Kaposiform lymphangiomatosis: Diagnosis, pathogenesis, and treatment.

Kaposiform lymphangiomatosis (KLA) is a life-threatening rare disease that can cause substantial morbidity, mortality, and social burdens for patients and their families. Diagnosis often occurs long after initial symptoms, and there are few centers in the world with the expertise to diagnose and care for patients with the disease. KLA is a lymphatic anomaly and significant advancements have been made in understanding its pathogenesis and etiology since its first description in 2014. This review provides multidisciplinary, comprehensive, and state-of-the-art information on KLA patient presentation, diagnostic imaging, pathology, organ involvement, genetics, and pathogenesis. Finally, we describe current therapeutic approaches, important areas for research, and challenges faced by patients and their families. Further insights into the pathogenesis of KLA may advance our understanding of other vascular anomalies given that similar signaling pathways may be involved.

Endothelial cell expression of mutant Map2k1 causes vascular malformations in mice.

Extracranial arteriovenous malformation (AVM) is a congenital vascular anomaly causing disfigurement, bleeding, ulceration, and pain. Most lesions are associated with somatic MAP2K1 activating mutations in endothelial cells (ECs). The purpose of this study was to determine if EC expression of mutant activated MAP2K1 is sufficient to produce vascular malformations in mice. We generated mice with a ROSA26 allele containing a lox-stop-lox gene trap (GT), Map2k1 cDNA with an activating p.K57N missense mutation, an internal ribosomal entry site, and green fluorescent protein cDNA (R26GT-Map2k1-GFP). We expressed mutant MAP2K1 and GFP in ECs of fetal and newborn mice using Tg-Cdh5Cre or Tg-Cdh5CreER alleles. Tg-Cdh5Cre+/-;R26GT-Map2k1-GFP/+ animals that express mutant MAP2K1 in ECs in utero developed diffuse vascular abnormalities and died by embryonic (E) day 16.5. Tg-Cdh5CreER+/-;R26GT-Map2k1-GFP/+ animals in which mutant MAP2K1 expression was induced in ECs by tamoxifen at postnatal (P) day 1 developed vascular malformations in the brain, ear, and intestines by P23. The lesions consisted of abnormal networks of blood vessels containing recombined and non-recombined ECs. In conclusion, expression of MAP2K1 p.K57N is sufficient to cause vascular malformations in mice. This model can be used to study the malformation process and for pre-clinical pharmacologic studies.

Kaposiform Lymphangiomatosis: Pathologic Aspects in 43 Patients.

Kaposiform lymphangiomatosis is an uncommon generalized lymphatic anomaly with distinctive clinical, radiologic, histopathologic, and molecular findings. Herein, we document the pathology in 43 patients evaluated by the Boston Children's Hospital Vascular Anomalies Center from 1999 to 2020. The most frequent presentations were respiratory difficulty, hemostatic abnormalities, and a soft tissue mass. Imaging commonly revealed involvement of some combination of mediastinal, pulmonary, pleural, and pericardial compartments and most often included spleen and skeleton. Histopathology was characterized by dilated, redundant, and abnormally configured lymphatic channels typically accompanied by dispersed clusters of variably canalized, and often hemosiderotic, spindled lymphatic endothelial cells that were immunopositive for D2-40, PROX1, and CD31. An activating lesional NRAS variant was documented in 9 of 10 patients. The clinical course was typically aggressive, marked by hemorrhage, thrombocytopenia, diminished fibrinogen levels, and a mortality rate of 21%.

Congenital Disseminated Pyogenic Granuloma: Characterization of an Aggressive Multisystemic Disorder.

OBJECTIVE: To describe the clinical, radiologic, and histopathologic features of "congenital disseminated pyogenic granuloma" involving various organs with high morbidity related to cerebral hemorrhagic involvement. STUDY DESIGN: We searched the database of the Vascular Anomalies Center at Boston Children's Hospital from 1999 to 2019 for patients diagnosed as having multiple vascular lesions, visceral vascular tumors, congenital hemangiomatosis, multiple pyogenic granulomas, or multiple vascular lesions without a definite diagnosis. A retrospective review of the medical records, photographs, histopathologic, and imaging studies was performed. Only patients with imaging studies and histopathologic diagnosis of pyogenic granuloma were included. RESULTS: Eight children (5 male, 3 female) had congenital multifocal cutaneous vascular tumors. Lesions also were found in the brain (n = 7), liver (n = 4), spleen (n = 3), muscles (n = 4), bone (n = 3), retroperitoneum (n = 3), and intestine/mesentery (n = 2). Less commonly affected were the spinal cord, lungs, kidneys, pancreas, and adrenal gland (n = 1 each). The mean follow-up period was 21.8 months. The cerebral and visceral lesions were hemorrhagic with severe neurologic sequelae. The histopathologic diagnosis was pyogenic granuloma with prominent areas of hemorrhage and necrosis. The endothelial cells had enlarged nuclei, pale cytoplasm and were immunopositive for CD31 and negative for D2-40 and glucose transporter 1. CONCLUSIONS: Congenital disseminated pyogenic granuloma is a distinct multisystemic aggressive disorder that primarily affects the skin, brain, visceral organs, and musculoskeletal system. Differentiation of this entity from other multiple cutaneous vascular lesions is critical because of possible cerebral hemorrhagic involvement.

Fibroadipose Vascular Anomaly in the Upper Extremity: A Distinct Entity With Characteristic Clinical, Radiological, and Histopathological Findings.

PURPOSE: Fibroadipose vascular anomaly (FAVA) is an intramuscular vascular malformation that has been recently described as a distinct clinical entity. The clinical, radiological, and histopathological characteristics of FAVA in the upper extremity are reviewed. METHODS: This was a retrospective case series of upper-extremity FAVA lesions. RESULTS: We reviewed 19 patients with FAVA of the upper limb. Pain, stiffness, swelling, and flexion contractures were the most common presentations. Except for one lesion confined to the hand, all lesions either presented with or developed a contracture within 10 years. Ten patients underwent surgical debulking. Six required tendon transfer reconstruction and 3 necessitated a free functional muscle transfer. CONCLUSIONS: Fibroadipose vascular anomaly in the upper extremity requires an accurate diagnosis and may benefit from early referral to a multidisciplinary vascular anomaly center with experienced hand surgeons. Compression garments, propranolol, and sclerotherapy seem to be ineffective. Surgical resection focused on symptomatic regions with appropriate reconstruction may have benefit in salvage of limbs with compromised function. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

Intramuscular fast-flow vascular anomaly contains somatic MAP2K1 and KRAS mutations.

BACKGROUND: The term "intramuscular hemangioma capillary type" (IHCT) refers to a fast-flow vascular lesion that is classified as a tumor, although its phenotype overlaps with arteriovenous malformation (AVM). The purpose of this study was to identify somatic mutations in IHCT. METHODS: Affected tissue specimens were obtained during a clinically indicated procedure. The diagnosis of IHCT was based on history, physical examination, imaging and histopathology. Because somatic mutations in cancer-associated genes can cause vascular malformations, we sequenced exons from 446 cancer-related genes in DNA from 7 IHCT specimens. We then performed mutation-specific droplet digital PCR (ddPCR) to independently test for the presence of a somatic mutation found by sequencing and to screen one additional IHCT sample. RESULTS: We detected somatic mutations in 6 of 8 IHCT specimens. Four specimens had a mutation in MAP2K1 (p.Q58_E62del, p.P105_I107delinsL, p.Q56P) and 2 specimens had mutations in KRAS (p.K5E and p.G12D, p.G12D and p.Q22R). Mutant allele frequencies detected by sequencing and confirmed by ddPCR ranged from 2 to 15%. CONCLUSIONS: IHCT lesions are phenotypically similar to AVMs and contain the same somatic MAP2K1 or KRAS mutations, suggesting that IHCT is on the AVM spectrum. We propose calling this lesion "intramuscular fast-flow vascular anomaly."

A somatic activating NRAS variant associated with kaposiform lymphangiomatosis.

PURPOSE: Kaposiform lymphangiomatosis (KLA) is a rare, frequently aggressive, systemic disorder of the lymphatic vasculature, occurring primarily in children. Even with multimodal treatments, KLA has a poor prognosis and high mortality rate secondary to coagulopathy, effusions, and systemic involvement. We hypothesized that, as has recently been found for other vascular anomalies, KLA may be caused by somatic mosaic variants affecting vascular development. METHODS: We performed exome sequencing of tumor samples from five individuals with KLA, along with samples from uninvolved control tissue in three of the five. We used digital polymerase chain reaction (dPCR) to validate the exome findings and to screen KLA samples from six other individuals. RESULTS: We identified a somatic activating NRAS variant (c.182 A>G, p.Q61R) in lesional tissue from 10/11 individuals, at levels ranging from 1% to 28%, that was absent from the tested control tissues. CONCLUSION: The activating NRAS p.Q61R variant is a known "hotspot" variant, frequently identified in several types of human cancer, especially melanoma. KLA, therefore, joins a growing group of vascular malformations and tumors caused by somatic activating variants in the RAS/PI3K/mTOR signaling pathways. This discovery will expand treatment options for these high-risk patients as there is potential for use of targeted RAS pathway inhibitors.

Multimodal treatment approach in a patient with multiple intracranial myxomatous aneurysms.

The most common primary cardiac tumor is myxoma, typically originating in the left atrium. Emboli to the central nervous system can cause cerebral infarction or, rarely, seed tumor growth within vessel walls, causing myxomatous aneurysms. Fewer than 60 myxomatous aneurysms have been reported, including 2 cases in children. Here, the authors describe 2 different growing myxomatous aneurysms in a child successfully managed using a combined multidisciplinary approach. A 12-year-old boy developed a sudden headache, diplopia, gait instability, and speech difficulty. Magnetic resonance imaging revealed a left parietal hemorrhage and multifocal cerebral infarction, suspicious for an embolic etiology. A cardiac myxoma was identified in the left atrium and resected. Follow-up cranial vasculature imaging demonstrated multiple intracranial myxomatous aneurysms. These lesions were followed up, and serial imaging identified marked growth of 2 of them (right occipital and left parietal), prompting invasive intervention. The deep occipital lesion was better suited to endovascular treatment, while the superficial parietal lesion was amenable to resection. The patient underwent embolization of an enlarging fusiform aneurysm of the distal right posterior cerebral artery, followed by a left parietal craniotomy for a lesion of the distal left middle cerebral artery. Both procedures were performed without complications and achieved successful obliteration of the lesions, as confirmed by catheter angiography at the 30-month follow-up. To the authors' knowledge, this report illustrates the first combined endovascular and open surgical treatment of 2 myxomatous aneurysms in a single patient. While acknowledging the rarity of this condition, this report illustrates the clinical manifestations and treatment challenges posed by myxoma and details a successful strategy that could be employed in similar scenarios.

Somatic PIK3CA mutations are present in multiple tissues of facial infiltrating lipomatosis.

BackgroundFacial infiltrating lipomatosis (FIL) is a congenital disorder that causes overgrowth of one side of the face. The purpose of this study was to determine whether PIK3CA mutations are present in tissues outside of the subcutaneous adipose.MethodsFIL tissues from three patients were dissected to enrich for cells from skin, subcutaneous tissue, orbicularis oris muscle, buccal fat, zygomatic bone, and mucosal neuroma. Endothelial cells within the affected tissue also were enriched using CD31 microbeads. Laser capture microdissection on formalin-fixed paraffin-embedded histologic sections was performed to collect specific cell types. DNA was extracted from each tissue and cell type, and measured for the abundance of mutant PIK3CA alleles using droplet digital PCR.ResultsWe detected mutant PIK3CA alleles in every tissue and cell type tested from each overgrown face; frequencies ranged from 1.5 to 53%. There were fewer mutant endothelial cells compared with nonendothelial cells, and the stromal cell compartment had the highest frequency of mutant cells in each tissue.ConclusionsPIK3CA mutations are not restricted to a single tissue or cell type in FIL. Overgrowth in this condition is likely due to the mutation arising in a cell that contributes to several different facial structures during embryogenesis.

Somatic Activating Mutations in GNAQ and GNA11 Are Associated with Congenital Hemangioma.

Congenital hemangioma is a rare vascular tumor that forms in utero. Postnatally, the tumor either involutes quickly (i.e., rapidly involuting congenital hemangioma [RICH]) or partially regresses and stabilizes (i.e., non-involuting congenital hemangioma [NICH]). We hypothesized that congenital hemangiomas arise due to somatic mutation and performed massively parallel mRNA sequencing on affected tissue from eight participants. We identified mutually exclusive, mosaic missense mutations that alter glutamine at amino acid 209 (Glu209) in GNAQ or GNA11 in all tested samples, at variant allele frequencies (VAF) ranging from 3% to 33%. We verified the presence of the mutations in genomic DNA using a combination of molecular inversion probe sequencing (MIP-seq) and digital droplet PCR (ddPCR). The Glu209 GNAQ and GNA11 missense variants we identified are common in uveal melanoma and have been shown to constitutively activate MAPK and/or YAP signaling. When we screened additional archival formalin-fixed paraffin-embedded (FFPE) congenital cutaneous and hepatic hemangiomas, 4/8 had GNAQ or GNA11 Glu209 variants. The same GNAQ or GNA11 mutation is found in both NICH and RICH, so other factors must account for these tumors' different postnatal behaviors.

Impact of Screening for Hepatic Hemangiomas in Patients with Multiple Cutaneous Infantile Hemangiomas.

OBJECTIVES: Hepatic hemangiomas are often found in association with multiple cutaneous infantile hemangiomas. Screening abdominal ultrasonography has been recommended for patients with five or more cutaneous lesions. We sought to determine whether hemangiomas found through screening had improved clinical outcomes. METHODS: Patients entered into our hepatic hemangioma registry between 1995 and 2012 were reviewed. RESULTS: Seventy-two patients with multiple cutaneous and hepatic hemangiomas were identified; 43 (60%) were detected through screening. The median age at diagnosis was 41 days for screened patients and 53 days for those not screened. Screening detected 40 (93%) multifocal and 3 (7%) diffuse hemangiomas, compared to 18 (62%) and 11 (38%), respectively, in the nonscreened group. Patients identified by screening had lower incidences of congestive heart failure and hypothyroidism and were less likely to receive treatment for their hemangiomas. The mortality rate in the children not screened was 28% (n = 8). None of the patients found by screening died (p < 0.001). Multivariate analysis of treated patients demonstrated that screening was a significant predictor of reduced mortality (p = 0.04). CONCLUSION: Hepatic hemangiomas found through screening ultrasonography are less likely to develop serious clinical sequelae. Although the reasons for this may include detection of hemangiomas that are less likely to progress to symptomatic disease, it appears that it also allows for earlier intervention for more concerning (e.g. diffuse) subtypes. Screening may allow for closer surveillance and earlier treatment before life-threatening progression in a subset of infants with liver hemangiomas, preventing complications and reducing mortality.

Yolk Sac Tumor of the Testis in Infants and Children: A Clinicopathologic Analysis of 33 Cases.

We report 33 pure yolk sac tumors of the testis from boys 5 to 71 months of age (mean 20.7 mo) diagnosed from 1918 to 2014. All except 1 underwent orchiectomy, with lymph node dissections (all negative) performed in 18; 21 also received chemotherapy and 12 radiotherapy. The tumors were 1.6 to 7.0 cm (mean 3.7 cm) and were nonencapsulated, with a gray to yellow, often mucoid, cut surface. The commonest pattern was reticular-microcystic, but macrocystic, papillary, endodermal sinus (Schiller-Duval bodies), labyrinthine, myxomatous, glandular, and solid patterns were also observed. Follow-up was available for 32 patients (mean 100.5 mo; range, 3 to 456 mo). Twenty-four patients (including 4 who did not receive adjuvant therapy) were without evidence of disease, 8 had metastatic disease; 5 of the latter died of tumor and 1 of treatment complications. Two patients with metastasis were cured with radiation with or without chemotherapy. Two or more of the following were associated with a poor outcome in patients presenting with stage I cases: tumor size >4.5 cm (4/6 tumors [67%]), invasion of rete testis and/or epididymis (3/7 tumors [43%]), and necrosis (6/17 tumors [35%]). In the nonmetastasizing group, 2 or more unfavorable features occurred in only 3/24 tumors (13%) (P=0.0001). It is crucial that this tumor be distinguished from the juvenile granulosa cell tumor, which occurs at a slightly younger age and has distinctive features, although there may be some morphologic overlap. The survival of young boys with testicular yolk sac tumor is very good because of both effective chemotherapy and likely, the inherent characteristics of the tumor in this age group.

A somatic MAP3K3 mutation is associated with verrucous venous malformation.

Verrucous venous malformation (VVM), also called "verrucous hemangioma," is a non-hereditary, congenital, vascular anomaly comprised of aberrant clusters of malformed dermal venule-like channels underlying hyperkeratotic skin. We tested the hypothesis that VVM lesions arise as a consequence of a somatic mutation. We performed whole-exome sequencing (WES) on VVM tissue from six unrelated individuals and looked for somatic mutations affecting the same gene in specimens from multiple persons. We observed mosaicism for a missense mutation (NM_002401.3, c.1323C>G; NP_002392, p.Iso441Met) in mitogen-activated protein kinase kinase kinase 3 (MAP3K3) in three of six individuals. We confirmed the presence of this mutation via droplet digital PCR (ddPCR) in the three subjects and found the mutation in three additional specimens from another four participants. Mutant allele frequencies ranged from 6% to 19% in affected tissue. We did not observe this mutant allele in unaffected tissue or in affected tissue from individuals with other types of vascular anomalies. Studies using global and conditional Map3k3 knockout mice have previously implicated MAP3K3 in vascular development. MAP3K3 dysfunction probably causes VVM in humans.

Risk factors for mortality in patients with multifocal and diffuse hepatic hemangiomas.

PURPOSE: Multifocal and diffuse hepatic hemangiomas are true infantile hemangiomas, which likely exist in a continuum. We reviewed our hepatic hemangioma registry to identify prognostic indicators for mortality. METHODS: Registry records entered between 1995 and 2012 were reviewed. Clinical characteristics were evaluated for prognostic significance using the multivariable Cox proportional hazards model. Survival data were analyzed using the Kaplan-Meier product-limit method. RESULTS: We identified 123 patients with multifocal (n=91) and diffuse (n=32) hepatic hemangiomas. Mortality was 16% (n=20); 40% (n=8) had multifocal and 60% (n=12) had diffuse lesions. A diagnosis of diffuse disease (hazard ratio: 9.9, 95% CI: 2.0-50.8, P=.002) and congestive heart failure (CHF) (hazard ratio: 3.9, 95% CI: 1.3-14.2, P=.031) were significant risk factors for mortality across the continuum; age at presentation, cardiomegaly, presence of shunts, and hypothyroidism were not statistically significant independent risk factors. Among patients with diffuse lesions, eight (67%) who died had abdominal compartment syndrome, which was also associated with mortality (P=.002). CONCLUSIONS: Hepatic hemangioma patients with CHF or diffuse disease are at higher risk for mortality. Patients with multifocal lesions without CHF may go undetected until lesions become diffuse. Aggressive treatment of symptomatic patients and close follow-up of asymptomatic patients may improve mortality.

Lymphatic and other vascular malformative/overgrowth disorders are caused by somatic mutations in PIK3CA.

OBJECTIVES: To test the hypothesis that somatic phosphatidylinositol-4,5-bisphospate 3-kinase, catalytic subunit alpha (PIK3CA) mutations would be found in patients with more common disorders including isolated lymphatic malformation (LM) and Klippel-Trenaunay syndrome (KTS). STUDY DESIGN: We used next generation sequencing, droplet digital polymerase chain reaction, and single molecule molecular inversion probes to search for somatic PIK3CA mutations in affected tissue from patients seen at Boston Children's Hospital who had an isolated LM (n = 17), KTS (n = 21), fibro-adipose vascular anomaly (n = 8), or congenital lipomatous overgrowth with vascular, epidermal, and skeletal anomalies syndrome (n = 33), the disorder for which we first identified somatic PIK3CA mutations. We also screened 5 of the more common PIK3CA mutations in a second cohort of patients with LM (n = 31) from Seattle Children's Hospital. RESULTS: Most individuals from Boston Children's Hospital who had isolated LM (16/17) or LM as part of a syndrome, such as KTS (19/21), fibro-adipose vascular anomaly (5/8), and congenital lipomatous overgrowth with vascular, epidermal, and skeletal anomalies syndrome (31/33) were somatic mosaic for PIK3CA mutations, with 5 specific PIK3CA mutations accounting for ∼ 80% of cases. Seventy-four percent of patients with LM from Seattle Children's Hospital also were somatic mosaic for 1 of 5 specific PIK3CA mutations. Many affected tissue specimens from both cohorts contained fewer than 10% mutant cells. CONCLUSIONS: Somatic PIK3CA mutations are the most common cause of isolated LMs and disorders in which LM is a component feature. Five PIK3CA mutations account for most cases. The search for causal mutations requires sampling of affected tissues and techniques that are capable of detecting low-level somatic mosaicism because the abundance of mutant cells in a malformed tissue can be low.

Villin immunohistochemistry is a reliable method for diagnosing microvillus inclusion disease.

Microvillus inclusion disease (MVID) is a rare congenital disorder that manifests early in infancy as intractable watery diarrhea. The entity is characterized morphologically by a deficient brush border and apical cytoplasmic inclusions within absorptive cells (enterocytes) due to misplaced assembly of brush border proteins. The diagnosis is based upon histopathology, special stains, immunohistochemistry (IHC), and ultimately upon electron microscopy. Currently, the periodic acid-Schiff stain (PAS) and CD10 IHC are commonly used as adjuncts, but in addition to brush border structures, they stain a variety of apical cytoplasmic inclusions and organelles, thereby interfering with recognition of microvillus inclusions. Villin is a protein that specifically binds to the actin core bundle of microvilli. We utilized villin IHC in formalin-fixed paraffin-embedded gastrointestinal biopsies from 6 patients with MVID, 5 with celiac disease, and 17 children with normal intestinal biopsies and compared the results with those obtained with CD10 IHC and PAS staining. All MVID cases had confirmatory electron microscopy at the time of diagnosis. Villin immunoreactivity was restricted to the brush border in the control groups. In MVID, villin IHC showed attenuation or loss of the surface brush border and also highlighted the cytoplasmic microvillus inclusions with clarity. In MVID, CD10 IHC and the PAS stain also showed attenuation or loss of the surface brush border, but staining of a variety of cytoplasmic structures largely obscured the microvillus inclusions. In sum, villin IHC is a reliable and superior adjunct in the diagnosis of MVID. Study of additional cases will determine whether villin IHC would obviate the need for electron microscopic confirmation.

Subfascial involvement in glomuvenous malformation.

OBJECTIVE: Glomuvenous malformation (GVM) is an inherited autosomal dominant trait. The lesions, which appear as bluish nodules or plaque-like cutaneous elevations, are usually tender and more firm than sporadic venous malformations. Conventionally, the lesions are thought to be limited to the cutaneous and subcutaneous tissue planes. The objective was to characterize the depth of involvement of GVM lesions. MATERIALS AND METHODS: Magnetic resonance imaging (MRI) findings in GVM were retrospectively evaluated by two radiologists. The signal characteristics, tissue distribution, pattern of contrast enhancement of the lesions in GVM were documented. RESULTS: Thirty patients (19 female) aged 1-35 years (mean 18 years) were diagnosed with GVM based on clinical features (n = 20) and/or histopathological findings (n = 10). The lesions were present in the lower extremity (n = 15), upper extremity (n = 6), cervico-facial region (n = 6), pelvis (n = 2), and chest wall (n = 1). All patients had skin and subcutaneous lesions. Fifty percent of the patients (n = 15) demonstrated subfascial intramuscular (n = 15), intra-osseous (n = 1), and intra-articular involvement (n = 1). CONCLUSION: Contrary to the conventional belief that GVMs are generally limited to the skin and subcutaneous tissue, deep subfascial extension of the lesions is common.

Kaposiform lymphangiomatosis: a distinct aggressive lymphatic anomaly.

OBJECTIVE: To describe the clinical and imaging characteristics of a new lymphatic disorder with a unique histological pattern and poor prognosis. STUDY DESIGN: An observational, retrospective study identified and characterized 20 patients with distinct lymphatic histopathology referred to the Vascular Anomalies Center at Boston Children's Hospital between 1995 and 2011. RESULTS: The median age at onset was 6.5 years (range, birth to 44 years). Clinical and radiologic findings suggested a generalized process. The most common presentations were respiratory symptoms (50%), hemostatic abnormalities (50%), and an enlarging, palpable mass (35%). All patients had mediastinal involvement; 19 patients developed pericardial (70%) and/or pleural effusions (85%). Extrathoracic disease manifested in bone and spleen and less frequently in abdominal viscera, peritoneum, integument, and extremities. Despite aggressive procedural and medical therapies, the 5-year survival was 51% and the overall survival was 34%. Mean interval between diagnosis and death was 2.75 years (range, 1-6.5 years). CONCLUSIONS: We describe a clinicopathologically distinct lymphatic anomaly. We propose the term kaposiform lymphangiomatosis (KLA) because of characteristic clusters or sheets of spindled lymphatic endothelial cells accompanying malformed lymphatic channels. The intrathoracic component is most commonly implicated in morbidity and mortality; however, extrathoracic disease is frequent, indicating that KLA is not restricted to pulmonary lymphatics. The mortality rate of KLA is high despite aggressive multimodal therapy.