low nephron mass肾下极的肿块？

FSGS, primary or secondary: Primary FSGS denotes an idiopathic cause that typically manifests with heavy proteinuria and nephrotic syndrome and requires immunosuppressive therapy. FSGS is more prevalent in persons of African ancestry. Secondary FSGS is caused by a known etiology, including heroin use, sickle cell disease, scarring of any kind from prior injury, obesity, low nephron mass, HIV, etc. Most cases of secondary FSGS are associated with lower levels of proteinuria (often subnephrotic), higher albumin levels, and less significant edema (e.g., HIV-associated nephropathy is an important exception in that it is associated with heavy proteinuria and rapid progression when untreated). Distinguishing between primary and secondary FSGS is important for therapy (see following text). It should be noted that prior kidney injury can produce morphological features of FSGS over time. Essentially, proteinuric disease attributable to secondary FSGS can be seen in any progressive kidney disease and generally portends worse outcomes.

a) FSGS：可分为原发性或继发性；原发性FSGS表示一种特发的未知原因，通常表现为大量蛋白尿和肾病综合征，需要免疫抑制治疗。FSGS非洲血统的人中更普遍。继发性FSGS是由一种已知的病因引起的，包括海洛因使用、镰状细胞病、既往损伤造成的肾脏疤痕、肥胖、肾下极的肿块、艾滋病毒感染等。大多数继发性FSGS病例表现为较低水平的蛋白尿(通常为亚肾病性)、较高的白蛋白水平和隐匿性水肿(但艾滋病毒相关性肾病是一个重要的特例，因为它表现为大量蛋白尿，且在未经治疗时病情进展迅速)。区分原发性和继发性FSGS对治疗很重要(见下文)。应该注意的是，随着时间的推移，既往的肾脏损伤可产生FSGS的形态学特征。本质上，继发性FSGS引起的蛋白尿疾病可以在任何进展型肾病中看到，且通常预后较差。

low nephron mass肾下极的肿块？谢谢