Definition of Hygroma
A hygroma is a fluid-filled collection that can occur in different anatomical locations, with two main types being subdural hygromas (fluid collections between the dura and arachnoid membranes) and cystic hygromas (lymphatic malformations typically found in the neck region). 1
Types of Hygromas
Subdural Hygromas
- Subdural hygromas are collections of cerebrospinal fluid (CSF) that accumulate in the subdural space, often following trauma or due to spontaneous intracranial hypotension 2
- They commonly develop when there is separation at the dura-arachnoid interface, allowing CSF to accumulate in this potential space 2
- Most subdural hygromas are considered an epiphenomenon of head injury and resolve spontaneously as the brain expands 2
- Some subdural hygromas may evolve into chronic subdural hematomas if conditions persist over several weeks 2
Cystic Hygromas (Lymphatic Malformations)
- Traditionally referred to as "cystic hygromas" or "lymphangiomas," these are actually lymphatic malformations that result from abnormal development of the lymphatic system 3, 1
- They are subdivided into microcystic and macrocystic varieties based on the predominant lacuna size 3
- These malformations are commonly found in the neck region and can be detected prenatally or postnatally 4
- A characteristic feature is the presence of a midline septum on imaging studies 4
Etiology
Subdural Hygromas
- Traumatic brain injury is a common cause, with even trivial trauma potentially leading to dura-arachnoid separation 2
- Spontaneous intracranial hypotension due to CSF leakage through dural defects 1
- Brain atrophy, excessive dehydration, or decreased intracranial pressure can contribute to hygroma formation 2
- Downward traction on meninges due to decreased CSF volume can lead to hygroma formation 1
Cystic Hygromas (Lymphatic Malformations)
- Lymphatic dysplasia characterized by lack of communication between lymphatic system and venous drainage 1
- Chromosomal abnormalities, particularly Turner syndrome (45,X), are associated with 50-80% of cystic hygromas 1
- Developmental failure of lymphatic vessels to connect properly with the venous system 1
Clinical Presentation
Subdural Hygromas
- Many are clinically "silent" with minimal or no symptoms 5
- When symptomatic, patients may present with headache that can be orthostatic (worsens when upright, improves when lying down) 1
- Consciousness disturbance may occur in some cases 6
- Clinical presentation is often more related to associated brain injuries rather than the hygroma itself 5
Cystic Hygromas (Lymphatic Malformations)
- Visible or palpable mass, typically in the neck region 1
- Bleeding into vesicles at the surface of skin or mucosa may occur 3
- In severe prenatal cases, hydrops fetalis may develop 1
- May be associated with other congenital anomalies, particularly when related to chromosomal disorders 1
Diagnosis
Subdural Hygromas
- CT scan shows hypodense fluid collections in the subdural space 5
- MRI with contrast may show pachymeningeal enhancement and engorgement of venous sinuses 3, 1
- Associated findings may include dilated epidural venous plexus and other signs of CSF leakage 1
Cystic Hygromas (Lymphatic Malformations)
- Prenatal ultrasound is the primary diagnostic modality, often showing multiloculated cystic masses with septations 4
- Postnatal diagnosis may involve ultrasound, CT, or MRI depending on the clinical scenario 1
- Karyotype analysis is recommended when detected prenatally due to association with chromosomal abnormalities 1
Management
Subdural Hygromas
- Most subdural hygromas resolve spontaneously and can be managed conservatively with observation 2, 5
- Surgical intervention (burr hole drainage) is only indicated when there is significant mass effect or neurological deterioration 5, 6
- Treatment decisions should be based on clinical presentation rather than imaging appearance alone 5
Cystic Hygromas (Lymphatic Malformations)
- Management depends on size, location, and associated complications 1
- Surgical excision may be considered for large or symptomatic lesions 1
- Novel approaches such as sclerotherapy or targeted medical therapies may be options in certain cases 7
Clinical Pearls and Pitfalls
- Terminology confusion is common, with cystic hygromas historically being called "lymphangiomas," which incorrectly implies proliferative potential 3, 1
- Subdural hygromas can sometimes be mistaken for subdural hematomas on imaging, requiring careful radiological assessment 6
- Outcome of patients with subdural hygromas is more closely related to the primary head injury than to the hygroma itself 2, 5
- The presence of cystic hygromas prenatally warrants thorough evaluation for associated chromosomal abnormalities 1