Liver & intrahepatic bile ducts

Benign / nonneoplastic

Mesenchymal hamartoma

Topic Completed: 1 February 2012

Minor changes: 11 June 2021

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Cite this page: Jain D. Mesenchymal hamartoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/livertumormesenchymalhamart.html. Accessed December 8th, 2021.

Definition / general

Well circumscribed, solitary myxoid mass with fluid filled cysts, with architecturally abnormal bile ducts in primitive myxoid stroma (Arch Pathol Lab Med 2006;130:1567)
Third most common tumor of liver in pediatric age group (after hepatoblastoma and infantile hemangioma)
Formerly called cavernous lymphangioadenomatoid tumor, cystic hamartoma, benign mesenchymoma

Clinical features

8% of pediatric liver tumors
75% < age 1 year; rarely adults; 60 - 70% male
Right lobe predilection
Usually asymptomatic
Serum AFP usually normal or mildly elevated; occasionally markedly elevated
Either neoplastic or a developmental anomaly in bile duct plate formation, possible hepatic stellate (Ito) cell origin (Pathol Res Pract 2010;206:532)
Rarely associated with undifferentiated embryonal sarcoma (Pediatr Dev Pathol 2001;4:482) - are pathogenetically related (Genes Chromosomes Cancer 2007;46:508)
Adult cases are usually women with abdominal pain, more prominent fibrosis and a lesser myxoid component than childhood cases, usually no extramedullary hematopoiesis (Hum Pathol 2002;33:893)

Case reports

10 month old girl with cytogenetic analysis (Arch Pathol Lab Med 2006;130:1216)
15 month old asymptomatic boy with large hepatic mass (Case of the Week #61)

Treatment

Excision (curative but surgery has high mortality for large masses)
Liver transplantation may be necessary (J Clin Pathol 2006;59:542)

Gross description

Well circumscribed, solitary, 5 - 23 cm, 20% pedunculated, myxoid mass with fluid filled cysts
May be multiloculated
Becomes fibrotic with age
Cysts are variable sized, contain mucoid or pink fluid with adjacent solid, pink white areas
May have satellite nodules; usually no necrosis, hemorrhage or calcification

Gross images

Images hosted on other servers:

Well demarcated tumor with solid grey cut surface, slightly nodular appearance, isolated small hemorrhagic areas

Microscopic (histologic) description

Epithelial and mesenchymal components
Branching bile ducts without atypia in loose, myxoid stroma with myofibroblast-like cells, dilated vessels and lymphatics
May resemble breast fibroadenoma at low power
Also normal appearing hepatocytes with retention of normal cell plate architecture, thick walled veins, variable collagen
Bile ducts may have mesenchymal collars and are often cystically dilated
Usually extramedullary hematopoiesis (90%)
Often pools of fluid; no tumor giant cells
Adult cases have densely hyalinized or fibrotic stroma and only focal myxoid areas

Microscopic (histologic) images

Case #61

Various images

Positive stains

CK7, vimentin, smooth muscle actin, desmin, actin, glypican 3 (Hum Pathol 2012;43:695)

Negative stains

CK20

Electron microscopy description

Myofibroblastic features

Molecular / cytogenetics description

Interstitial deletion near 19q13.4 (Cancer Genet Cytogenet 2004;153:60)

Differential diagnosis

Bile duct adenoma (no hepatocyte islands) or cystadenoma (adults)
Bile duct hamartoma: usually multiple with fibrous background
Embryonal sarcoma: marked cellularity and atypical cells, eosinophilic PASD globules
Infantile hemangioendothelioma: more vascular
Infantile hemangioma: females more common, vascular channels of variable size
Mixed epithelial mesenchymal hepatoblastoma: epithelial component has embryonal and fetal hepatocytes; mesenchymal component has spindle cells, osteoid, cartilage