Elliot K. Fishman M.D.
Johns Hopkins Hospital

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“The perirenal space is a retroperitoneal space that is limited anteriorly by the anterior renal fascia (Gerota fascia) and posteriorly by the posterior renal fascia (Zuckerkandl fascia).These two fasciae fuse to form the lateroconal fascia laterally and blend loosely with the periureteric connective tissue medially. Superiorly, the two fasciae are fixed to the diaphragmatic fascia above the adrenal glands; inferiorly, they blend with the iliac fascia.The anterior and posterior renal fasciae enclose a gradually tapering conelike space produced by the embryologic ascent of the kidneys from the pelvis to the adult retroperitoneal position.”
Neoplastic and Non- neoplastic Proliferative Disorders of the Peri-renal Space: Cross- sectional Imaging Findings 
Surabhi VR et al.
RadioGraphics 2008; 28:1005–1017

Neoplastic and Non- neoplastic Proliferative Disorders of the Peri-renal Space: Cross- sectional Imaging Findings 
Surabhi VR et al.
RadioGraphics 2008; 28:1005–1017

Neoplastic and Non- neoplastic Proliferative Disorders of the Peri-renal Space: Cross- sectional Imaging Findings 
Surabhi VR et al.
RadioGraphics 2008; 28:1005–1017

“Erdheim-Chester disease is a non–Langerhans cell histiocytosis characterized by the infiltration of foamy histiocytes with fibrosis that can affect many organs, most commonly long bones. Renal involvement commonly manifests in this disease as a histiocytic infiltration into the perirenal fat. Histopathologic findings from biopsy of the right retroperitoneal region included fragments of fibroadipose tissue displaying a lymphohistiocytic infiltrate.” 
The Hairy Kidney of Erdheim-Chester Disease
Scolaro JC, Peiris AN
Mayo Clin Proceed May 2018Volume 93, Issue 5, Page 671

“Erdheim-Chester disease is a non–Langerhans cell histiocytosis characterized by the infiltration of foamy histiocytes with fibrosis that can affect many organs, most commonly long bones. Renal involvement commonly manifests in this disease as a histiocytic infiltration into the perirenal fat. Histopathologic findings from biopsy of the right retroperitoneal region included fragments of fibroadipose tissue displaying a lymphohistiocytic infiltrate.” 
The Hairy Kidney of Erdheim-Chester Disease
Scolaro JC, Peiris AN
Mayo Clin Proceed May 2018Volume 93, Issue 5, Page 671

“Erdheim–Chester disease (ECD) is first described by Jacob Erdheim and William Chester in 1930 and is also referred to as lipogranulomatosis. ECD is a systemic inflammatory disorder with a poor prognosis. Skeletal system is the most commonly involved body part, however, around 50% of the cases may have extraskeletal involvement. Symmetrical diaphyseal and metaphyseal osteosclerosis of the long bones is the typical skeletal finding. Among the extraskeletal sites that are involved central nervous system, pulmonary and cardiovascular systems, orbital cavity and cutaneous system may be counted in addition to the kidneys and the retroperitoneum.”
Computed tomography and magnetic resonance imaging of peripelvic and periureteric pathologies.
Gumeler E et al. 
Abdom Radiol (NY). 2018 Sep;43(9):2400-2411

“For genitourinary system evaluation in patients with ECD, CT may be utilized as the first modality of choice. The so called “hairy kidney appearance,” due to perirenal involvement, is typically characterized by hypoattenuating, irregularly shaped soft tissue masses with minimal enhancement after contrast injection. This finding is very frequent in cases with renal ECD, with a reported rate of 68% of all patients with genitourinary involvement. Infiltrative extension towards the kidney periphery into the renal sinus may be observed.”
Computed tomography and magnetic resonance imaging of peripelvic and periureteric pathologies.
Gumeler E et al. 
Abdom Radiol (NY). 2018 Sep;43(9):2400-2411

”Retroperitoneal involvement with ECD can manifest as a mass-like infiltrative surrounding the abdominal aorta with the same characteristics of the perirenal lesions. This can lead to acute or slowly progressive renal insufficiency. Retroperitoneal involvement frequently includes a bilateral, symmetric, and diffuse thickening of the adrenal glands associated with infiltration of the adjacent fat.”
Spectrum of abdominal imaging findings in histiocytic disorders. 
de Souza Maciel Rocha Horvat, N., Coelho, C.R., Roza, L.C. et al. 
Abdom Imaging 40, 2738–2746 (2015). https://doi.org/10.1007/s00261-015-0449-1

“In summary, urinary involvement in ECD was mostly bilateral and symmetric. Early identification of the perirenal hairy kidney sign is critical for accurate diagnosis and timely treatment. Understanding of the CT findings and progression as well as correct diagnosis based on radiological findings, have significant implications for guiding ECD treatment.” 
Urinary involvement in Erdheim–Chester disease: computed tomography imaging findings 
Zhe Wu et al.
Abdominal Radiology (2021) 46:4324–4331