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Tufted Angioma And Kaposiform Haemangioendothelioma

Kaposiform haemangioendothelioma (KHE) is a rare, often deep-seated, vascular neoplasm usually presenting in children, characterized by lobular infiltrates of capillaries and spindled endothelial cells associated with lymphatic vessels. Tufted angioma (TA), a more superficial lesion, is otherwise essentially identical to KHE. Together, KHE and TA are responsible for virtually all instances of the platelet-trapping syndrome Kasabach–Merritt phenomenon (KMP).

Symptoms & Causes

Introduction

Tufted angioma (TA) and kaposiform haemangioendothelioma (KHE) are vascular tumors in children, with TA being superficial and KHE deeper, both implicated in platelet-trapping syndrome Kasabach–Merritt phenomenon (KMP).

Reference
WHO Classification of Tumours Editorial Board. Soft tissue and bone tumours [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [cited 2024 09 11]. (WHO classification of tumours series, 5th ed.; vol. 3). Available from: https://tumourclassification.iarc.who.int/chapters/33.

Related Terminology
Not recommended: Kaposi-like infantile haemangioendothelioma; haemangioma with Kaposi-like features; angioblastoma of Nakagawa.

Subtype(s)
None

Symptoms

Cutaneous forms are violaceous, infiltrative patches/plaques that may develop nodularity. Deeper soft tissue lesions are bulging indurated masses. Congenital/early infantile cases, especially when large, commonly present with profound thrombocytopenia (KMP). MRI shows an ill-defined, diffusely enhancing T2-hyperintense mass involving multiple tissue layers.

Localization

TA and KHE most commonly affect the skin and deep soft tissues of the extremities, head and neck, trunk, and retroperitoneum; less commonly, the mediastinum, spleen, bone, and testis are affected.

Epidemiology

Most cases present in children aged < 5 years; some are congenital. Congenital/early infantile tumors cause most KMP cases. Rare cases present in older children and adults, without KMP. There is no sex or racial predilection.

Etiology

Unknown

Diagnosis & Treatment

Staging

Not clinically relevant

Pathogenesis

Somatic activating GNA14 mutations have been reported in 2 cases. KMP can be attributed to histologically observed platelet-trapping within tumoral vascular beds, because podoplanin is the natural ligand of CLEC2, a platelet-bound receptor. Platelet transfusions may worsen KMP by stimulating vascular proliferation through intratumoral platelet activation. A self-sustaining cycle of platelet-trapping and tumor growth may drive tumor progression and KMP development.

Macroscopic Appearance

Macroscopically, TA and KHE appear as multiple grey to red infiltrative nodules, encased in fibrous tissue.

Histopathology

Classic KHEs are composed of ill-defined, coalescing nodules of spindled endothelial cells forming elongated slit-like lumina containing erythrocytes, curving around epithelioid nodules enriched in pericytes surrounding platelet-rich microthrombi. Mitoses are infrequent. Variably prominent areas show more typical capillary formation. Dilated crescentic lymphatic vessels surround and intermingle with nodules, most prominently at peripheral margins. Peripheral fibrosis is common around endothelial cell nodules. Perineural invasion may be present. Residua after medical treatment or spontaneous regression are sclerotic versions of the original. Spindled endothelial cells of KHE are positive for CD31, CD34, and ERG, as well as strongly positive for the lymphatic markers podoplanin, LYVE1, and PROX1. TAs are less extensively positive for lymphatic markers, seemingly correlated with reduced endothelial spindling. Expression of the infantile haemangioma–associated marker GLUT1 is absent in KHE/TA. CD31/CD61 immunostaining highlights platelet-rich microthrombi.

Cytology

Not clinically relevant

Prognosis and Prediction

Untreated lesions may partially undergo fibrosis and regress, but they invariably recur. Large lesions are associated with high mortality due to thrombocytopenia or tumor infiltration. Wide local excision, when feasible, can be curative. Medical therapies (e.g., vincristine and steroids) are the first line for high-risk patients with KMP; mTOR inhibition (e.g., sirolimus) is also promising. No distant metastases have been reported; lymph node involvement is rarely seen. This may represent multifocal lymphatic chain involvement rather than true metastasis.

Clinical Features

Diagnostic Molecular Pathology

Not clinically relevant

Essential and Desirable Diagnostic Criteria

Essential: superficial dermal lesions (TA pattern): discrete lobules of capillaries in cannonball pattern within dermal collagen; deeper lesions (KHE pattern): ill-defined, coalescing nodules composed of fascicles of plump spindled endothelial cells that form slit-like lumina that contain erythrocytes – a prominent component of dilated lymphatic vessels is seen at the periphery and in surrounding fibrotic stroma; the spindled cells are positive for CD31, ERG, CD34, and lymphatic markers (podoplanin, LYVE1, PROX1).

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