We describe a 37-year-old patient who presented with right lower quadrant pain and intermenstrual bleeding. MRI demonstrated a 5 ϫ 5 cm lobulated mass centered in the right uterine wall interpreted as suspicious for malignancy. A total hysterectomy was performed, and the gross and histologic features were consistent with the diagnosis of a uterus-like mass. Uterus-like mass is a benign entity that can be found in a variety of organs, and is characterized by endometrium surrounded by smooth muscle. It is an extremely rare lesion with only approximately 15 cases reported in the current literature. There is a lack of imaging literature on this entity, which is primarily described in the pathology literature. Its histogenesis is uncertain, but is theorized to be metaplastic change, congenital anomaly, and/or heterotopia. However, given the MRI appearance in this case, we feel that uterus-like mass could be prospectively diagnosed or listed in a differential diagnosis.

Summary. Parathyroid hormone (PTH) metabo-lism in pregnancy has not been clearly defined. Studies have reported either increased or unchanged values of immunoreactive PTH (iPTH). However, iPTH levels do not necessarily correlate with hormonal bioactivity due to the presence of immunoreactive but nonbioactive PTH fragments. In this study we evaluated PTH metabolism in the third trimester of pregnancy by determining iPTH blood levels as well as the biological effects of PTH, assessed by tubular maximum phosphate reabsorption (TmP) and nephrogenous cAMP (ncAMP) excretion, in 10 young, healthy pregnant patients (mean gestational age 35 weeks) and 10 young, healthy age-matched female controls. Pregnancy was associated with a significant increase in creatinine clearance (146 _+ 13 vs 106 _+ 9 ml/min, P < 0.01), and a significant decrease in total fasting serum calcium (8.4 _+ 0.1 vs 9.0 + 0.1 mg/dl, P < 0.001) and serum albumin (3.6 _+ 0.1 vs 4.2 +_ 0.1 g/dl, P < 0.001). There was no significant difference in iPTH (3.7 + 0.4 vs 4.3 _+ 0.5 /zlEq/ml), serum phosphorus (3.6 +_ 0.1 vs 3.8 __ 0.2 mg/dl), TraP (3.61 _+ 0.13 vs 3.75 + 0.25 mg/100 ml GFR), or ncAMP (1.68 +_ 0.20 vs 1.88 +_ 0.23 nmoles/100 ml GFR) between the two groups. Pregnancy was attended by a significant increase in fasting urinary calcium to creatinine ratio (0.14 +_ 0.03 vs 0.06 _+ 0.01, P < 0.05), an index of bone resorption. The data suggest that the biological effects of PTH are unchanged in pregnancy, and that reported increments in 1,25(OH)2 vitamin D in pregnancy are not regulated by changes in either PTH, calcium, or phosphate. terminal [12] fragments. These differences may reflect the use of different antibodies to PTH. Alternatively, even though serum concentrations of iPTH are normal in pregnant women [11,12], an increased turnover of the hormone is not excluded. Since the carboxy-terminal fragment of PTH is largely removed from the circulation by glomerular filtration [13], and since glomerular filtration increases during pregnancy, iPTH levels as determined by antibodies to the carboxy-terminal fragment may not reflect in vivo hormonal activity. To evaluate the effects of pregnancy on the biological effects of PTH, we have measured nephrogenous cyclic AMP (ncAMP), a sensitive indicator of in vivo PTH activity [14,15], and the tubular maximum phosphate reabsorption (TmP) [16,17] in 10 pregnant and 10 nonpregnant young women and correlated these values with serum levels of iPTH employing an antiserum to the carboxy-terminal fragment. We found that neither iPTH levels, ncAMP, nor TmP was altered during the third 0171-967X/82/0034-0009 $01.00