Pathologic Quiz Case
A 44-Year-Old Woman With an Incidental Asymptomatic Renal Mass
Khaldoon Aljerian, MD; Andrew J. Evans, MD, PhD, FRCPC
A 44-year-old woman underwent an ultrasound exami-
nation for biliary colic that revealed gallstones and
an incidental 3-cm solid mass in the left kidney. She sub-
walled blood vessels. No fat was identiﬁed within the tu-
mor. The mass was nonencapsulated and generally well
demarcated from the adjacent renal parenchyma (Figure
sequently had computed tomographic and magnetic res- 1). Only focally did it form an inﬁltrative border, as evi-
onance imaging scans that conﬁrmed the presence of a 3- denced by areas with entrapped renal tubules and glo-
cm mass located centrally in the midportion of the left meruli. The epithelioid cells had abundant clear to lightly
kidney. The radiologic differential diagnosis was that of eosinophilic granular cytoplasm, large pleomorphic vesic-
renal cell carcinoma versus oncocytoma. Owing to its cen- ular nuclei, and prominent eosinophilic nucleoli (Figure
tral location and proximity to the major renal vessels, the 2). Histochemical staining for periodic acid–Schiff/peri-
mass was resected laparoscopically by complete nephrec- odic acid-Schiff–diastase demonstrated the presence of cy-
tomy. toplasmic glycogen. A particularly striking feature was the
The specimen consisted of a kidney covered by peri- presence of numerous huge cells with straplike morphol-
nephric fat, measuring 9.6 6.0 6.4 cm, and a segment ogy, eosinophilic cytoplasm, and multiple peripherally
of ureter measuring 4.5 0.4 cm. The renal capsule was distributed nuclei (Figures 1 and 3). These nuclei were
intact and smooth. On bivalving the kidney coronally, markedly pleomorphic and had coarse chromatin and
there was a 2.5 2.5 2.3-cm, solid, circumscribed, large eosinophilic nucleoli. The straplike cells were typi-
brownish-red mass located in the midportion of the kid-
cally concentrated around blood vessels and were fre-
ney adjacent to, but not extending into, the renal pelvis.
quently associated with an admixture of lymphocytes.
Necrosis and hemorrhage were not grossly apparent, and
There were rare foci of necrosis. Mitotic activity was not
the renal vein was grossly uninvolved. The remaining re-
identiﬁed. There was no invasion of the renal capsule or
nal parenchyma was grossly unremarkable.
Sections from the mass showed a highly cellular neo- extrarenal soft tissue. Lymphovascular invasion was not
plasm comprising predominantly epithelioid cells with fo- identiﬁed, and the resection margins were free of tumor.
cal spindle cell morphology and scattered, large, thick- Immunohistochemically, the tumor cells were strongly
positive for HMB-45 (Figure 4) and Melan-A (MART-1)
and were focally positive for CD68. The spindle cell ele-
Accepted for publication April 23, 2004. ment stained positively for smooth muscle actin. Staining
From the Department of Pathology and Laboratory Medicine, Univer-
sity Health Network, Princess Margaret Hospital, Toronto, Ontario.
for cytokeratins AE1/AE3, CAM 5.2, 34 E12, 7, and 20
The authors have no relevant ﬁnancial interest in the products or was negative. The tumor cells also showed negative stain-
companies described in this article. ing with renal cell carcinoma (RCC), CD10, epithelial
Corresponding author: Andrew J. Evans, MD, PhD, FRCPC, Depart- membrane antigen, vimentin, desmin, sarcomeric actin,
ment of Pathology and Laboratory Medicine, University Health Net- muscle-speciﬁc actin, CD45, and S100.
work, Princess Margaret Hospital, 610 University Ave, Room 4-313,
Toronto, Ontario, Canada M5G 2M9 (e-mail: firstname.lastname@example.org. The patient is currently well and shows no evidence of
ca). recurrent disease after 8 months of follow-up.
Reprints not available from the authors. What is your diagnosis?
1176 Arch Pathol Lab Med—Vol 128, October 2004 Pathologic Quiz Case—Aljerian & Evans
Arch Pathol Lab Med—Vol 128, October 2004 Pathologic Quiz Case—Aljerian & Evans 1177
Pathologic Diagnosis: Atypical Epithelioid epithelioid AML reported by Pea et al8 were associated
Angiomyolipoma with metastases and death within 12 to 18 months of di-
Angiomyolipomas (AMLs) are benign kidney tumors agnosis. In contrast, each of the patients with atypical
that typically consist of thick-walled blood vessels, smooth AMLs in the series of Delgado et al7 had no evidence of
muscle, and mature fat admixed in variable proportions. recurrent disease during follow-up that ranged from 1 to
Angiomyolipoma was initially described in 1942 as a 8 years. The cases described by Pea et al8 and Delgado et
hamartomatous lesion associated with the tuberous scle- al7 shared essentially the same histomorphologic features,
rosis complex (TSC).1 Current evidence demonstrating including epithelioid and bizarre, large, multinucleated
clonality has revealed that AMLs are truly neoplastic in cells. From the aforementioned reports, it would appear
nature.2 Approximately one half of AMLs occur in asso- that no deﬁnitive statement can be made with respect to
ciation with TSC, while the other half are sporadic. A de- predicting malignant behavior based on features such as
ﬁning feature of AML is the characteristic positive im- inﬁltrative tumor borders, vascular invasion, atypia, mi-
munoreactivity of the smooth muscle cells for both muscle totic activity, or even local recurrence after incomplete re-
markers and the melanoma-associated antigen HMB-45.3 section. It is also tempting to speculate that in the setting
It is now apparent that AMLs contain a fourth cell type of TSC, metastatic AML may not represent true metasta-
that is considered to be their putative cell of origin. This ses, but rather new primary tumors arising from perivas-
fourth cell type is a vascular smooth muscle cell, or peri- cular epithelioid cells in other organs in a predisposed
cyte capable of divergent differentiation, now commonly patient. It is clear that there is a need for more of these
referred to as the ‘‘perivascular epithelioid cell.’’ In fact, cases to be reported in order to determine the optimal
it has been suggested that perivascular epithelioid cells treatment and follow-up strategy for a given patient.
give rise to a spectrum of lesions, which includes renal As described by Delgado et al,7 the differential diag-
and extrarenal AML, clear cell ‘‘sugar’’ tumors of the lung nosis of atypical/epithelioid AML includes RCC of clear
and pancreas, and lymphangioleiomyomatosis.4,5 All of cell type, sarcomatoid RCC, adrenocortical carcinoma, pri-
these lesions have the common feature of myomelanocytic mary pleomorphic renal sarcoma, and even metastatic
differentiation, suggestive of a common neural crest ori- melanoma. Recognition of the characteristic bizarre strap-
gin. like cells and their distribution with respect to blood ves-
In rare instances, AMLs have unusual morphologic fea- sels in the tumor, along with an immunohistochemical
tures, such as a predominance of epithelioid cells, the ab- panel that includes cytokeratins, muscle markers, HMB-
sence of recognizable fat, and striking cytologic atypia that 45, and S100, should allow the correct diagnosis to be
is usually not accompanied by mitotic activity. These le- made.
sions have been designated epithelioid AMLs6 and atypi- References
cal AMLs.7 These unusual AML variants can give rise to 1. Moolten SE. Hamartial nature of the tuberous sclerosis complex and its
diagnostic confusion with RCC, renal sarcomas, or metas- bearing on the tumor problem: report of a case with tumor anomaly of the kidney
tases involving the kidney. Delgado et al7 reported 5 ex- and adenoma sebaceous. Arch Intern Med. 1942;69:589–623.
2. Green AJ, Sepp T, Yates JR. Clonality of tuberous sclerosis hamartomas
amples of atypical AML with essentially the same histo- shown by non-random X-linked chromosome inactivation. Hum Genet. 1996;97:
morphologic features as the ones we found in this patho- 240–243.
logic quiz case, namely, the presence of bizarre multinu- 3. Sturtz CL, Dabbs DJ. Angiomyolipomas: the nature and expression of the
HMB-45 antigen. Mod Pathol. 1994;7:842–845.
cleated straplike cells with an absence of mitotic activity. 4. Bonetti F, Pea M, Martignoni G, et al. Clear cell (‘‘sugar’’) tumor of the lung
Four of the 5 cases described by Delgado et al7 were spo- is a lesion strictly related to angiomyolipoma: the concept of a family of lesions
radic lesions, as was our case, while 1 was associated with characterized by the presence of perivascular epithelioid cells (PEC). Pathology.
TSC. 5. Zamboni G, Pea M, Martignoni G, et al. Clear cell ‘‘sugar’’ tumor of the
To illustrate the diagnostic confusion that can be created pancreas: a novel member of the family of lesions characterized by the presence
by atypical AML variants, Pea et al8 reviewed a series of of perivascular epithelioid cells. Am J Surg Pathol. 1996;20:722–730.
5 tumors in TSC cases that were originally classiﬁed as 6. Mai T, Perkins DG, Collins JP. Epithelioid cell variant of renal angiomyoli-
poma. Histopathology. 1996;28:277–280.
RCCs. Three of the 5 tumors were reclassiﬁed as epithe- 7. Delgado R, de Leon Bojorge B, Albores-Saavedra J. Atypical angiomyoli-
lioid AMLs based on positive immunohistochemical stain- poma of the kidney: a distinct morphologic variant that is easily confused with
ing with HMB-45 and negative staining for cytokeratin. a variety of malignant neoplasms. Cancer. 1998;83:1581–1592.
8. Pea M, Bonetti F, Martignoni G, et al. Apparent renal cell carcinomas in
Most of these atypical AML variants appear to behave tuberous sclerosis are heterogeneous: the identiﬁcation of malignant epithelioid
in a benign manner; however, some will follow a more angiomyolipoma. Am J Surg Pathol. 1998;22:180–187.
aggressive course. There are isolated case reports of oth- 9. Cibas ES, Goss GA, Kulke MH, et al. Malignant epithelioid angiomyolipoma
erwise typical AMLs having areas of malignant transfor- (‘‘sarcoma ex angiomyolipoma’’) of the kidney: a case report and review of the
literature. Am J Surg Pathol. 2001;25:121–126.
mation,9,10 which in 1 case was referred to as ‘‘sarcoma ex 10. Kawaguchi K, Oda Y, Nakanishi K, et al. Malignant transformation of renal
angiomyolipoma.’’ 9 In addition, 2 of the 3 examples of angiomyolipoma: a case report. Am J Surg Pathol. 2002;26:523–529.
1178 Arch Pathol Lab Med—Vol 128, October 2004 Pathologic Quiz Case—Aljerian & Evans