Contents



26.Imaging of Soft Tissue Tumors in The Pediatric Patient

L Jans, K Verstraete

Contents

26.1 Introduction

26.2 Role of Imaging

26.3 Imaging Modalities

27.3.1 Ultrasound

27.3.2 Plain film/CT

27.3.3 MR Imaging

26.4 Role of Imaging in Tissue Characterization

References

26.1 Introduction

Pediatric soft tissue tumors are rare. About 5% of soft tissue tumors arise in utero and in young children (0–5 years) and only 7% in children between 6 and 15 years old [1, 2].

About 79% of soft tissue tumors in children between 0 to 5 years old are benign, as are 70% in those from 6 to 15 years [3].

Some tumors are more frequently encountered in the pediatric age group [4-25]. Most common malignant tumors in children between 0 and 5 years are fibrosarcoma (36% of malignant soft tissue tumors in this age group), rhabdomyosarcoma (21%), giant cell fibroblastoma (7%), dermatofibrosarcoma protuberans (6%), angiomatoid malignant fibrous histiocytoma (5%) and malignant peripheral nerve sheath tumor (5%). In children between 6 and 15 years, the most common malignant tumors are angiomatoid fibrous histiocytoma (16%), synovial sarcoma (13%), rhabdomyosarcoma (11%), fibrosarcoma (8%) and malignant fibrous histiocytoma (7%) [1,2].

The Kiel Pediatric Tumor Registry (n=4272 soft tissue malignancies) found rhabdomyosarcoma to be the most frequent sarcoma (44.6%), followed by Ewing tumors (22.3%), malignant peripheral nerve sheath tumors (8.1%), synovial sarcomas (5.0%), leiomyosarcomas (3.2%), fibrosarcomas (2.4%), extrarenal malignant rhabdoid tumors (2%), and alveolar soft tissue sarcomas (1.1%). A further group (11.3%) includes rare tumors, intermediate fibrohistiocytic tumors, and unclassified sarcomas [15]. Embryonal rhabdomyosarcomas are 2.5 times more frequent than alveolar rhabdomyosarcomas, which are prognostically unfavorable and located predominantly in the extremities and the trunk. With regard to clinical findings, histology, molecular biology and prognosis, embryonal and alveolar rhabdomyosarcomas have to be considered as two different tumor types. The family of Ewing tumors includes extraosseous Ewing’s sarcoma and primitive neuroectodermal tumors, the former tumors without and the latter with neural differentiation. Many cases of infantile malignant peripheral nerve sheath tumors and infantile fibrosarcomas are low-grade malignancies and are prognostically more favorable than in adults [26].

The most common benign masses in young children between birth and 5 years are hemangioma (15% of all benign tumors in this age group), fibromatosis (11%), granuloma annulare (10%), infantile myofibromatosis (8%), and lipoblastoma (8%). The most frequent benign tumors in older children (6 to 15 years) are fibrous histiocytoma (17%), nodular fasciitis (16%), hemangioma (13%), and fibromatosis (5%) [1,2] (Table 26.1). Imaging findings of common pediatric soft tissue tumors are illustrated in Fig.1-7.

Location In children younger than 6 years of age 60% of benign and malignant lesions occur in the head and neck region, the lower extremity or the trunk. In children of 6 to 15 years old benign tumors often occur in the hand or wrist, the head and neck region and the lower extremities [1,2], whereas malignant soft tissue tumors are more common in the extremities or the trunk. Many of the primary sites of childhood rhabdomyosarcoma, such as the orbit, bladder, prostate, and paratesticular region are rarely primary sites of the non-rhabdomyosarcoma tumors in children and of other soft tissue sarcomas in adults [1,2].

26.2 The Role of Imaging

Benign masses with characteristic clinical presentation may be recognized by experienced clinicians and may not require imaging. Most cutaneous or subcutaneous masses are small and often excised without imaging.

Children frequently have nonspecific symptoms and complaints are often initially neglected or diagnosis may be delayed. As children often have injuries related to play, pain and soft tissue masses may be attributed to trauma. Therapeutic options and long-term survival of soft tissue tumors is strongly related to the disease stage at the time of diagnosis. This stresses the importance of performing timely and dedicated imaging studies.

Current methods of diagnosis such as dynamic contrast-enhanced MR imaging, PET scan, molecular biology, immunology and cytogenetics give additional insight into the biology of tumors and may help us in tailoring therapeutic strategies according to these biologic and imaging characteristics.

Tables present the most common locations for tumors (Table 26.1), multiplicity (Table 26.2), different shapes associated with specific soft tissue tumors (Table 26.3), and specific MR features, including presence of signal voids (Table 26.4) and fluid-fluid levels (Table 26.5) [4-25].

Table 26.1. Preferential location of soft tissue tumors

|Location |Tumor |

|Neck |Cystic hygroma – lymphangioma |

|Sternocleidomastoid muscle |Capillary hemangioma |

| |Fibromatosis colli |

|Trunk |Askin (PNET) tumor |

|Axilla |Cystic hygroma-lymphangioma |

|Upper limb | |

|Wrist |Ganglion cyst |

|Wrist, volar aspect |Fibrolipohamartoma of median nerve |

|Hand, volar aspect |Fibrolipohamartoma of median nerve |

|Finger, dorsal aspect |Digital fibroma |

|Lower limb | |

|Thigh |Fibrohamartoma of infancy |

|Knee |Synovial hemangioma |

|Knee, tibiofibular joint |Ganglion cyst |

|Ankle |Ganglion cyst |

|Foot, extensor aspect |Ganglion cyst |

|Upper and lower limbs |Myositis ossificans |

|Hand and feet |Calcifying aponeurotic fibroma |

|Joints, periarticular |Synovial hemangioma |

|Cutis, subcutis |Dermatofibrosarcoma protuberans |

Table 26.2. Multiplicity

|Venous malformation |

|Lipoma (5–8%) |

|Neurofibroma |

|Dermatofibrosarcoma protuberans |

|Desmoid |

Table 26.3. Shape

|Fusiform (ovoid) |Neurofibroma |

| |Lipoma |

|Dumbbell |Neurofibroma |

|Moniliform |Neurofibroma |

|Round |Cyst |

| |Schwannoma |

|Serpiginous |Hemangioma |

| |Lymphangioma |

Table 26.4. Intratumoral signal void

|Flow |Hemangioma (capillary) |

| |Arteriovenous malformation |

|Calcification |Hemangioma (phlebolith) |

| |Lipoma (well-differentiated and dedifferentiated) |

| |Myositis ossificans (marginal) |

| |Myofibromatosis |

Table 26.5. Fluid-fluid levels

|Hemangioma |

|Cystic lymphangioma |

|Synoviosarcoma |

|Hematoma |

26.3 Imaging Modalities

26.3.1 Ultrasound

The value of ultrasound is limited. In a study by Brouns et al. [27] about delay in diagnosis of soft tissue sarcoma, wrong diagnosis on ultrasound was the most frequent reason for this delay.

Ultrasound demonstrates the shape, volume, borders and compressibility of small masses and the relationships to adjacent structures and allows to differentiate solid from cystic lesions.

Dynamic US examination of a soft tissue mass (e.g. flexion or extension maneuvers) allows to evaluate the relationship of the lesion to the underlying fascia, muscles or tendons. Deeper seated or larger tumors are more difficult to examine adequately because anatomic landmarks are lacking and depth penetration is limited. To achieve deeper penetration and a wider field of view, transducers with lower frequency (5 MHz) are useful but result in a lower the spatial resolution.

However, since there are no pathognomonic ultrasound criteria for grading soft tissue tumors, ultrasound often does not allow to differentiate between benign and malignant soft tissue masses. The specificity of ultrasound is low, resulting in the inability to give an accurate tissue-related diagnosis.

Some soft tissue masses with a characteristic shape and/or echogenicity include neurogenic tumors (oval, hyporeflective masses often with posterior acoustic enhancement), lipomas (oval, mostly well-circumscribed, homogeneous masses), ganglion cysts (anechoic and rounded), hemangiomas (irregular, slightly hyperreflective lesions, often with echogenic phleboliths with posterior acoustic shadowing), and lymphangiomas (polylobular, poorly defined with cystic and solid components and septa) [28,29].

Color Doppler helps quantify the degree of vascularization and analysis of flow patterns and is useful in diagnosing tumor vascularity (as occurs in hemangiomas), evaluates response to chemotherapy and guides biopsy [28].

Ultrasound may also be useful in detecting retained foreign bodies in patients with a pseudotumoral inflammatory mass, and in diagnosing a ganglion cyst, bursitis, or abscess.

26.3.2 Plain Film/ CT

Plain films are of limited value in workup of a pediatric soft tissue mass. Involvement of adjacent osseous structures may be detected (e.g. in myofibromatosis, juvenile hyaline fibromatosis, infantile fibrosarcoma, and angiomatosis). Associated bone alterations may be visible (e.g. macrodactyly in fibrolipohamartoma) and the presence and morphology of intralesional calcifications (e.g. hemangiomas, myofibromatosis) or ossifications may be evaluated and lead to a correct diagnosis. Plain films may also identify pseudotumoral lesions (e.g. myositis ossificans).

CT examination shows involvement of the adjacent bony structures more accurately than on plain films and intralesional calcifications, fat, fluid, vessels, blood, and gas may be adequately recognized on CT. However, MR imaging is the first choice cross sectional imaging technique for evaluation soft tissue tumors.

26.3.3 MR Imaging

MR imaging is the key modality for imaging soft tissue tumors in children.

Fat-saturated (FS) T1- and T2-weighted sequences are typically obtained. Gadolinium-enhanced T1-weighted images help to define the local tumor extent, demonstrate intratumoral necrosis and plays a role in follow-up [30,31]. Dynamic contrast-enhanced MR imaging is useful for assessment of tumor vascularization and therapy follow-up [31].

26.4 Role of Imaging Tissue Characterization

Characterization of a tumor consists of both grading and the tissue-specific diagnosis [32].

Although histology is the gold standard, prediction of a histological diagnosis remains one of the goals of imaging. If imaging studies could provide a specific diagnosis or a limited differential diagnosis, decisions on biopsy and treatment could be simplified.

MR tissue characterization is limited for two reasons. First of all, MR images provide indirect information about tumor histology by showing signal intensities related to some physicochemical properties of tumor components (e.g. fat, blood, water, collagen) and, consequently, reflect gross morphology of the lesion rather than underlying histology. Soft tissue tumors belonging to the same histologic group may have a different composition or different proportions of tumor components resulting in different MR signals; this feature is well exemplified by the group of lipomatous tumors. Only lipomas and well-differentiated liposarcomas are predominantly fatty, while lipoblastomas have less than 25% fat.

The second difficulty in obtaining a tissue-specific diagnosis on soft tissue tumors on MR imaging is related to the time-dependent changes that occur during natural evolution or as a consequence of therapy. Young fibrous tumors are highly cellular, with a high water content that results in high SI on T2-WI. As they become more collagenous and less cellular, a decrease in SI is seen which is more characteristic of fibrous tissue. Another example of time-related changes is the signal intensity of malignant tumors that undergo changes as a consequence of intratumoral necrosis or hemorrhage.

The highest confidence in characterization is seen in benign masses such as lipomas, hemangiomas, benign neurogenic tumors, periarticular cysts, hematomas and abscesses. Laor and Burrows reported on the ability of MR imaging to differentiate between different subtypes of hemangiomas [33]. A mass lesion with MR signal in keeping with high flow most often corresponds to an infantile capillary hemangioma, whereas a high flow pattern without obvious mass represents an arteriovenous hemangioma. A mass lesion with slow flow MR signal corresponds to a venous hemangioma or a lymphangioma. Slow flow diffusely enhancing lesions correspond to venous hemangiomas, whereas septal enhancement is seen in lymphangiomas [33].

The imaging parameters for predicting the malignancy of soft tissue tumors in adults and children have been discussed by several groups [34-36] and include size, shape, margin, homogeneity of signal intensity on different sequences, contrast enhancement on both static and dynamic studies, peritumoral edema, hemorrhage/necrosis, growth rate, and extent (intra- or extra-compartmental, bone involvement and neurovascular displacement/encasement) (see chapter 10) Few studies have been published on differentiation between benign and malignant soft tissue tumors in children. One must always approach an apparently benign, small, well-circumscribed tumor carefully, and masses should be considered to be indeterminate unless the tissue-specific diagnosis can be given with reference to the child’s age, signal features and location.

Key messages:

1. Soft tissue tumors are rare in childhood and adolescence. They are mostly benign. Hemangiomas are the most common benign, rhabdomyosarcomas the most common malignant soft tissue tumors.

2. Despite its limitations, ultrasound remains a valuable diagnostic modality in children suspected of having a soft tissue tumor.

3. Plain film and CT demonstrate calcified lesions or intralesional calcifications.

4. MR imaging is the first choice modality of grading, staging and characterizing pediatric soft tissue tumors.

5. As long term survival of children with malignant soft tissue tumors is strongly related to disease stage at the time of diagnosis, early detection is mandatory.

6. Tissue specific diagnosis by imaging is achievable in a the majority of benign tumors but is notoriously difficult in malignant tumors.

7. Children with a soft tissue tumor should be referred to specialized centers for diagnosis, treatment and follow-up.

Figures

Fig. 1: Fibromatosis colli in 6-week-old boy.

a) Ultrasound shows a heteroechoic thickening of the central part of the sternocleidomastoid muscle.

(b-d) Axial and Sagittal T2-weighted MR images show a hypointense focal thickening (long arrows) of the right sternocleidomastoid muscle. The left sternocleidomastoid muscle (short arrow) is normal.

[pic] [pic]

[pic] [pic]

Fig. 2: Granuloma annulare in a 3-year-old girl.

(a-b) Axial T1-weighted images show a subcutaneous soft tissue lesion (arrows) enhancing after contrast administration.

(c) Coronal fat-saturated (FS) T2-weighted MR image shows multiple ill-defined hyperintense lesions (arrows).

[pic] [pic] [pic]

Fig. 3: Fibrosarcoma in a 1-year-old girl.

(a-b) Coronal T1 and T2-weighted MR images show a large soft tissue mass in the right axilla.

b) Axial CE FS T1-weighted image depicts intense homogeneous enhancement of the lesion.

[pic] [pic] [pic]

Fig. 4: Synovial sarcoma in a 16-year-old-girl.

Axial (a) FS T2 and (b) CE FS T1-weighted MR images show a heterogeneous, partially enhancing mass in the soft tissues anterior of the shoulder.

[pic] [pic]

Fig. 5: Infantile rhabdomyosarcoma in a 1-day-old girl.

(a-b) Axial and sagittal FS T2-weighted images show multiple soft tissue lesions (arrows) with cystic and solid components anterior to the nose and in the submandibular space.

c) Sagittal CE FST1-weighted image shows enhancement of the solid components of the mass.

[pic] [pic] [pic]

Fig. 6: Infantile haemangioma in a 4-year-old boy.

(a-b) Sagittal and coronal FS T2-weighted images show a soft tissue mass with flow voids (arrows) due to presence of vessels with high flow.

c Sagittal CE T1-weighted image shows intense homogeneous enhancement of the mass.

[pic] [pic] [pic]

Fig. 7: Infantile haemangioma in a 4-year-old boy.

(a) Coronal FS T2-weighted image shows a soft tissue mass on the right side of the neck.

(b) Axial CE T1-weighted image shows marked homogeneous enhancement of the mass.

[pic] [pic]

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Figures

Fig. 1 Haemangioma

060721 002A57 MRI

Fig. 2 Fibromatosis

130419 008A43 MRI

130213 003A20 Echo

Fig. 3 Granuloma annulare

080511 011a85 MRI

Fig. 4 Rhabdomyosarcoma (0-5 year old)

110524 002a58 MRI

Fig. 5 Fibrosarcoma

070706 011A34 MRI

Fig. 6 Rhabdomyosarcoma (6-16 year old)

010717 010A64 MRI

Fig. 7 Ewing’s

Fig. 8 Synoviosarcoma

870811 040A58 MRI

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