NODULAR MELANOCYTIC NEVI IN THE FIBROUS CAPSULE OF AXILLARY LYMPH NODE. REPORT OF A CASE. F. Tallarigo, I. Putrino, A.V. Filardo°, S. Squillaci°° Anatomia Patologica Ospedale San Giovanni di Dio (Crotone), ° Anatomia Patologica Azienda Ospedaliera Pugliese-Ciaccio (Catanzaro); °° Anatomia Patologica, Ospedale di Vallecamonica, Esine (BS)

INTRODUCTION: Descriptions of intranodal melanocityc nevocellular inclusion (nodal nevi) have been reported periodically over the year. Nodal nevi predominantly form compact focal aggregates in the fibrous capsule of limph-nodes, although they recently have been described in the nodal parenchyma and sinusoids. The incidence in regional lymph-nodes, exicysed for malignancyas been reported, 1% and 22%. The mechanism by which benign melanocytes are transported to lymph nodes is the subject of controversy. Prevailing theories include lymphatic node in the lymphatic drainage basin and an embryologic phenomenon whereby neural crest-derived melanocytes are transported to lymph nodes during in utero migration.

MATERIALS AND METHODS: A 46-year-old woman is referred to our hospital for surgical treatment of a right breast tumor. A quadrantectomy with homolateral axillary lymph node clearance is performed. Histopathology reveals a moderately- differentiated ductal adenocarcinoma (G2) sec. Elston and Ellis in the right breast with tumour invasion in four of the 31 dissected axillary lymph nodes. One of the tumor free lymph nodes shows an intracapsular cluster of normal-appearing, sparsely pigmented, nevus cells with an inconspicuous nucleolus and without nuclear pleomorphism and involvement of the nodal parenchyma.

The cells are diffusely and brightly positive for S-100 protein. The pattern of HMB45 and Mart-1 expression was focal and weaker than was S-100 protein expression. Mitotic figures are rare (Ki67<1%).Therefore, the histological features and immunohitochemical findings in combination help establish the diagnosis of an axillari lymph nodal intracapsular melanocytic nevus. Patient’s history was negative malignant melanoma and congenital malanocytic nevi.

DISCUSSION AND CONCLUSIONS : Since the initial description of benign nodal nevi by Stewart and Copeland in 1931, controversy has existed regarding the means whereby benign nevocellular aggregates come to reside in limph nodes, and this issue is largely unresolved. Both embryologic and mechanical transport hypotheses have been postulated. The majority of investigators believe these inclusions to be benign, and similarities between nodal nevus cells and cutaneous nevocytes have been documented by electron microscopic and immunohistochemical studies. A recent suty demonstrated some immunohistochemical differences in an attempt to aid in their distinction.

Substantial evidence favors the mechanical transport hypothesis. Studies have demonstrated an increased incidence of nodal nevi in the lymph nodes excised from the drainage basin of a primary melanoma, compared with lymph nodes excised for other malignant neoplasms. The high incidence of presumably nodal nevi in sentinel lymph node (SLNs) strongly, of a primary melanoma, supports the hypothesis of mechanical transport through lymphaties. The relative paucity of descriptions of nodal nevi in deep intra-abdominal and intrathoracic limp nodes, which presumably do not collect material from cutaneous drainage basins, also tends to support the mechanical transport theory.

Some have argued that the statistically significant association of nodal nevi with congenital nevi supports an embryologic origin. Previous studies describing the incidence of nodal nevi in lymph node dissections performed for other malignant neoplasms. Such as breast or prostate carcinoma, have demonstrated a very low incidence of nodal nevi. While definitive resolution of the question of nodal nevus origin awaits further study, we confirm the correlation between the incidence of nodal nevi and the presence of melanoma with an associated precursor melanocytic lesion.

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