In the presence of a lump in the head of a child,
first of all,
we should try to narrow the differential diagnosis with relevant clinical data,
such as whether the lesion was present at birth or not,
if there is a history of trauma,
if it is stable or growing.
Unfortunately,
in the majority of cases,
the clinical history is confusing and unspecific.
Imaging techniques:
Radiographic images are usually unspecific and only lesions with bone involvement can be demonstrated.
B-mode and color Doppler ultrasound (US) are the first-line imaging modalities of choice,
due to its wide availability and lack of radiation.
As these lesions are located superficially,
they can be easily evaluated with US,
using a linear probe.
US provides rapid information about size,
contents (solid or cystic),
vascularity,
location: skin,
subcutaneous tissue or bone (Fig. 1) and relationship with adjacent structures [1].
In some cases,
the US and radiographic appearance can be diagnostic.
If the mass is large,
deep or has features of malignancy,
further evaluation is required.
In the case of lytic lesions,
CT may be useful to evaluate bone destruction and tumor spread.
However,
it has two main disadvantages,
which are the use of radiation and that it offers a poor detail in the evaluation of soft-tissues.
On the other hand,
MR imaging offers excellent soft-tissue contrast,
anatomic and vascularization details and it's also useful in evaluating intracranial connection of small lesions [2].
Unfortunately,
the lesser availability of MRI and the necessity of sedation might limit the use of this technique.
Differential diagnosis of pediatric head lumps:
To review and analyze the wide group of entities that can be presented as a head lump,
we will divide them into congenital,
benign and malignant lesions.
1.
CONGENITAL LESIONS
- Dermoid and epidermoid cysts
Both lesions may overlap in imaging.
Radiological features may vary depending on the content.
Dermoids are unilocular cysts that typically contain thick greasy sebaceous material,
keratin debris and skin adnexa such as hair follicles.
Epidermoid cysts are inclusion cyst with keratin and cholesterol without skin elements.
Sinus tracts reaching the skin surface can be seen in the nasal area.
Dermoids and epidermoids cannot be distinguished from each other with US [1].
In both cases,
US typically demonstrates a well-defined hypoechoic and avascular mass with posterior acoustic enhancement shadow and bone scalloping.
They may contain echogenic foci from the presence of calcification,
fat or proteinaceous material [4,5].
On radiography,
both dermoid and epidermoid cysts might appear as lucent lesions with well-defined sclerotic margins Fig. 2.
MRI is not indicated unless there is a suspicion of intracranial extension or when the diagnosis is uncertain.
On MRI,
as a general rule,
a cystic mass with lipids that has no contact with intracranial structures,
suggests a dermoid cyst [5].
Epidermoids typically,
but not specifically,
has a restricted signal on diffusion-weighted images Fig. 3.
If the intracranial connection is seen,
the diagnosis of an encephalocele should be considered.
- Encephalocele
It is a herniation of intracranial tissue through a defect in the cranium and it is often associated with other intracranial malformations Fig.
4,
Fig. 5.
In the presence of a midline nasofrontal mass,
MRI is useful in differentiating a dermoid cyst from a frontoethmoidal encephalocele or nasal glioma, which is a congenital benign lesion composed of dysplastic heterotopic glial tissue,
with signal intensity similar to the brain,
not communicated with the subarachnoid spaces.
- Vascular
Vascular anomalies of the head and neck region constitute approximately 60% of vascular anomalies diagnosed in children.
Vascular lesions are divided into two categories,
vascular tumors,
and vascular malformations.
The physician should exclude features of a vascular lesion with associated syndromes [6].
- Infantile hemangiomas are the most frequent vascular tumors,
and they usually appear during the first year of life and resolve spontaneously.
Congenital hemangiomas,
in contrast,
are rare and they are fully formed at birth.
Classic history and presentation can help to differentiate them from other vascular lesions. During the proliferative phase,
US shows a solid mass with heterogenic echogenicity and numerous venous and arterial vessels inside [7,8,9].
On MRI,
the lesion appears as well-circumscribed lobulated lesion hypo- to isointense relative to muscle on T1-weighted images,
and hyperintense on T2-weighted images,
with an early and intense enhancement after contrast material administration Fig. 6 Fig. 7
- Vascular malformations are present at birth and grow with the child.
They may undergo phases of accelerated growth during puberty. Spontaneous involution does not occur.
They can be divided into low-flow (lymphatic,
venous,
capillary or mixed) or high-flow malformations (arteriovenous malformations and fistulas).
- On ultrasound,
lymphatic malformations appear as multiseptate cystic masses whether venous or mixed malformations are ill-defined heterogeneous lesions with anechoic areas which may present hyperechoic foci from bleeding or thrombosis or calcifications (phleboliths).
- Venous or mixed malformations are usually visualized on MRI as a lobulated multilocular mass (venous lakes separated by septa).
It shows intermediate signal intensity in T1 images and hyperintense in T2,
with signal voids secondary to phleboliths and heterogeneous enhancement due to the presence of thrombi.
[6,7,8,9] Fig. 8
- Lymphatic malformations will show a non-enhancing,
thin-walled,
uni- or multi-loculated cystic lesion with septal enhancement [6] Fig. 9.
- Arteriovenous malformations (AVM) are rare lesions in which arterial and venous systems are connected directly by a nidus.
On US,
AVM appears,
in general terms,
as a conglomerate of tortuous vessels without a well-defined mass.
Doppler US can show an arteriovenous shunt,
with high velocities and low resistance flow in the arteries.
MRI typically demonstrates an ill-defined soft tissue mass with flow voids and early arterial enhancement.
MRI is also useful to assess intracranial involvement [6] Fig. 10.
- Another congenital lesion that rarely appears as a palpable lump is the arachnoid cyst. It is a benign and asymptomatic lesion,
usually located within the subarachnoid space which contains CSF.
The majority of arachnoid cysts are supratentorial.
On imaging studies, they appear as well-circumscribed cysts. They typically displace structures nearby and can remodel the bone Fig. 11.
2.
BENIGN LESIONS
- Lymph nodes
Because children have hypertrophic lymphatic tissue and little fat in the craniocervical area,
it is very common to find palpable lymph nodes in this age group and location.
Therefore,
lymph nodes constitute a common reason for parents concern and ultrasound evaluation.
The evidence of a nodular soft tissue mass with central echogenic vascular hilum is normally enough for characterization (Fig. 12).
Only when they are bigger than 1cm or heterogeneous further studies should be carried out.
- Langerhans cell histiocytosis (LCH)
LCH is a proliferation of pathologic Langerhans cells.
It can be classified into three groups,
depending on how many sites and organs are affected.
Localized LCH is the most common form,
and most-frequently involves the bone in children.
The calvaria is the most common location of osseous LCH,
followed by the orbit,
maxilla,
mandible and temporal bone.
It is more common in children between 1-4 years of age.
On radiography,
bone LCH appears typically as lytic lesions without periosteal reaction or reactive changes ("punched out" lesions).
On US,
it appears as a solid mass extending from the diploic surface,
with poor vascularity.
CT and MRI can demonstrate a soft-tissue mass with bone destruction.
On MRI this lesion shows intermediate signal intensity on T1-weighted images and high signal on T2-weighted images.
Diffuse and mild enhancement can be shown.
MRI can better demonstrate intracranial extension [11] Fig. 13, Fig. 14.
-Other lesions
The pilomatricoma or pilomatrixoma,
which arises from the hair matrix,
is a common benign lesion in children.
Up to 68% of pilomatricomas are found on head and neck.
They are small subcutaneous lesions that frequently calcify.
On US,
a pilomatricoma appears as a small and well-circumscribed soft-tissue mass that may contain echoic foci from the presence of calcification (Fig. 15).
On MRI it is iso or hypointense in all MRI sequences,
with a patchy or peripheral enhancement.
Peritumoral edema or inflammation can be seen at MRI imaging in pilomatricomas,
emulating other more agressive pathologies [12] (Fig. 16).
- Subcutaneous granuloma annulare
It is an uncommon and idiopathic benign inflammatory condition most commonly seen in kids aged 2-5 years.
It can affect the scalp,
usually the occiput.
US shows a solid,
poorly-defined,
hypoechoic,
fascial based mass.
On MRI,
an ill-defined lesion can be seen,
iso-intense to muscle on T1-weighted images and heterogeneous hyperintense on T2-weighted images with fascial tail and variable enhancement [9] (Fig. 17).
Myofibromatosis (multicentric) or myofibromas (solitary) are the most common fibrous tumors in infancy,
mainly in children under 2 years. Myofibromas are benign tumors characterized in imaging by presenting a low signal at T1 and variable at T2-weighted images,
with peripheral enhancement after administration of intravenous gadolinium ("target" sign) [12,13] (Fig. 18)
- Angiomatoid Fibrous Histiocytoma
Angiomatoid Fibrous Histiocytoma is a rare low-grade soft-tissue tumor with origin in dermis a subcutaneous tissue.
It is most commonly seen in children and young adults. It has slow growth and sometimes it can simulate a bruise.
Although it is not specific,
on imaging this tumor can appear as a multicystic mass with internal fluid-fluid levels that indicate intralesional hemorrhage and enhancing solid parts.
It also may be calcified.
[14] (Fig. 19).
3.
MALIGNANT LESIONS
-Sarcomas
Soft tissue sarcomas account for 4-8% of cancers in patients up to 14 years of age.
35% of all sarcomas in the pediatric population manifest in the head and neck.
Rhabdomyosarcoma is the most soft-tissue sarcoma in children [2].
In the head and neck,
it is classified as orbital,
parameningeal or superficial.
Clinically,
they can mimic other soft-tissue lesions or even an infection.
At imaging,
they appear as a poorly defined mass,
isointense on T1-weighted images and hyperintense on T2-weighted images,
with bone destruction and moderate enhancement (Fig. 20).
-Osteosarcoma and Ewing sarcoma
Malignant tumors of the skull are unusual,
but osteogenic sarcoma and Ewing sarcoma have been reported (Fig. 21).
-Metastatic Lesions
Metastatic lesions of the calvarium in children include leukemia,
neuroblastoma,
and small round cell tumors.
Neuroblastoma commonly metastasizes to the lateral orbital walls,
skull base,
and calvaria Fig. 22, Fig. 23.
4.
TRAUMATIC LESIONS
A variety of traumatic lesions can occur during the neonatal period due to delivery (:
-Caput succedaneum
Diffuse swelling of the scalp that contains fluid and blood.
Medical support is not required.
-Subgaleatic hematoma
It consists on hemorrhage located subjacent to the aponeurosis covering the scalp.
It also crosses sutures lines.
It can appear up to 4 days postpartum.
In order to assess potential intracranial injuries,
cranial US should be performed.
-Cephalohaematoma
This is a blood collection between the periosteum and the skull.
It does not cross sutures.
Associated fractures may be found.
Cephalohaematomas can mimic epidural hematomas (mirrow artifact).
Color Doppler ultrasound is helpful by showing normal vessels within the suspicious epidural hematoma [15].
Chronic cephalhaematomas may calcify.
(Fig. 25),
(Fig. 26),
(Fig. 27).
- Ping-pong fracture:
A ping-pong fracture is a depressed skull fracture without loss of bony continuity.
It can appear in newborns,
after a localized skull compression (maternal pelvis,
forceps..)[15].
In the physical examination,
the non-depressed part of the skull may be confused with a head bump (Fig. 28).