Vascular Tumors

16.2.1 WHO Classification

16.2.2 ISSVA Classification

Other entities, such as glomus tumors and synovial hemangiomas, will be discussed separately.

16.3.1 Benign Vascular

We will only describe the most common lesions and those associated with clinical or specific nosological entities.

16.3.1.1 Infantile Hemangioma (IH)

Infantile hemangiomas are the most common vascular tumor of infancy [10]. They occur three to five times more frequently in females compared to males [14] and may be present at birth but are frequently diagnosed by 3 months of age [10]. In most cases, diagnosis is made clinically through the observation of a subcutaneous bluish red mass that looks like the surface of a strawberry (Fig. 16.1).

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These tumors undergo two biologic phases:

• The proliferative phase, which is characterized by rapid endothelial growth in the first few months of life that stabilizes in size at approximately 9–10 months of age. Reflecting the characteristic high-flow component of this phase, the tumor manifests as a pulsatile and warm mass [15].

• The involuting phase, which occurs over the next several years, is a period during which the hemangioma spontaneously decreases in size and is replaced by a residual fibrofatty mass [16]. This process is usually completed by 7–10 years of age [17].

On pathological examination, whatever the phase, IHs express a unique immunophenotype (glucose transporter protein-1 (GLUT1)), which differentiates them from other vascular lesions [18].

Infantile hemangiomas are most commonly seen on the face and neck (60 % of cases), followed by the trunk (25 %) and extremities (15 %) [19]. They are multifocal in approximately 30 % of the cases [1].

During the proliferative phase, the lesion appears as a well-defined mass with variable echogenicity. The vessels may be visible using US. Doppler demonstrates a characteristic hypervascular lesion with a high density of vessels (arteries and veins) and a low resistance on spectral analysis (Fig. 16.2) [2, 20]. Despite the high-flow nature of the lesion during this phase, there is a distinct soft tissue lesion that usually contains a single afferent artery and no direct arteriovenous shunting, unlike arteriovenous malformations [2]. During the involuting phase, IHs appear hyperechoic with a low density of vessels.

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The appearance of IHs using MR imaging is indicative of their biologic phase. The proliferative phase is characterized by a well-circumscribed lobulated lesion with low or iso-signal intensity on the T1-weighted images and a high signal intensity on the T2-weighted images; the IH lesions also show an early and homogeneous enhancement after gadolinium administration (Fig. 16.2) [21]. Fast-flow vessels appearing as flow voids can be depicted within and around the lesion [2]. During the involuting phase, the increasing amount of fat within the tumor increases the signal intensity of the lesion on the T1-weighted images, which is associated with less avid contrast enhancement (Fig. 16.3).

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The presence of a high resistance index on the spectral analysis or a marked perilesional edema on the T2-weighted images is suggestive of other tumoral lesions, such as sarcomas, neuroblastomas, myofibromatosis, tuft hemangiomas, metastatic neuroblastomas, or other tumors [2].

Multiple hemangiomas of the skin are usually linked with visceral hemangiomas. Segmental hemangiomas may be associated with PHACE syndrome (see Sect. 16.6.1) [22]. Most of these segmental hemangiomas are telangiectatic or reticular and do not demonstrate a high-flow pattern on Doppler US.

In the majority of the cases, no treatment is required due to spontaneous involution. However, 10–20 % of the cases require treatment, including cases with periocular location with vision compromise, high-output cardiac failure, ulceration, compression of the airway, facial hemangiomas with rapid growth and distortion, and symptomatic muscular hemangiomas. Medical treatment is usually attempted first, and propranolol is typically the first-line therapy with excellent results in most cases [23]. Other treatments include corticosteroids, vincristine, interferon, and laser therapy. Surgery is required when medical alternatives are ineffective, mostly in cases involving function-threatening, life-endangering, and disfiguring lesions [16].

Key Points

• Infantile hemangioma.

• The most common vascular tumor of infancy.

• Characterized by two biologic phases (proliferative/involuting).

• Positive for the GLUT1 marker at both stages.

• Presence of a high-flow soft tissue mass.

• If perilesional edema is present, other tumoral lesions must be ruled out.

16.3.2 Intermediate and Malignant Vascular Tumors

16.3.2.2 Kaposi’s Sarcoma

Kaposi’s sarcoma (KS), also known as KS-associated herpesvirus (KSHV), is a locally aggressive vascular tumor associated with the human herpesvirus-8 (HHV-8). This tumor is probably of lymphatic origin and is characterized by neoangiogenesis and proliferation of spindle-shaped cells with inflammation and edema [33]. It is usually a multicentric disease that originates in the lymphoreticular system and may involve the skin, lymph nodes, lungs, gastrointestinal tract, liver, spleen, and musculoskeletal system. Four types of KSs have been described: classic KS (chronic form, patients older than 60 years old), endemic KS (middle-aged adults and children, African KS), KS in iatrogenically immunosuppressed patients (related to solid organ transplantation or immunosuppressive therapy), and AIDS-related KS [28, 33]. The topography of the lesions and their aggressivity depend on the type of KS. For example, KS AIDS is often aggressive and multifocal (face, genitals, lung, lower extremities). Imaging depends on the location of the lesion and the lymph nodes are typically hypervascular (Fig. 16.5) [28, 33].

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16.3.2.4 Angiosarcoma

Angiosarcoma is a high-grade malignant tumor with a high mortality rate [39]. It may involve the skin (33 % of the cases), the deeper soft tissues (24 % of the cases), the internal organs, or the bones [38]. The presence of chronic lymphedema (Stewart-Treves syndrome) occurs in approximately 10 % of the cases and is a well-known risk factor for angiosarcoma [38]. Stewart-Treves syndrome is usually reported in the upper extremities after a mastectomy for breast cancer. Additionally, it can be seen in the lower extremities after hysterectomy for uterine cancer, trauma, or infection [40]. Angiosarcoma is rarely radiation-induced, and it exceptionally arises in vascular lesions [41]. Clinically, two types of angiosarcoma can be seen:

• A cutaneous form (purplish red plate, possibly nodular)

• A deep form (painful soft tissue mass in the lower limbs) [5, 39]

Metastasis most frequently involves the lung and lymph nodes, followed by the liver, the bones, and the soft tissues [39]. The imaging appearance depends on whether the lesion is located superficially or deep. Skin thickening or focal soft tissue nodules are observed when the lesion involves the skin and subcutaneous tissues. The imaging features are not specific and include intermediate echogenicity, variable signal intensity on T2-weighted images, and variable contrast enhancement (Fig. 16.6) [28]. When the lesion is associated with chronic lymphedema, extremity enlargement, diffuse skin thickening, and edema of the subcutaneous connective tissue can be seen (Fig. 16.7).

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16.4.1 Venous Malformations (VMs)

VMs represent the most common peripheral vascular malformation [43, 44]. They can be simple, combined (e.g., capillary-venous and capillary-lymphaticovenous malformations), or syndromic (associated with Klippel-Trenaunay syndrome, blue rubber bleb nevus syndrome, or Maffucci syndrome). They are present at birth, but patients usually develop symptoms during late childhood or early adulthood (especially during puberty and pregnancy). They vary in size and shape and can be localized and well defined or diffuse and infiltrative. They can involve the superficial and/or deep tissues. When superficial, patients typically demonstrate bluish skin abnormalities and a soft compressible and nonpulsatile soft tissue mass [45]. They typically expand during the Valsalva maneuver and decompress with extremity elevation and local compression [17, 45]. They can also be deep, involving many anatomical structures, including the muscle, synovial membrane, bone, and liver [4, 45, 46]. They may cause pain, impaired mobility, and skeletal deformities. They are usually located on the extremities (40 %), head and neck (40 %), and trunk (20 %) [17, 45]. Elevated D-dimer levels are a specific biomarker for VMs [47].

Pathologically, VMs are characterized by small- or large-sized venous channels connected with the normal venous system. They may contain thrombi whose dystrophic mineralization produces phleboliths [43]. Although pathologists now apply the new ISSVA nomenclature [46, 48], the historical terminology is kept in the current WHO classification (Table 16.1) [5]. Therefore, entities such as cavernous, venous, or intramuscular hemangiomas usually correspond to venous malformations and are still frequently used in pathologic reports using the WHO classification [5, 38, 46].

Phleboliths and dystrophic calcifications are easily detected on radiographs and CT and are highly suggestive of VMs (Fig. 16.8) [2]. In case of extensive malformations, the involvement of the adjacent joints or bones is possible, such as cortical erosion, periosteal reaction, regional osteopenia, and bony overgrowth [49, 50].

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Ultrasound shows an extremely variable appearance of the lesion, ranging from predominantly solid to multicystic lesions [1]. VMs can be well defined or infiltrative. These usually hypoechoic and heterogeneous lesions consist of tubular vascular or cavity compressible areas, reflecting the presence of vessels. The phleboliths are usually seen as hyperechoic foci. After applying compression, the movement of blood into the cavities can be identified (Fig. 16.9). Doppler US typically shows no flow or low-velocity flow. In the absence of a spontaneous vascular signal, dynamic maneuvers such as the Valsalva maneuver or manual compression by the probe followed by its decompression can cause the appearance of vascular signal although thrombosis is possible.

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MRI is an excellent imaging modality to define the extent of the lesions and their relationship with the adjacent structures. VMs demonstrate well- or ill-defined limits, but they typically do not produce any significant soft tissue mass syndrome, which suggests diagnosis. Vascular vessels are seen as tubular and serpiginous cavities with hypo- to iso-signal intensity on T1-weighted images and strong hyper-signal intensity on T2-weighted images, separated by hyperechoic fat (Fig. 16.10). Fat-suppressed T2-weighted images are particularly useful to evaluate the extent of the VMs. Phleboliths appear as small low-signal-intensity foci on all pulse sequences. Sometimes fluid-fluid levels due to hemorrhage or high protein content can be seen (Fig. 16.11) [1], though they are less common compared to lymphatic malformations. Contrast-enhanced 3-D acquisitions after dynamic gadolinium administration should be performed to evaluate the perfusion of the malformation and its drainage into the venous system. VMs are characterized by a lack of arterial and early venous enhancements and the absence of enlarged feeding vessels or arteriovenous shunting. They typically demonstrate a slow and progressive enhancement. Characteristic nodular enhancement of tortuous vessels can be observed on delayed venous phase images (Fig. 16.12) [3, 51]. The time between the beginning and the maximal enhancement is between 50 and 100 s [52]. Less specific appearances may be encountered when the lesion is composed of small vessels (Fig. 16.13) or in the absence of adipose tissue [53]. Intramuscular VMs often demonstrate serpiginous venous channels between the muscle fibers that are oriented along the long axis of the involved muscle [1]. Intra-articular involvement may lead to chronic hemarthrosis and joint destruction [54, 55] (Fig. 16.14). Localized intravascular coagulopathy is more frequent in diffuse compared to focal VMs and can be responsible for pain and thrombosis [56].

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Most VMs are managed conservatively with a compression bandage of the extremity and medical antalgics for pain. In cases of major pain, joint involvement, and functional or cosmetic problems, the first-line treatment for VMs is sclerotherapy (dehydrated ethanol, sodium tetradecyl sulfate, polidocanol, and bleomycin), which can be followed by resection, laser therapy, and photodynamic therapy [57, 58].

16.4.2 Lymphatic Malformations (LMs)

Pathologically, they are composed of serpiginous dilated lymphatic channels that do not communicate with the normal lymphatic system [45], except in the retroperitoneum. Macrocystic and microcystic lesions are pathologically indistinguishable [61]. Diagnosis is suggested after a positive test for markers of lymph vessels, such as the vascular endothelial growth factor receptor 3 (VEGFR-3), LYVE-1, D2-40, and podoplanin [61, 62, 63]. However, it should be kept in mind that LMs can be associated with the other vascular malformations.

LMs are present at birth in half of the patients (prenatal diagnosis of macrocystic types is possible) and are diagnosed before the age of 2 years in 90 % of the cases [61, 64]. They mainly involve the head and neck (55–95 %) and axillary regions (20 %) with a predilection for the left side of the body [64]. They can affect multiple structures (lung, intestine, liver, spleen, etc.) including the bones [38]. Macrocystic LMs are typically large and clinically manifest as a soft swelling mass with a rubbery consistency. They are well limited and mobile under a normal skin [57, 64]. Transillumination confirms the liquid nature of the lesion. The majority of the cases are asymptomatic, but complications, such as local compression, sudden increase in size secondary to bleeding (trauma), or infection from an adjacent process of the head and neck, can occur [65].

Microcystic LMs tend to infiltrate the adjacent structures. They are sometimes associated with a particular skin damage (lymphangioma circumscriptum) [1, 2, 61]. More unusual locations include the mediastinum, retroperitoneum, omentum, mesentery, and bones [66].

Ultrasound demonstrates a multiloculated cystic mass and the size of the cavity determines the type of LM. The cystic spaces are mostly anechoic or hypoechoic, but levels may be observed in cases of bleeding, infection, or chylous fluid. Septa of variable thickness correspond to clusters of lymph structures. LMs do not demonstrate any associated vascularity, soft tissue components, or perilesional inflammatory changes. Calcifications are sometimes observed.

On MRI, LMs are usually seen as lobulated cystic masses with iso- to hypo-signal intensity on T1-weighted images and increased signal intensity on T2-weighted and STIR sequences (Fig. 16.15). Fluid levels can be observed in cases of superimposed hemorrhage or infection [3]. After contrast administration, macrocystic LMs exhibit rim and septal enhancement [15, 44], whereas microcystic LMs do not show any enhancement (Fig. 16.16) [15]. However, combined lymphatic-venous malformations may show diffuse enhancement, which is related to the venous component enhancement in mixed malformations [3]. MRI is the best imaging modality to assess the exact extent of the lesion, which may be localized or diffuse and very infiltrative [1]. Involvement of the adjacent bone may be present (Fig. 16.16). Needle aspiration confirms the diagnosis of LMs by finding lymphatic vessels.

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The first-line therapy is percutaneous sclerotherapy, usually with absolute alcohol under radiological control. Several sessions are needed in extensive forms of LM. As this treatment is usually effective in macrocystic LMs, surgery is less frequently proposed [57]. Microcystic LMs are more difficult to treat and recurrence is more frequent. They should be managed conservatively as much as possible [2].

16.4.3 Capillary Malformations (CMs)

These intradermal vascular lesions are composed of mature ectatic capillary channels and are hemodynamically inactive. The diagnosis of CMs is clinically based on the appearance of a cutaneous red discoloration [9]. CMs are present at birth in 0.3 % of children [15], and they typically regress. They usually involve the face but can develop anywhere. They can be associated with malformation syndromes, such as Sturge-Weber syndrome, Klippel-Trenaunay syndrome, and Parkes Weber syndrome. Nonspecific thickening of the skin can be observed with US or MRI [1].

16.4.4 Arteriovenous Malformations (AVMs)

AVMs are high-flow vascular malformations related to an abnormal communication between arteries and veins, with persistence of fetal capillary beds [8]. They are usually sporadic but can be seen in hereditary syndromes [26, 67]. They most often affect the head and neck region (including the brain), the extremities, and the internal organs [5]. They are present at birth in an early quiescent stage and usually do not become evident before until later childhood or adulthood. Like the other vascular malformations, they generally increase in size proportional to the growth of the child and are under hormonal influences (puberty, pregnancy). Their size can also be influenced by trauma (such as biopsy or incomplete surgery) [17, 45]. They are hemodynamically active, which can result in a red, pulsatile, warm mass with dilated superficial draining veins [68]. The presence of the shunt may induce limb hypertrophy and reflex bradycardia after compression of the lesion. Adjacent bone or joint damage is possible (marked periosteal reaction or destruction) [2, 26].

The histology of AVMs is highly variable with a combination of capillaries, venules, and arterioles in a fibrous or fibromyxoid stroma. Correlation with imaging is important for the diagnosis of AVMs. Calcifications and thrombosis are possible [5].

On US, AVMs are seen as ill-defined areas formed by multiple juxtaposed tortuous vessels, separated by hyperechoic fat. The vessels include arteries with diastolic flow and arterialized draining veins with pulsatile flow (not seen in hemangiomas) [17]. The nidus is recognized by its various vascular areas and aliasing phenomena in terms of the color Doppler shunts [20].

MR imaging demonstrates tortuous structures composed of enlarged feeding arteries and draining veins without well-defined associated mass. Signal voids are observed in these vessels on both T1-W and T2-W SE sequences (Fig. 16.17), but high signal intensity is seen on gradient-echo sequences, indicating high-flow lesions [1, 45]. Gadolinium perfusion allows for the mapping of feeding arteries, draining veins, and the nidus [1]. Early venous filling is typically seen in AVMs (Fig. 16.18). The dynamic opacification, using time-resolved MR angiography, confirms the rapid flow when the period between the start and the maximal enhancement is 5–10 s [3, 52]. Intraosseous extension of the lesion can also be seen [68]. Arteriography is only performed when the MR features are equivocal or when embolization is considered. This technique has the advantage of selective catheterization of the feeding arteries with depiction of the nidus and early draining veins.

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The goal of treatment for AVMs is the eradication of the nidus, causal factor of the shunt. Treatment includes two stages, a preoperative embolization by a biological glue and a complete surgical excision [57]. Different surgical approaches have been described, including arterial microcatheterism, direct percutaneous puncture, and retrograde venous microcatheterism [45].

16.5.1 Glomus Tumor (GT)

According to the latest revision of the WHO classification (2013), glomus tumor is regarded as a pericystic (perivascular) tumor (see also Chaps.  11 and  15).

Glomus tumors and its rare variants, such as glomangioma (20 % of cases), glomangiomyoma (less than 10 % of cases), and the exceptional malignant glomus tumor [69], are derived from neuromyoarterial glomus bodies. These millimeter organs are involved in thermoregulation by modulation of cutaneous blood flow. They are mainly localized in the dermis, at the ends of fingers and toes, and especially under the nails [38, 70]. The most common location for GTs is the tip of the fingers, particularly the subungual area where it can lead to erosion of the adjacent phalanx [71]. They are less common in the pulp. They are mainly observed in adults and are observed as a small red-blue superficial nodule (1 mm−3 cm), with extremely intense focal pain, triggered by pressure and cold [70]. This clinical presentation results in diagnosis in 90 % of the cases when the digits are involved [72]. Subungual lesions have female predilection in contrast to the other locations [70, 73]. Other rare locations include muscles, tendons, nerves, bones, and viscera [74, 75, 76] and involve less specific symptoms [70].

On radiography, finger involvement is accompanied by bone erosion of the distal phalanx in approximately one-third of the cases [72]. GTs can be visualized using MRI or ultrasound, although they typically measures only 1.5–2 mm [77, 78]. Ultrasound shows a well-limited hypoechoic nodule which often contains small cystic internal rearrangements and a significant hyperemia on Doppler (Fig. 16.19) [79]. On MRI, dedicated coils and very thin sections with excellent spatial resolution should be used. GTs show with hypo- to iso-signal intensity on T1-weighted images and strong hyper-signal intensity on T2-weighted images (Fig. 16.20) [28, 75]. MR angiography shows intense enhancement in the arterial phase with tumor blush [71, 78, 80]. This is sometimes the sole sequence showing the lesion. Small lesions enhance homogeneously after gadolinium administration, while larger GTs are more heterogeneous on T2-weighted images and after contrast administration [79]. The histologic subtype of the lesion (vascular, solid, myxoid) also influences its appearance on T1-weighted images (from low to high signal intensity) [71]. Postsurgical recurrences present the typical appearance of GTs in half of the cases [78]. The main differential diagnoses include mucoid cysts, venous malformations, malignant melanomas, soft tissue chondromas, giant cell tumors, and epidermoid cysts [71, 75, 78, 80].

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Surgical excision must be complete to be effective for pain and prevent recurrences (4–20 % in the subungual location) [77].

16.5.2 Synovial Hemangioma (SH)

SHs are rare vascular lesion of the synovial membrane that affect children and young adults, and 75 % of patients are symptomatic before the age of 16 years [81]. SHs mainly develop in the knee (60 %), particularly at the suprapatellar pouch. Other locations include the elbow (30 %), ankle, hip, temporomandibular joint, and tendon sheaths [81, 82]. SH may be associated with repetitive episodes of pain, swelling, and joint effusion (hemarthrosis). With time, limitation of the joint mobility and muscle atrophy can develop. Joint blocking is possible when the lesion is pedunculated. A diagnostic delay is common, and because of the repetitive bleeding into the joint, an arthropathy similar to the hemophilic arthropathy can develop. If arthrography is performed, the synovium may demonstrate irregular contours mimicking synovial chondromatosis, villonodular synovitis, or rheumatoid arthritis [82]. MRI is the best imaging modality to identify this lesion and to assess its intra- and extraarticular extent (Fig. 16.21). MRI features are usually pathognomonic: serpiginous lesion with a low or iso-signal intensity on T1-weighted images and high signal intensity on T2-weighted images due to vascular stasis, associated with fibrofatty septa and sometimes vascular structures (thrombosed or not). SH lesion enhances after gadolinium administration, sometimes heterogeneously. Joint effusion and erosive changes of the subchondral bone are often associated [83, 84].

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Early surgical excision is mandatory to prevent the development of arthropathy.

16.6.1 PHACE Syndrome

PHACE is an acronym for the syndrome’s most common clinical and imaging findings: posterior fossa malformations, segmental infantile hemangiomas of the face and neck (usually larger than 5 cm), arterial anomalies, cardiac defects or coarctation of the aorta, eye or endocrine anomalies, and sternal defects [67, 87].

16.6.2 PELVIS and SACRAL Syndromes

Evaluation with MRI is therefore recommended for such lesions in this particular location [88, 89].

16.6.3 Kasabach-Merritt Syndrome

Kasabach-Merritt syndrome is characterized by a combination of vascular lesions (kaposiform hemangioendotheliomas, tufted angiomas), thrombocytopenia, and coagulopathy causing hemorrhage, infections, and multiple organ failure [67]. The mortality rate is close to 30 % [38], and aggressive therapy is required (steroids, vincristine, and interferons).

16.6.4 Klippel-Trenaunay Syndrome

Klippel-Trenaunay syndrome is a non-hereditary complex disorder usually affecting only one of the lower extremities, but it can spread into the pelvis and trunk. It is defined by three classic clinical findings: (1) capillary malformation (usually of affected limb), (2) bone and soft tissue limb enlargement (usually affecting one extremity), and (3) atypical varicosities or venous malformations with a characteristic abnormal lateral vein beginning at the ankle and extending to the pelvic region (Fig. 16.22) [67, 90].

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Abnormal development of the deep and superficial veins explains persistent embryonic veins including lateral veins with persistent sciatic vein and dilated superficial system. Hypertrophy is variable, affecting the whole leg or only the distal digits [91]. Syndactyly, polydactyly, and congenital hip dislocation can also be observed [92].

On imaging, vascular overgrowth demonstrates slow and late enhancement indicating low-flow malformations. Deep venous malformations of the femoral vein are commonly seen. Because of overgrowth of the soft tissues, the affected limb is usually larger and longer than the unaffected limb [86].

16.6.5 Maffucci Syndrome

Maffucci syndrome is a rare and non-hereditary syndrome characterized by the association of multiple enchondromas and multiple low-flow vascular malformations (mainly venous, rarely lymphatic) [93]. Clinically, it manifests before 1 year of age in 25 % of the patients and by the puberty in 80 % of all cases [67].

Enchondromas usually involve the phalanges of the hands (Fig. 16.23) and feet, and in one-half of the patients, lesions are unilateral and lead to the development of notable malformations [93]. Low-flow vascular malformations do not have the same distribution as enchondromas and usually involve the subcutaneous soft tissues of another anatomic region. Phleboliths are very suggestive [94].

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The malignant transformation rate is high and involves enchondromas (chondrosarcoma) in 15–20 % of the patients [95] or vascular malformations (angiosarcoma) in 3–5 % of the cases [96]. There is also a higher incidence of other malignant tumors, such as gliomas and ovarian and pancreatic tumors. A long-term follow-up is therefore mandatory [93].

16.6.6 Parkes Weber Syndrome

Parkes Weber syndrome combines a cutaneous capillary malformation with limb hemihypertrophy, congenital varicose veins, and arteriovenous malformations (a major difference with Klippel-Trenaunay syndrome). Numerous small periarticular arteriovenous fistulas or shunts can be detected in the affected limb [97]. Cardiac failure occurs in some patients with high blood flow vascular malformations.

16.6.7 Rendu-Osler-Weber Syndrome

Hereditary hemorrhagic telangiectasia (Rendu-Osler-Weber syndrome) is a genetic, autosomal dominant disorder. It is characterized by telangiectasia and arteriovenous malformations in specific locations, leading to epistaxis and hemorrhage into the digestive tract [98]. Lesions commonly involve the mucous membranes, skin, lungs, and genitourinary and gastrointestinal systems. At imaging, Rendu-Osler-Weber syndrome is characterized by arteriovenous malformations or fistulas in the lungs, liver, central nervous system, or other sites [99].