Lump on the scalp of a child arising over a previous parietal fracture: growing skull fracture or post-traumatic lipoma?

Abstract

A young girl was referred to our Institution for the appearance of a painless soft swelling in the right parietal region of the scalp. In the same site, the patient had a parietal bone fracture 1 year ago. In the suspicion of a growing skull fracture, the patient underwent radiological investigations. Ultrasound showed a soft, poorly vascularised swelling with parenchymatous content. The skull X-ray showed an apparent healing of the previous fracture. CT scan and MRI confirmed the correct healing of the fracture and described the presence of a lipomatous mass. The mass was surgically removed and histology confirmed the diagnosis of encapsulated lipoma. The postoperative period was uneventful, with no evidence of infections or recurrence in the 6-month follow-up.

Background

Lipomas are benign, slow-growing mesenchymal tumours composed of mature adipocytes encapsulated by a thin layer of fibrous tissue and they are generally excised with no complications or reoccurrence. Although lipomas have been described in almost any part of the body, they are relatively uncommon in the head and neck region, especially on the scalp, due to the intrinsic anatomy of this area, with a prevalence of 2%–14%.¹ It has been reported that lipoma can arise after a blunt trauma. These ‘post-traumatic lipomas’ might develop as the result of rupture of the fibrous septa and anchorage connections between the skin and deep fascia, resulting in a proliferation of adipose tissue.² Local inflammation secondary to trauma may also be a reason for preadipocytes differentiation and maturation.³

When dealing with post-traumatic swelling on the scalp of children, an important differential diagnosis is the growing skull fracture (GSF), a rare complication of paediatric skull fractures, with an incidence of about 1%.⁴ GSF is due to the presence of a tear of the dura mater associated with a non-consolidating cranial fracture, with consequent herniation of the meninges and/or the cerebral parenchyma.⁵ A prompt diagnosis of GSF is essential, as delay in management can lead to progression of the disease. Three factors are considered to be necessary conditions for the formation of GSF: a cranial bone fracture, underlying dural tear, and intracranial expansile force.⁶ For these reasons GSF is most commonly seen below 3 years of age because of the rapid growth of the brain at that age.⁷ The treatment of GSF is surgical, although there is still a debate both as regards the technique to be adopted and the timing of the procedure.³ The difficulties are related to an adequate reconstruction of the dural tear combined with the possibility of a bone graft, without however limiting the growth of the brain and skull.⁶

The differential diagnosis of post-traumatic lipoma and GSF requires an accurate radiological workup, as they can be clinically indistinguishable. CT scan is the most useful exam to rule out a GSF, as it shows the diastatic fracture and brain herniation, and MRI is mandatory to confirm the diagnosis and to visualise more accurately the extent of the dural defect.⁶

We report the case of a young girl who developed a post-traumatic lump 1 year after trauma, for which the patient underwent complete radiological investigations and surgical removal of the mass, which was ultimately diagnosed as encapsulated lipoma.

Case presentation

A young girl was referred to our hospital for a lump in the right parietal area of the scalp, grown in 1 year after a right parietal fracture (figure 1) secondary to a domestic fallen. The mass was painless and soft, fixed on the deep plane, and measured 40×40 mm. The scalp above it appeared intact. During the previous year the patient did not have any neurological symptoms.

Figure 1.

The X-ray of the previous right parietal skull fracture occurring in the same site of the current lump.

Investigations

The patient underwent first an ultrasound, which documented the presence of a solid, poorly vascularised swelling of the scalp, semispheric in shape, located in the subgaleal plane (figure 2). The cranial X-ray (figure 3) showed an apparent good healing of the previous fracture (figure 1), which was confirmed by the three-dimensional CT scan (figure 4). A well-circumscribed semispherical mass on the right parietal area, quite homogeneous, with no calcifications was also showed by the CT scan (figures 5 and 6). The lump on MRI appeared as a soft subgaleal mass with a poorly vascularised lipomatous content, measuring 40×38 mm, with a high signal on T1-weighted and T2-weighted sequences and a suppressed signal on fat-saturated sequences (figures 7 and 8).

Figure 2.

Ultrasound documented the presence of a solid, poorly vascularised, subgaleal swelling of the scalp with a semispheric shape. The galea aponeurosis appeared as a fine linear hypoechoic structure between the mass and the subcutaneous fat.

Figure 3.

The actual cranial X-ray showed a good healing of the previous parietal fracture.

Figure 4.

3D CT scan showing the correct healing of the previous right parietal fracture. 3D, three dimensions.

Figure 5.

Assial CT scan showing the right parietal lump.

Figure 6.

Coronal CT scan showing the right parietal lump.

Figure 7.

MRI T1-weighted sequences.

Figure 8.

MRI T2-weighted sequences.

Differential diagnosis

Due to the history of a previous fracture in the same site, the first hypothesis was a GSF. The patient was neurologically asymptomatic and the palpable mass was non-pulsating, a condition sometimes present in GSF but not pathognomonic for it. The CT scan showed a complete healing of the previous parietal fracture, ruling out the hypothesis of a GFS. Since the majority of scalp lesions are benign, other possible differential diagnoses included benign tumours, both cystic, (ie, trichilemmal cysts/pilar cysts, sebaceoma, epidermoid cysts, dermoid cysts and teratoid cysts), which account for over 50% of all benign scalp lesions, and solid, including melanocytic nevi, keratoacanthoma, pilomatricoma, neurofibroma and lipoma with its variants, such as spindle cell lipomas and hibernomas.⁸ In paediatric populations, 97%–99% of all scalp lesions are benign, with the most common diagnosis being nevus sebaceous (60% of all scalp lesions), followed by infantile haemangioma, melanocytic nevi and juvenile xanthogranuloma.⁹ In our case, the slow growth of the lesion, its radiological patterns on ultrasound and MRI and the history of previous trauma in the same region oriented the diagnosis towards a post-traumatic lipoma.

Treatment

After injection of 2% lidocaine containing 1:10 000 norepinephrine, the subgaleal mass was surgically dissected and completely removed, with preservation of the periosteum. Macroscopically, the lesion was yellowish, encapsulated, and measured 40×38 mm (figures 9–11). The previous parietal fracture was no longer visible. Adequate haemostasis and suture of tissue planes completed the surgery (figure 12). A compression dressing was applied on the surgical wound to prevent postoperative swelling. Histology confirmed the diagnosis of encapsulated lipoma.

Figure 9.

The surgical aspect of the lump.

Figure 10.

The aspect of the lipoma after excision.

Figure 11.

The galea aponeurotic defect and the periosteum left intact under the lesion.

Figure 12.

Final scalp suture.

Outcome and follow-up

The postoperative course was uneventful. The child was discharged fit and well the day after surgery with a compressive dressing, removed 7 days after the procedure. She did not develop any wound infections and did not complain any pain during the following days. At the 6-month follow-up the patient showed no signs of recurrence. The wound showed good healing, with no signs of alopecia or excess skin.

Discussion

Lipomas are common benign tumours that can arise in any part of the body but are rarely encountered on the scalp. Post-traumatic encapsulated lipomas are very uncommon, especially in children. Most reported cases of post-traumatic lipomas are located at the abdomen, face, and lower extremities. Aust et al collected 31 cases of post-traumatic lipomas, arising in adult patients with a mean age of 52 years (range 18–74 years).¹⁰ In this series, which is the most numerous in the literature, only 2 out of 31 patients presented a localisation at the level of the scalp, with a predilection for the forehead. To the best of our knowledge, this is the first case of a post-traumatic lipoma arising on the scalp of a paediatric patient after a skull fracture. The existence of a pathogenic link between blunt soft tissue trauma and the formation of post-traumatic lipomas is still controversial. Two potential mechanisms may explain this event: first, the formation of so-called post-traumatic ‘pseudolipomas’ may result from a prolapse of adipose tissue through fascia induced by direct impact. Alternatively, lipoma formation may be a result of preadipocyte differentiation and proliferation mediated by cytokine release following soft tissue damage after blunt trauma and haematoma formation.¹¹

From the radiological point of view, ultrasonography is particularly accurate for the detection of lipoma on the scalp.¹² Usually, it presents as a well-defined, semispherical, echogenic mass with striated echoes under the hyperechoic fascial layer, which are the same findings observed in our case (figure 2). In doubtful cases, the use CT scan and MRI has been shown to be useful, especially for the differential diagnosis with GSF in paediatric patients, as they can be clinically difficult to differentiate.¹³

As regards the treatment, post-traumatic lipomas can be removed by surgical excision, liposuction or laser extirpation.¹⁴ Liposuction and laser extirpation have the advantage of being less invasive but are burdened by an increased risk of recurrence and do not provide information on the histological nature of the lesion.¹⁵ In our case, we opted for surgical removal: the strategy was chosen for the favourable location of the lipoma, scarce morbidity and absence of visible scars. In addition, the surgical removal allowed a definitive histological diagnosis and the radicality of the procedure reduced the possibility of recurrence. Further clinical and experimental studies should be carried out to understand the pathogenesis of post-traumatic lipomas of the scalp, especially in the infant population.

Learning points.

• In case of a lump arising over a previous fracture in children, growing skull fracture (GSF) needs to be promptly ruled out to avoid neurological sequelae.

• Although uncommon, especially in children, post-traumatic lipoma should be considered in the differential diagnosis of a post-traumatic lump on the scalp.

• CT scan and MRI are the best exams to differentiate post-traumatic lipoma and GSF.

• Lipoma of the scalp presents as a well-defined, semispherical, echogenic mass with striated echoes under the hyperechoic fascial layer at the ultrasound exam.

• Due to the favourable site, scalp lipoma should be treated by surgical excision.

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