Fibroblastic connective tissue nevus: Clinicopathological and immunohistochemical study of 14 cases

Giant congenital fibroblastic connective tissue nevus associated with vascular anomalies

We described an unusual combination of fibroblastic connective nevus (FCTN) already present at birth with underlying vascular anomalies. Overall, the lesion appeared as a large purplish-brown mass in the groin region up to the third of the right thigh, with partial spontaneous regression during the first three months of life. The FCTN observed exhibited several unusual characteristics: it was congenital, large in size, and located in the lower limbs. Finally, it represented the first case described in which an FCTN arose in association with vascular anomalies.

Fibroblastic Connective Tissue Nevus Mimicking Lipoma on Ultrasound: Case Report and Brief Review

Fibroblastic connective tissue nevus (FCTN) is a rare, benign, and recently described dermal mesenchymal lesion characterized by CD34-positive spindle cells. We present a case of FCTN on the upper back of a 9-month-old boy who was diagnosed with a benign lipoma by ultrasound.

Plexiform Myofibroblastoma: Clinicopathologic Analysis of 36 Cases of a Distinctive Benign Tumor of Soft Tissue Affecting Mainly Children and Young Adults

The spectrum of benign superficial fibroblastic/myofibroblastic tumors continues to expand and includes entities such as plexiform fibrohistiocytic tumor, dermatomyofibroma and fibroblastic connective tissue nevus. Here, we describe a seemingly distinctive group of lesions which we have labeled "plexiform myofibroblastoma" (PM). PM is a rare superficial mesenchymal tumor of fibroblastic/myofibroblastic lineage that predominantly occurs in children and young adults. Thirty-six cases from the consultation archives of one of the authors have been studied to characterize the clinicopathologic characteristics of PM. 19 patients (53%) were female and 17 were male, with age at presentation ranging from congenital (2 cases) to 50 years of age (median: 9.5 y). Three patients had multiple lesions. Males tended to develop tumors during childhood (median: 2 y; range: congenital-37 y), while in females the age distribution was relatively uniform from childhood through adulthood (median age: 25 y; range: 4 mo to 50 y). Most tumors occurred in truncal locations (25/40), including the back (11), anterolateral chest wall (4), axilla (4), abdominal wall (4), perineum (1) and suprapubic region (1). Other tumor sites were the neck (10/40), occiput (2), lower extremity (2) and breast (1). The average greatest dimension was 2.7±1.7 cm (range: 0.6 to 8 cm). Three male patients, 2 of whom were brothers, presented between 6 months and 1 year of age with multiple lesions variably involving the back, occiput and axillae; these lesions spontaneously regressed after being present for about 2 years, with no evidence of recurrence at a mean follow-up of 11.4±3.2 years. Histologically, PM was composed of plexiform fascicles of fibroblastic/myofibroblastic spindle cells that ramify through the subcutis and reticular dermis. The bland neoplastic cells had indistinct cell borders, palely eosinophilic cytoplasm and ovoid or tapered nuclei. There was no histiocytoid component in any case, and no cases contained osteoclast-like giant cells. Twelve of thirty-four (35%) reviewed cases showed at least focal keloidal hyalinization, 6/34 (18%) contained somewhat fasciitis-like areas and 6/34 (18%) contained focal myxoid stroma. Immunohistochemical studies were positive for SMA (27/32 cases), desmin (9/21) and CD34 (13/24) and negative for β-catenin (0/14) and S-100 (0/22). EMA was weakly positive in 2/15 cases. An FGFR2 M535L tyrosine kinase domain variant of unknown significance was detected in 1/7 sequenced cases, and no somatic alterations, copy number alterations or gene fusions were detected in the other 6. Clinical follow-up data were available for 16/36 patients (44%; median duration: 5.5 y). Although most excisions had positive margins (11/16), only 1 patient developed a local recurrence 4 years after initial excision. No tumors metastasized. PM is a benign tumor with characteristic histology, epidemiology and anatomic site distribution. Because PM rarely recurs, a watchful waiting approach would be reasonable for lesions excised with positive margins.

Hamartomas of skin and soft tissue

Hamartomas are benign lesions composed of aberrant disorganized growth of mature tissues. Choristomas are similar, except that they are composed of tissues not normally found at the anatomic site in which the lesion is arising. A wide range of hamartomas and choristomas can arise in the skin and soft tissue. Some of these may cause diagnostic difficulty and potentially be mistaken for neoplasms. Some neoplasms may resemble hamaratomas. Here we review the current clinical and pathologic features of these lesions, both common and rare, and discuss how to distinguish them from other entities in the differential diagnosis.

Congenital fibroblastic connective tissue nevi: Unusual and misleading presentations in three infantile cases

BACKGROUND

Fibroblastic connective tissue nevi (FCTN) are benign skin conditions characterized by bland spindle cells infiltrating the reticular dermis and the upper subcutis with preservation of adnexal structures. A subset of FCTN expresses CD34, which may cause difficulties in the differential diagnosis, in particular with dermatofibrosarcoma (DFSP). We aim to study clinical and histological main features of congenital FCTN to better understand their heterogeneity.

METHODS

We present 3 cases of congenital FCTN with misleading pseudo-tumoral presentations and compare them with published cases in literature. We provide a diagnostic algorithm for congenital neonatal connective tissue tumors.

RESULTS

Clinically, FCTN mostly present as well-limited and nontender plaques or nodules mainly located in the neck and face areas or in the trunk. Histologically, FCTN are composed of irregularly distributed fascicles of bland spindled cells and are defined by a list of fundamental features: (i) no atypia, pleomorphism, or mitotic activity; (ii) skin appendages entrapped but unaffected; (iii) no evidence for malignancy. In most cases CD34 is positive, but in some cases, cells can express SMA or are even CD34- and SMA-.

CONCLUSION

The initial presentation and natural history of FCTN fit better with a neoplasm than with a hamartoma. Thus, we suggest replacing the term "nevus" with tumor and considering fibroblastic connective tissue tumor (FCTT) as the right denomination of this clinico-pathological entity. FCTTs are difficult to diagnose due to their clinical heterogeneity. Clinical and histological malignant and benign differential diagnoses are discussed.