position. Therefore, intraoperative parathyroid hormone monitoring can be used to guide the resection. Considering that the serum Ca and PTH levels of our patient are within the normal ranges, the patient did not receive the exploratory surgery. However, she needs long-term follow-up to monitor laboratory tests and dynamic changes of primary lesions. The transient HPT with “self-recovery” of PTH is rare. Kim[9] reported an adult female patient with acute kidney injury (AKI) who experienced a transient elevation of PTH. However, the PTH elevation resolved after several weeks, in parallel with improving renal function, and the patient did not develop a brown tumor during this short time period. Our patient has no history of AKI or CKD, and the formation of the brown tumor suggests that the HPT may have existed for a long time. Thus, unlocatable primary HPT should be considered. There has been evidence that zoledronic acid could reduce the level of PTH in HPT of CKD[10], but a similar efficacy in primary HPT is unclear. Close follow-up should therefore be performed in case of recurrent elevation of PTH in the future.

Although there are some unlocatable HPT reports, cases involving a huge brown tumor of the rib and “self-recovered” serum PTH and Ca are relatively rare. An exploratory operation may be deferred for these patients, and long-term follow-up should be performed.