Case 35
Diagnosis and discussion
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- Multicystic renal dysplasia (congenital)

The biopsy of the retroperitoneal (parahiliar renal) mass (green arrows in Figure 1) reveals clusters of histiocytes with ample granular eosinophilic cytoplasm; this cells are known as "von Hansemann cells". This eponym was coined because is considered that the first human case of malacoplakia was seen by the German professor von Hansemann (1901). Professor von Hanseman then spoke to his assistant Dr Gutmann and provided him with details of his case, as Dr Michaelis, an expert biochemist, had agreed to study the disease further in a collaborative venture. Not knowing how history would be written, von Hansemann published his paper in 1903: von Hansemann D. Über Malakoplakie der Harnblase. Virch Arch Path Anat 1903; 173: 302–8, a year after Michaelis and Gutmann described the first human case: Michaelis L, Gutmann C. Ueber Einschlüsse in Blasentumoren. Ztschr Klin Med 1902; 47: 208–15. (Dasgupta P, Womack C, Turner AG, Blackford HN. Malacoplakia: von Hansemann's disease. BJU Int. 1999;84(4):464-9. [PubMed link])

In many of this type of histiocytes there is one or several round basophilic structures measuring between 1µm and 10µm approximately, some are laminated, others appear homogeneous, and others have a dense central core with a targetoid appearance; these are known as "Michaelis-Gutmann bodies".

Nephrectomy of the right kidney demonstrated a main cystic cavity and areas with primitive (fetal) appearance aspect and other small cysts, diagnostic of focal congenital multicystic renal dysplasia (Figures 2 and 3).

Malakoplakia (some authors write "malacoplakia") is a chronic inflammatory process which most often affects the urinary tract, but it may involve a variety of other organs.

The term malakoplakia was coined by von Hansemann in 1903 and is derived from the Greek words malakos (soft) and plakos (plaque).

Malakoplakia is the result of an acquired defect in macrophage function causing impairment of bactericidal activity. The large macrophages that are present at sites of infection (von Hansemann cells) exhibit numerous secondary lysosomes containing partially digested organisms. Fusion and calcification of these lysosomes results in the formation of intracytoplasmic bodies called Michaelis-Gutmann bodies, considered pathognomonic of malakoplakia.

See the chapter Tubulointerstitial diseases of our Tutorial.

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