Self-limiting sternal tumour of the childhood - An important diagnosis not to be missed

Clinical History

A 22-month-old boy came to the emergency department due to recent appearance of a non-painful two-centimetre lump in the pre-sternal region. The patient had no history of trauma nor other associated symptoms. The child was afebrile and in a good clinical condition. Laboratory findings were unremarkable.

Imaging Findings

At physical examination the mass was of soft tissue consistency, non-mobile and slightly red but without other inflammatory signs (Fig. 1).
Auxiliary diagnostic tests performed were thoracic X-ray with lateral view and soft tissue ultrasound; the thoracic X-ray showed a discrete soft tissue densification in the sternal region without bone involvement (Fig. 2) and the ultrasound revealed an hypoechoic lesion with dumbbell appearance at the soft tissues anteriorly to the joint of the body with the xiphoid process of the sternum, without involving muscle or bone (Fig. 3).

Discussion

Primary tumours of the thoracic wall are uncommon, representing 5% of all thoracic tumours, and only 1% of these arises in the sternum [1].
Sudden appearance of a sternal lump in a toddler without history of trauma alerts parents and doctors to the possibility of malignancy. Nevertheless, a benign and sterile entity called SELSTOC (Self-Limiting Sternal Tumour of Childhood) should be remembered since there are several reported cases in the literature of lesions with complete resolution without treatment after a variable period of time (varying between 6 months and 1.5 years [1, 2]).
SELSTOC is an entity of unknown cause occurring in toddlers (mean age of 16 months) [2], with non-aggressive features but with rapid growth.
A systematic review of patient age, clinical history and laboratory and imaging findings are crucial to narrow down the differential diagnosis list and may allow an expectant approach in certain cases, avoiding invasive procedures such as biopsy or even surgery [3].
In the case we presented, the clinical characteristics (toddler without systemic symptoms) and imaging findings (non-vascularised and dumbbell appearance without bone invasion or other signs of aggressivity) were suggestive of a benign pathology and the diagnosis of a self-limiting sternal tumour of the childhood was assumed. Conservative treatment with a short cycle of a non-steroid anti-inflammatory drug (NSAID) [2], close clinical evaluation and serial ultrasound follow-up were carried out (Fig. 4). There was some clinical improvement after two weeks and complete resolution of the findings occurred after several months (Fig. 5).
The differential diagnosis of a chest wall mass in children is wide, and includes benign osseous tumours (such as osteoma osteoid, osteochondroma, fibrous dysplasia, mesenchymal hamartoma and inflammatory pseudotumour), malignant primary osseous tumours (Ewing sarcoma and osteosarcoma), malignant soft-tissue tumours (rhabdomyosarcoma and malignant peripheral nerve sheath tumours), metastasis, infection and trauma [4].
The absence of bone involvement or aggressive signs at diagnostic complementary studies, the absence of laboratory findings suggestive of infection and absence of history of trauma excludes the above diagnoses and allows the clinician to be confident with a watchful waiting approach.
Although the list of differential diagnosis of the lesions of the thoracic wall is extensive [4], in the correct epidemiological, clinical and imaging context, the hypothesis of SELSTOC should be considered.
Ultrasound is enough for diagnosis and follow-up of these lesions, avoiding radiation and invasive procedures such as surgery or biopsies. However, the presence of any aggressive findings should prompt further workup.

Differential Diagnosis List

Final Diagnosis

Self-limiting sternal tumour of the childhood (SELSTOC)

URL:	https://www.eurorad.org/case/14842
DOI:	10.1594/EURORAD/CASE.14842
ISSN:	1563-4086