Eble JN, Sauter G., Epstein JI, Sesterhenn IA - iarc

A
B
Fig. 1.96 Angiomyolipoma. A Microscopic angiomyolipoma composed of smooth muscle with a minority of fat cells, arising in the renal interstitium. B Rarely,
angiomyolipoma may closely resemble renal oncocytoma.
nents or with prominent cystic change
may be difficult to distinguish from an
epithelial neoplasm preoperatively
{2388}. In some of these cases the diagnosis
is possible by fine-needle aspiration,
supplemented if necessary by
immunohistochemistry {275}.
Macroscopy
AMLs usually are well demarcated from
the adjacent kidney, but not encapsulated.
The colour varies from yellow to pinktan,
depending on the relative proportions
of the various tissue components.
Tumours composed of all three components
may mimic a clear cell RCC whereas
a smooth muscle predominant AML
may mimic a leiomyoma. Although AMLs
may grow to great size, they bulge into
rather than infiltrate the perirenal fat.
Most AMLs are solitary, but multiple
tumours may be present; in such situations,
a large dominant tumour associated
with smaller lesions is typical.
Tumour spread and staging
Infrequently, AML extends into the
intrarenal venous system, the renal vein
or the vena cava. Vascular invasion and
multifocality have occasionally been misinterpreted
as evidence of malignancy
and metastasis. Regional lymph node
involvement can occur; it is considered to
represent a multifocal growth pattern rather
than metastasis {18,2570}.
Only three cases of sarcoma developing in
sporadic AML have been reported; two
patients had pulmonary metastases and one
had hepatic metastases {466,757,1636}.
Histopathology
Most AMLs are composed of a variable
mixture of mature fat, thick-walled poorly
organized blood vessels and smooth
muscle (classic triphasic histology). The
border between AML and the kidney is
typically sharp, although renal tubules
may be entrapped at the periphery of
some tumours. The smooth muscle cells
appear to emanate from blood vessel
walls in a radial fashion, and expansile
growth thereafter may be fascicular. The
smooth muscle cells are most frequently
spindle cells but may appear as rounded
epithelioid cells. Rarely, striking degrees
of nuclear atypia (occasionally with mitotic
activity and multinucleation) may be
seen in these cells, raising the possibility
of malignancy. Some AMLs that are often
located subcapsularly and composed
almost entirely of smooth muscle cells
("capsulomas") resemble leiomyomas.
Cells associated with thin-walled,
branching vessels with a pattern similar
to lymphangioleiomyoma is another variation
of the smooth muscle component.
A
The lipomatous component consists typically
of mature adipose tissue but may
contain vacuolated adipocytes suggesting
lipoblasts, thus mimicking a liposarcoma
when there is extensive adipocytic
differentiation. The blood vessels are
thick-walled and lack the normal elastic
content of arteries. AMLs with a prominent
vascular component may mimic a
vascular malformation. Prominent cystic
change may very rarely be present in
AML.
Immunoprofile
AMLs are characterized by a coexpression
of melanocytic markers (HMB45,
HMB50, CD63, tyrosinase, Mart1/Melan
A and microophthalmia transcription factor)
and smooth muscle markers (smooth
muscle actin, muscle-specific actin and
calponin); CD68, neuron-specific enolase,
S-100 protein, estrogen and progesterone
receptors, and desmin may
also be positive, whereas epithelial markers
are always negative {125,762,1254,
1258,1419,2037,2922}. Coexpression of
Fig. 1.97 Angiomyolipoma. A Deposit of angiomyolipoma in a para-aortic lymph node in the drainage basin
of a kidney bearing an angiomyolipoma. B Cytologic specimen from renal angiomyolipoma. Scattered
HMB45 positive cells within cytologic specimen.
B
66 Tumours of the kidney