Solitary renal myofibromatosis: An unusual cause of infantile hypertension

Introduction. Renovascular disease accounts for the vast majority of cases of infantile hypertension with complications resulting from umbilical arter ial catheterization predominating in the neonatal period and fibrodysplasti c lesions of the renal artery predominating outside the neonatal period. We report a previously undescribed cause of renovascular hypertension: solita ry renal myofibromatosis, Case Report. A 9-month-old male infant was transported to the intensive car e unit at Children's Hospital in Denver, Colorado, for evaluation rind trea tment of a dilated cardiomyopathy and severe systemic hypertension. The chi ld was full-term with no perinatal problems. Specifically, the child never required umbilical arterial catheterization. He was well until 6 months of age when his parents noted poor weight gain. At 9 months of age, he was eva luated at the referral hospital for failure to thrive. On examination he wa s noted to have a blood pressure of 170/110 mm Hg, but no other abnormaliti es. A chest radiograph showed cardiomegaly. Laboratory studies demonstrated normal electrolytes, blood urea nitrogen, and creatinine. However, urinaly sis demonstrated 4+ protein without red blood cells. An echocardiogram show ed severe left ventricular dilatation with an ejection fraction of 16%. On admission the child was noted to be cachectic. His vital signs, including b lood pressure, were normal for age. The physical examination wets unremarka ble. Serum electrolytes, blood urea nitrogen, and creatinine were normal. E chocardiographic studies suggested a dilated hypertrophic cardiomyopathy. H e was started on digoxin and captopril. Subsequently, he demonstrated episo dic hypertension ranging from 170/90 to 220/130 mm Hg. A repeat echocardiog ram 24 hours after admission demonstrated a purely hypertrophic cardiomyopa thy. Verapamil and nifedipine were added to the treatment regimen in an eff ort to better control the blood pressure without success. Urine and blood f or catecholamines and plasma renin activity, respectively, were sent and tr eatment with phentolamine instituted because of a possible pheochromocytoma , A spiral abdominal computerized tomographic scan revealed a markedly abno rmal right kidney with linear streaky areas of calcification around the hil um and also an area of nonenhancement in the posterior upper pole. The adre nals and the left kidney were normal. Doppler ultrasound revealed a decreas e in right renal arterial flow. The urinary catecholamines were normal and surgery was scheduled after the blood pressure was brought under control by medical treatment. At surgery, tumorous tissue and thrombosis of the renal artery were found in the right upper pole. A right nephrectomy was perform ed. Pathologic examination of the kidney showed the presence of a diffuse s pindle cell proliferation in the interstitium of the kidney. The angiogenic /angiocentric character of the proliferation was demonstrated in several-la rge renal vessels. The lumen of most vessels was narrowed and some vessels were totally occluded with recanalization and dystrophic calcifications obs erved. Immunostaining of the tumor demonstrated strong desmin and vimentin positivity and minimal actin positivity in the spindle cells. Mitotic activ ity was not noted in the spindle cell process. These pathologic changes wer e consistent with a diagnosis of infantile myofibromatosis (IM). The child' s preoperative plasma renin activity was 50 712 ng/dL/h (reference range, 2 33-3700 ng/dL/h). Discussion. The causes of systemic hypertension in infancy are many althoug h renal causes are by far the most common. Renal arterial stenosis or throm bosis accounts for 10% to 24% of cases of infantile hypertension. Renal art ery thrombosis is usually a consequence of umbilical arterial catheterizati on, which can also lead to embolization of the renal artery. Renal artery s tenosis may result from fibrodysplastic lesions (74%), abdominal aortitis ( 9%), a complication of renal transplantation (5%), and renal hypoplasia (3% ). IM of the solitary type has never been reported as a cause of systemic h ypertension. In our patient the IM caused both fibrodysplastic lesions and thrombosis of the renal artery, which led to severe systemic hypertension. IM is one of the myofibroblastic diseases of infancy and has three clinicop athologic expressions-solitary, multifocal, and generalized. The solitary a nd multifocal forms are usually limited to the skin, soft tissues, and bone . There is little morbidity and virtually no mortality in these forms of th e disease. The generalized form, in addition to skin and bone involvement, may involve multiple visceral organs including the lungs, kidney, heart, li ver, adrenals, thyroid, and the gastrointestinal tract, This form of the di sease is the least common, usually presents in the first 6 months of life, and is associated with a high morbidity and mortality with death occurring as a result of lung involvement and respiratory failure. To our knowledge, solitary involvement of a viscera without involvement of skin, soft tissues , bone, or other visceral organs has never been reported. All three forms o f IM share a distinctive microscopic appearance of interlacing fascicles of spindle cells. These interlacing fascicles sometimes blend into compact bu ndles with a fibrohyalin stroma in the same tumor. Origination around the b lood vessels, or angiocentricity, is usually present in all types of lesion s. The blood vessels involved in these lesions show intimal hyperplasia lea ding to obliteration of the blood vessels. From these findings it has been postulated that IM is the result of a multifocal proliferation of mesenchym al or myofibroblast-like cells in the walls of blood vessels. These cells s hare morphologic and immunohistochemical characteristics of both fibroblast s and undifferentiated smooth muscle cells. There is usually no evidence of malignant characteristics in these cells. The solitary rind multiple forms of these tumors usually undergo spontaneous regression. In this child we w ere unable to demonstrate evidence of multifocal myofibroblastic lesions. H e seemed to have had a solitary myofibroblastic lesion in the right kidney which led to renal artery stenosis and thrombosis. This produced the renin- related hypertension, which responded only to tumor removal by nephrectomy. He is now growing and developing normally and his cardiomyopathy has resol ved. He is presently normotensive and taking no medications. To date he has had no new or recurrent myofibroblastic lesions. Conclusion. This case demonstrates that IM can present with solitary viscer al organ involvement. The absence of involvement of soft tissues, skin, or bone makes clinical diagnosis of IM nearly impossible when a single viscera is involved in isolation. A biopsy will be needed to make a diagnosis, and surgery may be needed depending on the organ of involvement and the clinic al consequences.